Antagonistic potential of rhizobacterial isolates against fungal pathogens causing rhizome rot in turmeric.

The study aims to select potent bacterial antagonists to be used as biocontrol agents against rhizome rot disease in turmeric (Curcuma longa L.). A total of 48 bacterial isolates were isolated from the rhizosphere of turmeric. These isolates were screened for their in vitro antagonism against Fusarium solani FS-01 and Pythium aphanidermatum (ITCC 7908). Production of volatile organic compounds and chitinase activity were also performed. Among the tested isolates, two bacterial isolates (IJ2 and IJ10) showed the highest inhibitory activity against these fungal pathogens. GC/MS analysis of the crude extract produced by Pseudomonas sp. IJ2 and B. subtilis IJ10 was found to contain many bioactive compounds with antifungal and antimicrobial activities. The rhizome treatment with these isolates exhibited the lowest percent disease severity with high biocontrol efficacy against the tested pathogens. These isolates with promising antagonistic potential, therefore, can be used as biocontrol agents against rhizome rot in turmeric.

Chemically characterised Pimenta dioica (L.) Merr. essential oil as a novel plant based antimicrobial against fungal and aflatoxin B1 contamination of stored maize and its possible mode of action.

The chemical characterisation of Pimenta dioica essential oil (PDEO) revealed the presence of 50 components, amongst which α-Terpineol (30.31%) was the major component followed by ß-Linalool (6.75%) and γ-Terpinene (4.64%). The oil completely inhibited the growth of aflatoxin B1 secreting strain Aspergillus flavus LHP-VS-8 and aflatoxin B1 production at 2.5 µL/mL and 1.5 µL/mL, respectively. The oil caused dose dependent reduction of methylglyoxal (an AFB1 inducer), enhanced leakage of Ca2+, Mg2+ and K+ ions and significantly reduced ergosterol content of fungal plasma membrane. During in situ experiments, PDEO exhibited complete protection of fumigated maize cob slices from fungal infestation without affecting seed germination. The chemically characterised PDEO is recommended as a plant based preservative and shelf life enhancer of food commodities by preventing fungal growth, AFB1 production and lipid peroxidation. This is the first report on PDEO as inhibitor of AFB1 secretion and methylglyoxal biosynthesis.

Assessment of chitosan biopolymer encapsulated α-Terpineol against fungal, aflatoxin B1 (AFB1) and free radicals mediated deterioration of stored maize and possible mode of action.

This study reports enhanced efficacy of encapsulated α-Terpineol to control fungal, aflatoxin B1 (AFB1) and free radicals mediated deterioration of stored maize samples. The α-Terpineol loaded chitosan nanoemulsion (α-TCsNe) was characterized through SEM, FTIR and XRD techniques. The α-TCsNe exhibited enhanced antifungal activity against aflatoxin secreting strain of Aspergillus flavus (AF-LHP-S1) and 12 other food borne moulds as well as AFB1 production at 0.4 and 0.3 µL/mL, respectively. Further, α-TCsNe inhibited ergosterol synthesis, methylglyoxal (the aflatoxin enhancer) content and enhanced cellular contents release. α-TCsNe showed enhanced radical scavenging activity with IC50 value equivalent to 39.57 and 6.23 µL/mL for DPPH and ABTS, respectively. In addition, α-TCsNe completely inhibited AFB1 production in stored maize samples during in situ investigation. Overall, α-TCsNe holds a promising potential and can be recommended as a novel antifungal preservative to improve the shelf-life of stored maize samples against fungal and aflatoxin contamination.

Culture-dependent and metagenomic analysis of lesser horseshoe bats' gut microbiome revealing unique bacterial diversity and signatures of potential human pathogens.

Bats are highly diverse and ecologically important mammals. They harbor various bacteria, viruses, and fungal communities that are either beneficial or potentially pathogenic. Extensive metagenomic studies in bats are limited, particularly for the gut, and to date, there are no reports on the bacterial diversity of Rhinolophus monoceros from Meghalaya, India. There are limited studies on the isolation of potential harmful or beneficial bacteria and their interactions with the environment through culture-dependent approaches. Therefore, high-throughput screening was used to understand the population structure, genetic diversity, and ecological role of the microorganisms. High-throughput sequencing of the 16S rRNA marker for gene mapping showed that the gut samples constitute a diverse group of bacteria that is dominated by Proteobacteria, followed by Firmicutes. The bacterial genera Corynebacterium and Mycobacterium were also observed in the Illumina dataset. Illumina sequencing revealed eight bacterial phyla composed of 112 genera. The metagenomic analysis of the OTUs from the gut revealed diverse bacterial communities as well as zoonotic and human pathogens. There were differences in the bacterial communities between the two methods used in this study, which could be related to host specificity, diet, and habitat. The culture-dependent technique resulted in the isolation of 35 bacterial isolates, of which Bacillus cereus and B. anthracis are well-known bacterial pathogens that show virulent traits including hemolytic and proteolytic activities. Pseudomonas stutzeri is an opportunistic human pathogen that was also isolated and showed similar traits. Antibiotic sensitivity tests were performed on all 35 isolates, and different antibiotics were used for Gram-positive and -negative bacteria. The result showed that some isolates are resistant to antibiotics such as penicillin G and Cefoxitin. This report on gut bacterial communities could attract interest in the possibility of isolating and characterizing bacteria for the production of antibiotics, enzymes, plant growth promoters, and probiotics. However, the presence of potential pathogenic bacteria that may impose health hazards cannot be ignored and needs to be studied further.