Unboxing PGPR-mediated management of abiotic stress and environmental cleanup: what lies inside?

Abiotic stresses including heavy metal toxicity, drought, salt and temperature extremes disrupt the plant growth and development and lowers crop output. Presence of environmental pollutants further causes plants suffering and restrict their ability to thrive. Overuse of chemical fertilizers to reduce the negative impact of these stresses is deteriorating the environment and induces various secondary stresses to plants. Therefore, an environmentally friendly strategy like utilizing plant growth-promoting rhizobacteria (PGPR) is a promising way to lessen the negative effects of stressors and to boost plant growth in stressful conditions. These are naturally occurring inhabitants of various environments, an essential component of the natural ecosystem and have remarkable abilities to promote plant growth. Furthermore, multifarious role of PGPR has recently been widely exploited to restore natural soil against a range of contaminants and to mitigate abiotic stress. For instance, PGPR may mitigate metal phytotoxicity by boosting metal translocation inside the plant and changing the metal bioavailability in the soil. PGPR have been also reported to mitigate other abiotic stress and to degrade environmental contaminants remarkably. Nevertheless, despite the substantial quantity of information that has been produced in the meantime, there has not been much advancement in either the knowledge of the processes behind the alleged positive benefits or in effective yield improvements by PGPR inoculation. This review focuses on addressing the progress accomplished in understanding various mechanisms behind the protective benefits of PGPR against a variety of abiotic stressors and in environmental cleanups and identifying the cause of the restricted applicability in real-world.

Biosynthesis of silver nanoparticle from flower extract of Dillenia indica and its efficacy as antibacterial and antioxidant.

Dillenia indica is a medicinal tree of the Dilleniaceae and its flower extract was used for the synthesis of silver nanoparticle (AgNPs). The optimal conditions for AgNPs synthesis were as such: 2 mM AgNO3, pH 4.5 and 48-h reaction time. The characteristic band of AgNPs was observed at the wavelength of 435 nm by UV-visible spectroscopic study. Fourier-transform infrared (FTIR) analysis depicted the involvement of several functional groups of plant extracts in the synthesis of AgNPs. Nanoparticles were mostly spherical shaped and uniformly distributed, when observation was made by Transmission electron microscopy (TEM). Energy Dispersive X-Ray (EDX) showed absorption peak approximately at 3 keV thus confirmed the presence of silver metal in AgNP. X-ray diffraction (XRD) investigation and selected area electron diffraction (SAED) patterns showed the crystalline nature of the AgNPs. Dynamic light scattering (DLS) analysis exhibited average size of the nanoparticles as 50.17 nm with a polydispersity index (PDI) value of 0.298. The zeta potential of nanoparticles was observed as -24.9 mV. To assess antibacterial activity, both AgNPs alone or its combination with the antibiotic were tried against six pathogenic bacteria. The combination of AgNPs with antibiotic was maximum effective against Shigella boydii (16.07 ± 0.35) and Klebsiella pneumoniae (15.03 ± 0.20). AgNPs alone showed maximum inhibition for both Gram-positive bacteria: methicillin-resistant Staphylococcus aureus (19.97 ± 0.20 mm) and Enterococcus faecium (19.80 ± 0.15 mm). Maximum inhibition of Enterobactor cloacae and Pseudomonas aeruginosa was observed by antibiotic taken alone. Evaluation through 2,2-diphenyl-1-picrylhydrazyl (DPPH) and DNA nicking assays demonstrated the antioxidant capabilities of the nanoparticles.

Probiotic potential of Streptomyces levis strain HFM-2 isolated from human gut and its antibiofilm properties against pathogenic bacteria.

BACKGROUND: Antimicrobial resistance (AMR) is a serious worldwide public health concern that needs immediate action. Probiotics could be a promising alternative for fighting antibiotic resistance, displaying beneficial effects to the host by combating diseases, improving growth, and stimulating the host immune responses against infection. This study was conducted to evaluate the probiotic, antibacterial, and antibiofilm potential of Streptomyces levis strain HFM-2 isolated from the healthy human gut. RESULTS: In vitro antibacterial activity in the cell-free supernatant of S. levis strain HFM-2 was evaluated against different pathogens viz. K. pneumoniae sub sp. pneumoniae, S. aureus, B. subtilis, VRE, S. typhi, S. epidermidis, MRSA, V. cholerae, M. smegmatis, E. coli, P. aeruginosa and E. aerogenes. Further, the ethyl acetate extract from S. levis strain HFM-2 showed strong biofilm inhibition against S. typhi, K. pneumoniae sub sp. pneumoniae, P. aeruginosa and E. coli. Fluorescence microscopy was used to detect biofilm inhibition properties. MIC and MBC values of EtOAc extract were determined at 500 and 1000 µg/mL, respectively. Further, strain HFM-2 showed high tolerance in gastric juice, pancreatin, bile, and at low pH. It exhibited efficient adhesion properties, displaying auto-aggregation (97.0%), hydrophobicity (95.71%, 88.96%, and 81.15% for ethyl acetate, chloroform and xylene, respectively), and showed 89.75%, 86.53%, 83.06% and 76.13% co-aggregation with S. typhi, MRSA, S. pyogenes and E. coli, respectively after 60 min of incubation. The S. levis strain HFM-2 was susceptible to different antibiotics such as tetracycline, streptomycin, kanamycin, ciprofloxacin, erythromycin, linezolid, meropenem, amikacin, gentamycin, clindamycin, moxifloxacin and vancomycin, but resistant to ampicillin and penicillin G. CONCLUSION: The study shows that S. levis strain HFM-2 has significant probiotic properties such as good viability in bile, gastric juice, pancreatin environment, and at low pH; proficient adhesion properties, and antibiotic susceptibility. Further, the EtOAc extract of Streptomyces levis strain HFM-2 has a potent antibiofilm and antibacterial activity against antibacterial-resistant clinical pathogens.

Induction of systemic resistance in Solanum lycopersicum and Capsicum annum seedlings against Fusarium wilt by Streptomyces bioformulations.

Plant diseases induced by various phytopathogens pose a significant threat to contemporary agricultural systems around the world. In modern agriculture, the use of pesticides is still a valuable and effective method to control plant diseases. However, agrochemicals are becoming less popular because of the accretion of toxic compounds perilous and potentially hazardous to humans and the environment. Taking into consideration these aspects, the present study was conducted to explore the biocontrol potential of an endophytic Streptomyces sp. SP5 bioformulations against Fusarium wilt. Three bioformulations were prepared using cell biomass and different carriers, i.e., B1 (talc-kaolin), B2 (MgSO4/glycerol/Na-alginate/talc/Ca-lignosulfonate), and B3 (calcium carbonate/CMC/talc). Apart from antagonistic action against Fusarium wilt, the influence of bioformulations on plant growth and systemic resistance was investigated by analyzing morphological parameters (root length, shoot length, root weight, shoot weight), biochemical parameters (photosynthetic pigments, non-enzymatic antioxidants), and induction of antioxidative enzymes, e.g., catalase (CAT), ascorbate peroxidase (APX), guaiacol peroxidase (GPX), and superoxide dismutase (SOD), in S. lycopersicum and C. annum seedlings. The results revealed that Streptomyces bioformulations effectively controlled Fusarium wilt in S. lycopersicum and C. annum (82.6-83.4% and 81.8-100%, respectively). Besides reducing disease prevalence, bioformulations significantly increased all the morphological parameters and increased the activity of antioxidative enzymes, i.e., CAT, APX, GPX, and SOD, in plants. The current findings display that bioformulations can be utilized as environment-friendly biocontrol agents against Fusarium wilt and also as plant growth promoters.

Purification and biological analysis of antimicrobial compound produced by an endophytic Streptomyces sp.

Fungal phytopathogens and drug-resistant bacteria are two significant challenges in agriculture and public health, respectively. As a result, new sources of antimicrobial compounds are urgently needed. Taking into consideration these aspects, the present study was carried out to explore the antimicrobial activity of Streptomyces sp. SP5 against drug-resistant bacteria, especially methicillin resistant Staphylococcus aureus (MRSA), vancomycin resistant Enterococcus  and fungal phytopathogens. MRSA and VRE are both types of antibiotic-resistant bacteria that pose significant challenges to public health. In vitro analysis of the metabolites of Streptomyces sp. SP5 exhibited broad-spectrum antimicrobial activity against drug-resistant bacteria and phytopathogenic fungi. Further chemical investigation of the diethyl ether extract led to the isolation and purification of an antimicrobial compound. The structure of the purified compound was elucidated by performing detailed spectroscopic analysis including MS, IR, and NMR. The compound was identified as plicacetin. Plicacetin is a nucleoside antibiotic that has been reported for antibacterial activity against Gram-positive bacterium Mycobacterium tuberculosis. According to our knowledge, the present study is the first to demonstrate the antimicrobial properties of plicacetin against Fusarium oxysporum, Alternaria brassicicola, Fusarium solani, VRE and Bacillus subtilis. The outcome of the current study endorses that compound produced by Streptomyces sp. SP5 can be used as an antimicrobial agent against fungal phytopathogens and drug-resistant bacteria.

Insecticidal potential of endophytic Streptomyces sp. against Zeugodacus cucurbitae (Coquillett) (Diptera: Tephritidae) and biosafety evaluation.

Fruit flies of Tephritidae family pose a serious threat to cultivation of fruits and vegetables across the world. Among them, melon fruit fly, Zeugodacus cucurbitae (Coquillett) (Diptera: Tephritidae) is a devastating pest of plants from Cucurbitaceae family. In a rising concern about the harmful effects associated with the use of chemical insecticides and development of resistance in pest insects, safer pest management strategies such as, use of biopesticides of microbial origin are being contemplated. Therefore, the present study aimed to evaluate the insecticidal potential of Streptomyces sp. SP5 protein extract against Z. cucurbitae. MTT assay, Ames mutagenicity, DNA nicking, and comet assay were conducted to determine the biosafety of protein extract. Second instar larvae of Z. cucurbitae were treated with various concentrations (1, 100, 200, 300, 400, and 500 µg/ml) of Streptomyces sp. SP5 protein extract. The protein extract showed significant larvicidal effects with LC50 value of 308.92 µg/ml. The percentage of adults emerged declined with increase in concentration. There was significant prolongation in developmental durations of the larvae. Various morphological aberrations in the form of deformed adults and pupae and decline in pupal weight were also observed. The nutritional physiology of the treated larvae was also adversely affected. The results from biosafety evaluation revealed antimutagenic and non-toxic nature of Streptomyces sp. proteins. This study indicates that Streptomyces sp. SP5 has the potential to be used as an ecologically safe biocontrol agent against Z. cucurbitae.

Antioxidant and chemoprotective potential of Streptomyces levis strain isolated from human gut.

In the current study, Streptomyces levis strain HFM-2 has been isolated from healthy human gut. Streptomyces sp. HFM-2 was identified based on the polyphasic approach that included cultural, morphological, chemotaxonomical, phylogenetic, physiological, and biochemical characteristics. 16S rRNA gene sequence of strain HFM-2 exhibited 100% similarity with Streptomyces levis strain 15423 (T). The EtOAc extract of Streptomyces levis strain HFM-2 showed potential antioxidant activity, along with 69.53 ± 0.19%, 64.76 ± 0.13%, and 84.82 ± 0.21% of scavenging activity for ABTS, DPPH, and superoxide radicals, respectively at 600 µg/mL. The IC50 values i.e. 50% scavenging activity for DPPH, ABTS, and superoxide radicals were achieved at 497.19, 388.13, and 268.79 (µg/mL), respectively. The extract's reducing power and total antioxidant capacity were determined to be 856.83 ± 0.76 and 860.06 ± 0.01 µg AAE/mg of dry extract, respectively. In addition, the EtOAc extract showed protection against DNA damage from oxidative stress caused by Fenton's reagent, and cytotoxic activity against HeLa cervical cancer, Skin (431) cancer, Ehrlich-Lettre Ascites-E (EAC) carcinoma, and L929 normal cell lines. The IC50 values against HeLa, 431 skin, and EAC carcinoma cell lines were found to be 50.69, 84.07, and 164.91 µg/mL, respectively. The EtOAc extract showed no toxicity  towards L929 normal cells. In addition, flow cytometric analysis exhibited reduced mitochondrial membrane potential (MMP), and enhanced levels of reactive oxygen species (ROS). The EtOAc extract was chemically analyzed using GCMS to determine the components executing its bioactivities.

Biocontrol potential of Streptomyces sp. M4 and salvianolic acid B produced by it against Alternaria black leaf spot.

The proposed study was designed to evaluate the biocontrol potential of Streptomyces sp. M4 and its bioactive metabolites (culture cells/cell free culture supernatant/EtOAc extract/salvianolic acid B) against Alternaria black leaf spot disease. The antifungal metabolite salvianolic acid B attacked A. brassicicola caused fungal abnormalities viz. loss of pigmentation, lysed spores, distorted hyphae and leakage of cellular contents were observed under bright field and scanning electron microscope. The bioactive metabolites in the culture supernatant were found to be thermostable (up to 70 °C), photostable and also stable under acidic and basic conditions. In in vitro experiment, treatment of fungal infected seeds with M4 antagonists (20% of culture supernatant/cells/EtOAc extract/salvianolic acid B) resulted in 82-96% seed germination, 60.71-86.20% healthy seedlings and 1470-2067 seedling vigour as compared to pathogen infected seeds. In vivo pot experiment, in which fungal spores (A. brassicicola) infected Raphanus sativus seeds were treated with Streptomyces sp. M4 culture cells/culture supernatant/EtOAc extract/salvianolic acid B (100 µg/ml), showed increase in various agronomic traits and decrease in disease incidence rate (4-16%) as compared to pathogen treated seeds. In vitro and in vivo studies unveiled that the Streptomyces sp. M4 and its bioactive metabolites could be used as potent biocontrol agents against A. brassicicola infected plants and therefore, to increase the resistance power of plants against pathogens.

Investigating the plant growth promoting and biocontrol potentiality of endophytic Streptomyces SP. SP5 against early blight in Solanum lycopersicum seedlings.

BACKGROUND: Early blight (EB), caused by Alternaria solani, is one of the alarming diseases that restrict tomato production globally. Existing cultural practices and fungicide applications are not enough to control early blight diseases. Therefore, the study aimed to isolate, identify, and characterize an endophytic Streptomyces exhibiting the potential to control early blight in tomato and also promote plant growth. RESULTS: From a Citrus jambhiri leaf, an endophytic Streptomyces sp. with antagonistic activity against Alternaria solani, Colletotrichum acutatum, Cladosporium herbarum, Alternaria brassicicola, Alternaria sp., Fusarium oxysporum and Fusarium sp. was isolated. It was identified as a Streptomyces sp. through 16S ribosomal DNA sequence analysis and designated as SP5. It also produced indole acetic acid which was confirmed by Salkowski reagent assay, TLC and HPLC analysis. Treatment of pathogen infected plants with Streptomyces sp. SP5 antagonists (culture cells/culture supernatant/solvent extract/ acetone precipitates) decreased the early blight disease incidence and significantly increased the various agronomic traits. CONCLUSION: The present study concluded that Streptomyces sp. SP5 possessed antifungal activity against different fungal phytopathogens and had significant potential to control early blight disease and promote plant growth.

Streptomyces hydrogenans strain DH-16 alleviates negative impact of Meloidogyne incognita stress by modifying physio-biochemical attributes in Solanum lycopersicum plants.

The current study assessed the nematicidal and plant growth promoting potential of metabolites produced by Streptomyces hydrogenans strain DH-16 on morphological and physiological activities in 60 days old Solanum lycopersicum plants grown under Meloidogyne incognita stress. M. incognita infestation altered the levels of various photosynthetic pigments, various stress markers, enzymatic and non-enzymatic antioxidants in S. lycopersicum plants grown under in-vivo conditions. However, treatment with culture cells, supernatant and extract produced by S. hydrogenans strain DH-16 significantly reduced the number of galls in M. incognita infested plants when compared with untreated M. incognita infected plants. Moreover, the culture cells/ supernatant/ extract remarkably lowered the levels of stress markers (Hydrogen peroxide and Malondialdehyde) in infected plants and enhanced the activities of non-enzymatic antioxidants (glutathione, tocopherol) and enzymatic antioxidants (Catalase, Superoxide dismutase, Ascorbate peroxidase, Guaiacol peroxidase, Gluatathione-S-transferase and Polyphenol oxidase) in metabolites treated M. incognita infected plants. The enhanced level of different photosynthetic attributes were also evaluated by studying gas exchange parameters and different plant pigments. Moreover, an increment in the content of phenolic compounds such as total phenols, anthocyanin and flavonoids were also reflected in treated and nematode infested plants. The present study also evaluated the microscopic analysis depicting cell viability, nuclear damage and hydrogen peroxide localization in differently treated plants. The outcome of the present study therefore endorses the efficacy of DH-16 as a potential biocontrol agent that help plants in mitigating M. incognita stress.

Insights into the Role of Streptomyces hydrogenans as the Plant Growth Promoter, Photosynthetic Pigment Enhancer and Biocontrol Agent against Meloidogyne incognita in Solanum lycopersicum Seedlings.

Root-knot nematodes (RKN), Meloidogyne sp. hinders functioning of crops and causes global losses in terms of productivity and yield. Meloidogyne sp. are microscopic, obligatory endoparasites with ubiquitous distribution in different parts of the world. Taking into consideration these aspects, the present study was conducted to explore nematicidal activity of the Streptomyces hydrogenans strain DH-16 against M. incognita to regulate its pathogenicity in plants. In-vitro experimentation revealed that pretreated seeds with solvent and culture supernatant lowered root galls in infested plants and promoted growth of Solanum lycopersicum seedlings, revealed through the morphological analysis. Additionally, antioxidative defense responses were induced with microbes. However, oxidative stress markers were considerably reduced after microbial inoculations. Apart from this, secondary metabolites were assessed and modulated in RKN infested plants on microbial supplementations. Confocal studies evaluated glutathione accumulation within root apices and its enhancement was directly proportional to defense responses. Therefore, the current study concluded the role of S. hydrogenans in stimulating antioxidant potential against RKN along with growth promoting aids. Thus, the outcome of the current study endorses that metabolites produced by S. hydrogenans can be used as safe biocontrol agents against M. incognita and also as plant growth promoting agents.

Purification and characterization of salvianolic acid B from Streptomyces sp. M4 possessing antifungal activity against fungal phytopathogens.

The emergence of resistance among fungal phytopathogens poses a biggest threat across the world. Streptomyces are a group of spore-forming Gram + ve bacteria and prolific producers of secondary bioactive metabolites which have been used as biocontrol agents against phytopathogens and also known for plant growth promotion. The current study identified a potent isolate M4 from soil with broad spectrum antifungal activity against different fungal phytopathogens. The isolate was identified as a Streptomyces sp. on the basis of cultural, morphological, physiological, biochemical and phylogenetic characteristics. 16S rRNA gene sequence of M4 showed 100 % similarity with three Streptomyces spp. i.e. Streptomyces plicatus NBRC 13071 T (AB184291), Streptomyces rochei NBRC 12908 T AB184237 and Streptomyces enissocaesilis NRRL-B-16365 T (DQ026641). However, phenotypic and phylogenetic analysis concluded that M4 represents a novel sp. within the genus Streptomyces. One of the two antifungal compounds purified from Streptomyces M4 was identified as salvianolic acid B. To our knowledge, the present study is the first work reporting purification and characterization of salvianolic acid B from Streptomyces and its broad spectrum antifungal activity against different fungal phytopathogens viz. Alternaria spp., Fusarium spp., Colletotrichum spp., Cladosporium herbarum and Botrytis cineria. Salvianolic acid B was found to be photostable, thermostable (up to 70 °C) and non-mutagenic in nature and might be developed as safe biofungicide to control phytopathogens.

Nematicidal potential of Streptomyces antibioticus strain M7 against Meloidogyne incognita.

Meloidogyne spp. are microscopic, obligatory endoparasites with worldwide distribution which cause severe damage to agricultural crops. The present study revealed the nematicidal activity of Streptomyces antibioticus strain M7 against Meloidogyne incognita. The culture supernatant of the isolate caused 100% J2 mortality after 24 h and inhibited egg hatching (only 3%). In addition, the nematicidal activity of actinomycins V, X2 and D purified from strain M7 was also checked. In vitro studies displayed 97.0-99.0% juvenile mortality and 28.0-44.0% egg hatching after 168 h at 240 µg/ml of actinomycin, with LD50 (lethal dose) values of 28-120 µg/ml. In vivo study further validated the nematicidal activity of strain M7, where nematode infested tomato plants treated with culture supernatant/cells/solvent extract showed reduction in root galls and egg masses per plant by 50.0-62.06% and 53.48-76.74%, respectively, and significantly enhanced the shoot length (54.67-76.39%), root length (36.45-64.88%), shoot fresh weight (111-171.77%), root fresh weight (120-163.33%), shoot dry weight (54.45-145.45%), and root dry weight (100-133.3%) over the nematode infested plants treated with water. Furthermore, tomato plants treated with cells/culture supernatant/extract of strain M7 without nematode infestation also showed significant increase in various plant growth parameters. Thus, the outcome of the study revealed the potential of S. antibioticus strain M7 and actinomycins produced from it to be developed as safe nematicidal agents to control the root knot nematodes, and to increase the crop yield.

Biocontrol and plant growth promoting potential of phylogenetically new Streptomyces sp. MR14 of rhizospheric origin.

The detrimental effects of synthetic fungicides have increased the emphasis for biological control as an effective and safe sustainable alternative method. In the present work, a potent rhizospheric actinobacterium MR14 showed broad spectrum antifungal and plant growth promoting activities indicating the potential to fulfill the need. Phylogenetic analysis confirmed that the isolate could be assigned as new species of the Streptomyces, coded as Streptomyces sp. MR14. It formed clade with Streptomyces daghestanicus but with very low bootstrap value (14%). The MR14 supernatant showed potent antagonistic activity against 13 different tested fungal phytopathogens. The most and least sensitive fungal phytopathogens were found to be Pyricularia oryzae and Fusarium oxysporum with inhibition zones of 31 mm and 11 mm, respectively. The antifungal metabolites produced by strain MR14 were thermostable, photostable, and remained active at extreme acidic and neutral pH. In pot experiments, the Streptomyces sp. MR14 cells, supernatant and extract significantly suppressed Fusarium wilt caused by Fusarium moniliforme in tomato plants. Various growth parameters such as shoot and root lengths, and plant fresh and dry weights were significantly enhanced by 19.65 to 321.62% over the pathogen infested plants only. The treatment with culture cells/supernatant/extract in the rhizosphere soil also reduced the microbial count as compared to control. In addition, the strain also possessed plant growth promoting potential which was indicated by the increase in various agronomic traits from 3.64 to 116.88%. This study provided a scientific validation that the new rhizobacterium Streptomyces sp. MR14 could be further developed as bioformulation, exhibiting biocontrol and plant growth promoting capabilities.

Purification and characterization of actinomycins from Streptomyces strain M7 active against methicillin resistant Staphylococcus aureus and vancomycin resistant Enterococcus.

BACKGROUND: The increased rate of resistance among two highly concerned pathogens i.e. methicillin-resistant Staphylococcus aureus (MRSA) and vancomycin-resistant Enterococcus (VRE) necessitates the discovery of novel anti-MRSA and anti-VRE compounds. In microbial drug discovery, Streptomyces are well known source of two-thirds of natural antibiotics used clinically. Hence, screening of new strains of streptomycetes is the key step to get novel bioactive compounds with antimicrobial activity against drug resistant bacteria. RESULTS: In the present study, Streptomyces antibioticus strain M7, possessing potent antibacterial activity against different pathogenic bacteria, was isolated from rhizospheric soil of Stevia rebudiana. 16S rRNA sequence of M7 (1418 bp) showed 96.47-100% similarity with different Streptomyces spp. and the maximum similarity (100%) was observed with Streptomyces antibioticus NBRC 12838T (AB184184). Phylogenetic analysis using neighbor joining method further validated its similarity with Streptomyces antibioticus NBRC 12838 T (AB184184) as it formed clade with the latter and showed high boot strap value (99%). Antibacterial metabolites isolated from the fermentation broth were characterized using NMR, FT-IR and LC-MS as actinomycins V, X2 and D. The purified actinomycins exhibited potent antibacterial activities against test bacteria viz. B. subtilis, K. pneumoniae sub sp. pneumoniae, S. aureus, S. epidermidis, S. typhi, E. coli, MRSA and VRE. Among these actinomycins, actinomycin X2 was more effective as compared to actinomycins D and V. The minimum inhibitory concentration values of purified compounds against a set of test bacterial organisms viz. VRE, MRSA, E. coli (S1-LF), K. pneumoniae sub sp. pneumoniae and B. subtilis ranged between 1.95 and 31.25 µg/ml. CONCLUSIONS: This study demonstrates that actinomycins V, X2 and D produced by S. antibioticus strain M7 hold the potential to be used against multidrug resistant bacteria, particularly VRE and MRSA.

Phenolic compounds as antioxidants and chemopreventive drugs from Streptomyces cellulosae strain TES17 isolated from rhizosphere of Camellia sinensis.

BACKGROUND: Oxidative stress in an intracellular environment created by the accumulation of reactive oxygen species results in oxidative damage to biomolecules which ultimately become a hallmark for severe diseases like cancer, aging, diabetes, and cardiovascular and neurodegenerative diseases. METHODS: Various in vitro assays were employed to assess the antioxidant potential of strain, DNA protective activity was demonstrated using DNA nicking assay and cytotoxicity of the extract was evaluated using MTT assay. Further identification of the compounds was done using UPLC analysis. RESULTS: The extract of Streptomyces cellulosae strain TES17 demonstrated significant antioxidant activity with percentage inhibition of 78.47 ± 0.23, 91.08 ± 0.98 and 82.08 ± 0.93 for DPPH, ABTS and superoxide radical assays at 5 mg/mL, respectively. Total antioxidant and reducing power were found to be 76.93 ± 0.76 and 231.96 ± 0.51 mg AAE/100 mg of dry extract, respectively. Moreover, the extract was shown to inhibit lipid peroxidation upto 67.18 ± 1.9% at 5 mg/mL. TPC and TFC measured in the extract was 55 mg GAE/100 mg and 11.17 ± 4.05 mg rutin/100 mg, respectively. The protective nature of the TES17 extract to oxidative stress induced damaged DNA was shown by percentage of supercoiled DNA i.e. Form I was increased from 26.38 to 38.20% at concentrations ranging from 2 µg to 10 µg. TES17 extract also showed the cytotoxic activity against lung cancer cell line with 74.7 ± 1.33% inhibition whereas, limited toxicity was observed against normal cell line with percentage viability of 87.71 ± 6.66 at same concentration (30 µg/mL) tested. The antioxidant capacity of extract was well correlated with its TPC and TFC and this in turn was in keeping with the UPLC analysis which also revealed the presence of phenolic compounds that were responsible for the antioxidant and cytotoxic potential of S. cellulosae strain TES17. CONCLUSIONS: The present study describes that S. cellulosae strain TES17 isolated from the rhizosphere of Camellia sinensis (tea) plant; produces potent compounds with antioxidant activity, further might be developed into therapeutic drugs to combat oxidative stress.

Sonochemical synthesis, characterization, antimicrobial activity and textile dyeing behavior of nano-sized cobalt(III) complexes.

Using ultrasonic irradiations, nano-sized cobalt(III) coordination complexes, [Co(NH3)6]Cl3·2H2O (A), [Co(en)3]Cl3·3H2O (B) (en-ethylenediamine) and [Co(dien)2]Cl3·3.5H2O (C) (dien-diethylenetriamine) were synthesized. These complexes were characterized by spectroscopic studies like IR, UV/Visible and NMR. Morphology of these complexes was determined by SEM and particle size with the help of TEM & Zeta-sizer. The comparative thermal stability along with phase difference between nano structures and their respective bulk complexes has been studied by thermal gravimetric analysis (TGA) and X-ray powder diffraction (XRD) study respectively. The dyeing behavior of nano-sized Co(III) complexes and their respective bulks has also been studied (using both exhaust and pad dyeing methods) on cotton and wool fabrics and results shown rationalized dyeing behavior. All these complexes were further tested for antimicrobial activity (against B. subtilis, E. coli, K. pneumoniae, F. oxysporum and A. alternate) and it was observed that nano sized complexes enhanced the activity further.

Evaluation of in vitro and in vivo nematicidal potential of a multifunctional streptomycete, Streptomyces hydrogenans strain DH16 against Meloidogyne incognita.

The present work demonstrated the nematicidal potential of Streptomyces hydrogenans strain DH16 (a strain with strong antagonism against fungal phytopathogens and insect pest) against Meloidogyne incognita. The culture supernatant and solvent extract significantly inhibited egg hatching (almost 100%) along with J2 mortality of more than 95% after 96h. The nematicidal activity of 10-(2,2-dimethyl-cyclohexyl)-6,9-dihydroxy-4,9-dimethyl-dec-2-enoic acid methyl ester (SH2; a new antifungal compound) purified from this streptomycete was also evaluated using different concentrations. The juvenile mortality of the nematode increased with increasing concentration and exposure time and reached the maximum (95%) after 96h at concentration of 100µg/ml. After 160h of incubation, egg hatch of 16% was observed at concentration of 100µg/ml as compared to control where 100% egg hatching was achieved. However, at the highest concentration of the compound (200µg/ml), 100% J2 mortality and 0% egg hatching were observed after 72 and 160h of incubation, respectively. In vivo pot experiments further revealed the nematicidal potential of S. hydrogenans where soil drenching with its culture supernatant and cells effectively controlled root galls, egg masses in nematode infested tomato plants and at the same time promoted the growth of tomato plants. Additionally, in the absence of nematodes, soil drenching with culture supernatant and cells significantly enhanced the various agronomic traits of plants as compared to control plants. Thus, the outcomes of the current study endorse the potential of S. hydrogenans strain DH16 and its metabolites to be developed as safe nematicidal and plant growth promoting agents.

Nanoethosomal formulation for skin targeting of amphotericin B: an in vitro and in vivo assessment.

The present study is envisaged to develop nanoethosomal formulation for enhanced topical delivery of amphotericin B (AmB) for the treatment of cutaneous fungal infections. AmB encapsulated nanoethosomes were prepared using mechanical dispersion method in a strength of 0.1% w/w similar to the strength of marketed topical formulation. Vesicle size of nanoethosomal formulations was found to be in the range of 186 ± 2 to 298 ± 4 nm. The optimized nanoethosomal formulation was further incorporated in gel base to form AmB nanoethogel formulation. Rheological characterization study of nanoethogel demonstrated its viscoelastic nature with high elasticity and resistance to deformation at 37 °C. The yield stress value was found to be 108.05 ± 2.4 and 52.15 ± 0.9 Pa for nanoethogel and marketed gel formulation, respectively. The nanoethogel formulation exhibited 2.7- and 3.5-fold higher steady state transdermal flux and skin deposition of AmB, respectively, in comparison to marketed formulation. Confocal laser scanning microscopy (CLSM) study also revealed enhanced skin permeation and deposition with nanoethogel formulation. In vivo study showed that topical application of nanoethogel does not exhibit any skin irritation as tested by Draize test. The developed formulation, in comparison to the marketed gel, demonstrated a remarkable increase in the antifungal activity against Candida albicans. It is thus corroborated from the above results that nanoethosomal formulation represents an efficacious carrier for effective topical delivery of AmB.

Insecticidal and growth inhibitory potential of Streptomyces hydrogenans DH16 on major pest of India, Spodoptera litura (Fab.) (Lepidoptera: Noctuidae).

BACKGROUND: Destructive impacts of insecticides on non targeted populations necessitate the development of an eco friendly pest control method. Streptomyces spp. are rich source of bioactive secondary metabolites which may provide valuable alternatives to chemical insect-control agents as they can be less toxic and readily biodegradable. Because of its potent biocontrol attributes, ethyl acetate extract of Streptomyces hydrogenans DH16, a soil isolate, was tested to assess its anti-insect potential against polyphagous noctuid, Spodoptera litura. RESULTS: The secondary metabolites in the ethyl acetate extract of S. hydrogenans DH16 exhibited larvicidal and growth inhibitory activities. The results indicated that highest concentration of 1600 µg/ml was significantly effective as 70% larval, 66.66% prepupal and 100% pupal mortality was noticed. The metabolites also prolonged the larval developmental period. The LC50 and LC90 values were 1337.384 and 2070.516 µg/ml, respectively for the insect. Negative effects of S. hydrogenans were also observed on development of the insect. Significant decline in adult emergence, adult longevity, fecundity and % hatching was recorded at higher concentrations along with morphological abnormalities as compared to control. Significant decrease in relative growth and consumption rate, efficiency of ingested and digested food and increase in approximate digestibility in larvae reared on diet supplemented with ethyl acetate extract accounts for the toxic as well as anti-nutritive nature of extract. CONCLUSION: Secondary metabolites in the fermentation broth from S. hydrogenans were toxic to the larvae at higher concentrations whereas lower concentrations significantly reduced the reproductive potential of S. litura. Therefore, these metabolites show considerable potential for incorporation in pest management programmes as new biopesticidal formulation.