Deciphering the tri-dimensional effect of endophytic Streptomyces sp. on chickpea for plant growth promotion, helper effect with Mesorhizobium ciceri and host-plant resistance induction against Botrytis cinerea.

A total of 219 endophytic actinobacteria, isolated from roots, stems and leaves of chickpea, were characterized for antagonistic potential against Botrytis cinerea, causal organism of Botrytis grey mold (BGM) disease, in chickpea. Among them, three most potential endophytes, AUR2, AUR4 and ARR4 were further characterized for their plant growth-promoting (PGP) and nodulating potentials and host-plant resistance against B. cinerea, in chickpea. The sequences of 16 S rDNA gene of the three endophytes were matched with Streptomyces but different species. In planta, the isolate AUR4 alone was able to significantly enhance PGP traits including seed numbers (11.8 vs. 9.8/Plant), seed weight (8 vs. 6.8 g/Plant), pod numbers (13.6 vs. 11.5/Plant), pod weight (9.3 vs. 7.5 g/Plant) and biomass (10.9 vs. 8 g/Plant) over the un-inoculated control in chickpea genotype JG11. Interestingly, consortium of the selected endophytes, AUR2, AUR4 and ARR4 were found less effective than single inoculation. Co-inoculation of the selected endophytes with Mesorhizobium ciceri significantly enhanced nodulation and nitrogenase activity in five chickpea genotypes including ICCV2, ICCV10, ICC4958, Annigeri and JG11 over the un-inoculated control. The selected endophytes showed antagonistic potential in planta by significant reduction of disease incidence (28─52%) in both single inoculation and consortium treatments over the un-inoculated control across the genotypes ICC4954 (susceptible), ICCV05530 (moderately resistant) and JG11 (unknown resistance). Further, antioxidant enzymes such as superoxide dismutase, catalase, ascorbate peroxidase, guaiacol peroxidase, glutathione reductase, phenylalanine ammonia-lyase and polyphenol oxidase and phenolics were found induced in the leaves of chickpea inoculated with selected endophytes over un-inoculated control. Principal component analysis revealed that, the antioxidant enzymes and phenolics were found in the magnitude of ICC4954 < JG11 < ICCV05530 which correlates with their resistance level. The selected endophytes enhanced the plant growth and also host plant resistance against BGM in chickpea.

Plant growth-promoting actinobacteria: a new strategy for enhancing sustainable production and protection of grain legumes.

Grain legumes are a cost-effective alternative for the animal protein in improving the diets of the poor in South-East Asia and Africa. Legumes, through symbiotic nitrogen fixation, meet a major part of their own N demand and partially benefit the following crops of the system by enriching soil. In realization of this sustainability advantage and to promote pulse production, United Nations had declared 2016 as the "International Year of pulses". Grain legumes are frequently subjected to both abiotic and biotic stresses resulting in severe yield losses. Global yields of legumes have been stagnant for the past five decades in spite of adopting various conventional and molecular breeding approaches. Furthermore, the increasing costs and negative effects of pesticides and fertilizers for crop production necessitate the use of biological options of crop production and protection. The use of plant growth-promoting (PGP) bacteria for improving soil and plant health has become one of the attractive strategies for developing sustainable agricultural systems due to their eco-friendliness, low production cost and minimizing consumption of non-renewable resources. This review emphasizes on how the PGP actinobacteria and their metabolites can be used effectively in enhancing the yield and controlling the pests and pathogens of grain legumes.

Plant growth-promoting actinobacteria on chickpea seed mineral density: an upcoming complementary tool for sustainable biofortification strategy.

The present study was evaluated to test the potential of plant growth-promoting actinobacteria in increasing seed mineral density of chickpea under field conditions. Among the 19 isolates of actinobacteria tested, significant (p < 0.05) increase of minerals over the uninoculated control treatments was noticed on all the isolates for Fe (10-38 %), 17 for Zn (13-30 %), 16 for Ca (14-26 %), 9 for Cu (11-54 %) and 10 for Mn (18-35 %) and Mg (14-21 %). The increase might be due to the production of siderophore-producing capacity of the tested actinobacteria, which was confirmed in our previous studies by q-RT PCR on siderophore genes expressing up to 1.4- to 25-fold increased relative transcription levels. The chickpea seeds were subjected to processing to increase the mineral availability during consumption. The processed seeds were found to meet the recommended daily intake of FDA by 24-28 % for Fe, 25-28 % for Zn, 28-35 % for Cu, 12-14 % for Ca, 160-167 % for Mn and 34-37 % for Mg. It is suggested that the microbial inoculum can serve as a complementary sustainable tool for the existing biofortification strategies and substantially reduce the chemical fertilizer inputs.

Plant growth-promoting traits of Pseudomonas geniculata isolated from chickpea nodules.

A bacterium, isolated from nodules of chickpea grown in alluvial soils of Haryana state of India, designated as IC-76 was characterized for in vitro plant growth-promoting (PGP) properties and further evaluated under greenhouse, on-station and on-farm field conditions for PGP activity in chickpea. The isolate IC-76 produced indole acetic acid, siderophore, hydrocyanic acid, cellulase, protease, and ß-1,3-glucanase. When the bacterium was evaluated individually for their PGP potential in the greenhouse on chickpea and in combination with five Streptomyces sp. (strains CAI-24, CAI-121, CAI-127, KAI-32, and KAI-90; demonstrated earlier as biocontrol potential against Fusarium wilt disease in chickpea), the traits, including nodule number and weight, shoot, and root weight, pod number and weight, seed number and weight, available phosphorus and  % organic carbon were found significantly, enhanced over un-inoculated control. In the on-station and on-farm field conditions, IC-76 significantly enhanced nodule number and weight, shoot, and root weight, stover and grain yield and total dry matter. In the rhizosphere (0-15 cm soil), the bacterium also significantly enhanced the total nitrogen, available phosphorus and  % organic carbon. The sequence of 16S rDNA gene of the IC-76 was matched with Pseudomonas geniculata in BLAST analysis. This study demonstrates that IC-76 has the potential for PGP in chickpea.

Plant growth promoting rhizobia: challenges and opportunities.

Modern agriculture faces challenges, such as loss of soil fertility, fluctuating climatic factors and increasing pathogen and pest attacks. Sustainability and environmental safety of agricultural production relies on eco-friendly approaches like biofertilizers, biopesticides and crop residue return. The multiplicity of beneficial effects of microbial inoculants, particularly plant growth promoters (PGP), emphasizes the need for further strengthening the research and their use in modern agriculture. PGP inhabit the rhizosphere for nutrients from plant root exudates. By reaction, they help in (1) increased plant growth through soil nutrient enrichment by nitrogen fixation, phosphate solubilization, siderophore production and phytohormones production (2) increased plant protection by influencing cellulase, protease, lipase and ß-1,3 glucanase productions and enhance plant defense by triggering induced systemic resistance through lipopolysaccharides, flagella, homoserine lactones, acetoin and butanediol against pests and pathogens. In addition, the PGP microbes contain useful variation for tolerating abiotic stresses like extremes of temperature, pH, salinity and drought; heavy metal and pesticide pollution. Seeking such tolerant PGP microbes is expected to offer enhanced plant growth and yield even under a combination of stresses. This review summarizes the PGP related research and its benefits, and highlights the benefits of PGP rhizobia belonging to the family Rhizobiaceae, Phyllobacteriaceae and Bradyrhizobiaceae.

Health benefits of finger millet (Eleusine coracana L.) polyphenols and dietary fiber: a review.

The growing public awareness of nutrition and health care research substantiates the potential of phytochemicals such as polyphenols and dietary fiber on their health beneficial properties. Hence, there is in need to identify newer sources of neutraceuticals and other natural and nutritional materials with the desirable functional characteristics. Finger millet (Eleusine coracana), one of the minor cereals, is known for several health benefits and some of the health benefits are attributed to its polyphenol and dietary fiber contents. It is an important staple food in India for people of low income groups. Nutritionally, its importance is well recognised because of its high content of calcium (0.38%), dietary fiber (18%) and phenolic compounds (0.3-3%). They are also recognized for their health beneficial effects, such as anti-diabetic, anti-tumerogenic, atherosclerogenic effects, antioxidant and antimicrobial properties. This review deals with the nature of polyphenols and dietary fiber of finger millet and their role with respect to the health benefits associated with millet.

Evaluation of Streptomyces strains isolated from herbal vermicompost for their plant growth-promotion traits in rice.

Six actinomycetes, CAI-13, CAI-85, CAI-93, CAI-140, CAI-155 and KAI-180, isolated from six different herbal vermi-composts were characterized for in vitro plant growth-promoting (PGP) properties and further evaluated in the field for PGP activity in rice. Of the six actinomycetes, CAI-13, CAI-85, CAI-93, CAI-140 and CAI-155 produced siderophores; CAI-13, CAI-93, CAI-155 and KAI-180 produced chitinase; CAI-13, CAI-140, CAI-155 and KAI-180 produced lipase; CAI-13, CAI-93, CAI-155 and KAI-180 produced protease; and CAI-13, CAI-85, CAI-140 and CAI-155 produced ß-1-3-glucanase whereas all the six actinomycetes produced cellulase, hydrocyanic acid and indole acetic acid (IAA). The actinomycetes were able to grow in NaCl concentrations of up to 8%, at pH values between 7 and 11, temperatures between 20 and 40 °C and compatible with fungicide bavistin at field application levels. In the rice field, the actinomycetes significantly enhanced tiller numbers, panicle numbers, filled grain numbers and weight, stover yield, grain yield, total dry matter, root length, volume and dry weight over the un-inoculated control. In the rhizosphere, the actinomycetes also significantly enhanced total nitrogen, available phosphorous, % organic carbon, microbial biomass carbon and nitrogen and dehydrogenase activity over the un-inoculated control. Sequences of 16S rDNA gene of the actinomycetes matched with different Streptomyces species in BLAST analysis. Of the six actinomycetes, CAI-85 and CAI-93 were found superior over other actinomycetes in terms of PGP properties, root development and crop productivity. qRT-PCR analysis on selected plant growth promoting genes of actinomycetes revealed the up-regulation of IAA genes only in CAI-85 and CAI-93.

Evaluation of Streptomyces spp. for their plant-growth-promotion traits in rice.

Five strains of Streptomyces (CAI-17, CAI-68, CAI-78, KAI-26, and KAI-27) were previously reported to have potential for charcoal rot control and plant growth promotion (PGP) in sorghum. In this study, those 5 Streptomyces strains were characterized for their enzymatic activities and evaluated for their PGP capabilities on rice. All the Streptomyces strains were able to produce lipase and ß-1,3-glucanase; grew in NaCl (up to 8%), at pH 5-13, and at temperatures 20-40 °C; and were resistant to ampicillin, sensitive to nalidixic acid, and highly sensitive to chloramphenicol, kanamycin, streptomycin, and tetracycline. They were highly tolerant to the fungicide bavistin but were highly sensitive to benlate, benomyl, and radonil. When evaluated on rice in the field, Streptomyces significantly enhanced tiller and panicle numbers, stover and grain yields, dry matter, root length, volume and dry weight, compared with the control. In the rhizosphere at harvest, microbial biomass carbon and nitrogen, dehydrogenase activity, total nitrogen, available phosphorus, and % organic carbon were also found significantly higher in Streptomyces-treated plots than in the control plots. This study further confirms that the selected Streptomyces have PGP activities.

Screening for probiotic properties of strains isolated from feces of various human groups.

The present study searched for potential probiotic strains from various human fecal samples. A total of 67 aerobic and 38 anaerobic strains were isolated from 5 different categories of human feces. Systematic procedures were used to evaluate the probiotic properties of the isolated strains. These showed about 75-97% survivability in acidic and bile salt environments. Adhesion to intestinal cell line Caco-2 was also high. The isolates exhibited hydrophobic properties in hexadecane. The culture supernatants of these strains showed antagonistic effects against pathogens. The isolates were resistant to a simulated gastrointestinal environment in vitro. Of the 4 best isolates, MAbB4 (Staphylococcus succinus) and FIdM3 (Enterococcus fecium), were promising candidates for a potential probiotic. S. succinus was found to be a probiotic strain, which is the second such species reported to date in this particular genus. A substantial zone of inhibition was found against Salmonella spp., which adds further support to the suggestion that the probiotic strain could help prevent intestinal infection. This study suggested that the human flora itself is a potential source of probiotics.

Plant growth-promoting traits of biocontrol potential bacteria isolated from rice rhizosphere.

Seven isolates of bacteria (SRI-156, SRI-158, SRI-178, SRI-211, SRI-229, SRI-305 and SRI-360) were earlier reported by us as having potential for biocontrol of charcoal rot of sorghum and plant growth promotion (PGP) of the plant. In the present study, the seven isolates were characterized for their physiological traits (tolerance to salinity, pH, temperature and resistance to antibiotics and fungicides) and further evaluated in the field for their PGP of rice. All the seven isolates were able to grow at pH values between 5 and 13, in NaCl concentrations of up to 8% (except SRI-156 and SRI-360), temperatures between 20 and 40°C and were resistant to ampicillin (>100 ppm; except SRI-158 and SRI-178) but sensitive (<10 ppm) to chloramphenicol, kanamycin, nalidixic acid, streptomycin (except SRI-156 and SRI-211) and tetracycline. They were tolerant to fungicides benlate and captan, except SRI-158 and SRI-178, bavistin and sensitive to thiram (except SRI-156 and SRI-211) at field application level. In the field, four of the seven isolates (SRI-158, SRI-211, SRI-229 and SRI-360) significantly enhanced the tiller numbers, stover and grain yields, total dry matter, root length, volume and dry weight over the un-inoculated control. In the rhizosphere soil at harvest, all the isolates significantly enhanced microbial biomass carbon (except SRI-156), microbial biomass nitrogen and dehydrogenase activity (up to 33%, 36% and 39%, respectively) and total N, available P and% organic carbon (up to 10%, 38% and 10%, respectively) compared to the control. This investigation further confirms that the SRI isolates have PGP properties.

Assessment of resistomycin, as an anticancer compound isolated and characterized from Streptomyces aurantiacus AAA5.

A new actinomycete strain, isolated from humus soils in the Western Ghats, was found to be an efficient pigment producer. The strain, designated AAA5, was identified as a putative Streptomyces aurantiacus strain based on cultural properties, morphology, carbon source utilization, and analysis of the 16S rRNA gene. The strain produced a reddish-brown pigmented compound during the secondary metabolites phase. A yellow compound was derived from the extracted pigment and was identified as the quinone-related antibiotic resistomycin based on ultraviolet-visible spectrophotometry, fourier transform infrared spectroscopy, liquid chromatography and mass spectroscopy, and nuclear magnetic resonance analyses. The AAA5 strain was found to produce large quantities of resistomycin (52.5 mg/L). It showed potent cytotoxic activity against cell lines viz. HepG2 (hepatic carcinoma) and HeLa (cervical carcinoma) in vitro, with growth inhibition (GI(50)) of 0.006 and 0.005 µg/ml, respectively. The strain also exhibited broad antimicrobial activities against both Gram-positive and Gram-negative bacteria. Therefore, AAA5 may have great potential as an industrial resistomycin-producing strain.