Endophytes are microbes which reside inside the plant tissues asymptomatically or causing pathogenicity to the host plant for a brief period. Owing to their presence in a specialized niche, endophytes are capable of synthesizing diverse types of bioactive molecules. Continuous development of resistance mechanism by pathogens to the currently available health treatments and pharmaceuticals has led researchers to explore new therapeutic agents. Quorum sensing has a role in the development of microbial pathogenic traits including biofilm formation. Utilization of quorum sensing (QS) inhibitors in antivirulence approach against pathogenesis is one of the innovative strategies. Endophytic microbes provide a plethora of such required bioactive molecules. This review summarizes the bioprospecting of endophytic microbes for production of novel QS inhibitors. At the outset, an overview is presented about the QS and QS inhibition followed by a summary on the endophytes as a treasure trove of bioactive metabolites, particularly the QS inhibitors. Next, we have outlined screening, purification, production, and application of QS inhibitors starting from the isolation of endophytic microbes. There is huge prospect for endophytes in the domain of human healthcare and food industry, provided that we develop a comprehensive understanding of the biology of endophyte and its ecosystem.

Bdellovibrio and like organisms (BALOs) prey on Gram-negative bacteria in the planktonic phase as well as in biofilms, with the ability to reduce prey populations by orders of magnitude. During the last few years, evidence has mounted for a significant ecological role for BALOs, with important implications for our understanding of microbial community dynamics as well as for applications against pathogens, including drug-resistant pathogens, in medicine, agriculture and aquaculture, and in industrial settings for various uses. However, our understanding of biofilm predation by BALOs is still very fragmentary, including gaps in their effect on biofilm structure, on prey resistance, and on evolutionary outcomes of both predators and prey. Furthermore, their impact on biofilms has been shown to reach beyond predation, as they are reported to reduce biofilm structures of non-prey cells (including Grampositive bacteria). Here, we review the available literature on BALOs in biofilms, extending known aspects to potential mechanisms employed by the predators to grow in biofilms. Within that context, we discuss the potential ecological significance and potential future utilization of the predatory and enzymatic possibilities offered by BALOs in medical, agricultural and environmental applications.

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Plant-associated endophytes are recognized as sources of novel bioactive molecules having diverse applications. In this study, an endophytic yeast-like fungal strain was isolated from the fruit of eggplant (Solanum melongena) and identified as Geotrichum candidum through phenotypic and genotypic characterizations. This endophytic G. candidum isolate PF005 was found to emit fruity scented volatiles. The compositional profiling of volatile organic compounds (VOCs) revealed the presence of 3-methyl-1-butanol, ethyl 3-methylbutanoate, 2-phenylethanol, isopentyl acetate, naphthalene, and isobutyl acetate in significant proportion when analyzed on a time-course basis. The VOCs from G. candidum exhibited significant mycelial growth inhibition (54%) of phytopathogen Rhizoctonia solani, besides having mild antifungal activity against a few other fungi. The source of carbon as a nutrient was found to be an important factor for the enhanced biosynthesis of antifungal VOCs. The antifungal activity against phytopathogen R. solani was improved up to 91% by feeding the G. candidum with selective precursors of alcohol and ester volatiles. Furthermore, the antifungal activity of VOCs was enhanced synergistically up to 92% upon the exogenous addition of naphthalene (1.0 mg/plate). This is the first report of G. candidum as an endophyte emitting antifungal VOCs, wherein 2-penylethanol, isopentyl acetate, and naphthalene were identified as important contributors to its antifungal activity. Possible utilization of G. candidum PF005 as a mycofumigant has been discussed based upon its antifungal activity and the qualified presumption of safety status.

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Quorum sensing, the microbial communication system, is gaining importance as a therapeutic target against pathogens. The two key reasons for the rising demand of quorum sensing (QS) inhibitory molecules are low selective pressure to develop resistance by pathogens and possibility of more species-specific effects. Due to complex interactions in a unique niche of live plant tissues, endophytes, as a survival mechanism, potentially produce various bioactive compounds such as QS inhibitors. We report the isolation of an endophytic fungus Kwoniella sp. PY016 from the medicinal plant "Bahera" (Terminalia bellirica), which exhibits substantial quorum sensing inhibition and anti-biofilm activities against the standard test organism, Chromobacterium violaceum. Sugar, sugar alcohol, carboxylic acid, lipid, and phenolic classes of metabolites (predominantly xylitol) are responsible components of the metabolome for the desired bioactivity. A judicious combination of single-factor-at-a-time strategy and artificial neural network modeling combined with genetic algorithm was employed for the selection and optimization of the critical process and medium parameters. Through this newly adopted hybrid model-based optimization, the quorum sensing inhibitory activity of the endophytic metabolome was increased by ~ 30%. This is the first report on optimization of QS inhibitory activity from any fungal endophyte using such a hybrid advanced approach.