Prasun Kumar

Quorum sensing (QS) is a form of cell-to-cell communication in bacteria which regulates the activities of biofilm formation, virulence, motility, sporulation and antimicrobial resistance. The growing prevalence of multidrug-resistant pathogens complicates the use of traditional antibiotics. Quorum quenching (QQ) enzymes are considered promising anti-virulence molecules that disrupt bacterial communication without any effect on cell viability. The present review is intended to offer a detailed discussion on QQ enzymes in terms of their modes of action, classification, therapeutic applications and existing challenges towards the treatment of bacterial infections. This includes QS circuits of Gram-positive and Gram-negative bacteria such as LuxI/LuxR, Las/Rhl, Agr and AI-2 systems as well as the structure, catalytic actions and substrates of QQ enzymes like AHL lactonases, acylases, oxidoreductases, paraoxonases and peptide-degrading proteases. In addition to this, some recent developments in biomedical and industrial fields involving QQ enzymes for application in biofilm control, antivirulence treatment, agriculture, aquaculture, water decontamination, coating of medical devices and nanobiotechnology are discussed. Novel drug strategies involving phage-based QQ enzymes, nanostructures, genetically modified bacteria, and the synergy between QQ and antibiotics are explained in detail for the treatment of bacteria-related diseases. In conclusion, QQ enzymes represent a promising and sustainable approach to controls bacterial pathogenicity and biofilm-associated infections. Graphical abstract

Polyaromatic hydrocarbons (PAHs) are a group of organic pollutants commonly found in the environment due to industrial activities, incomplete burning of fossil fuels, and oil spills. Bioremediation of PAHs has emerged as a promising approach. This study investigated the biodegradation of PAHs (anthracene, naphthalene, phenanthrene, anthraquinone, and anthrone) at 100 ppm to 1000 ppm in the presence of glucose and glycerol by a biosurfactant-producing strain of Pseudomonas aeruginosa NG4. The quality of the biosurfactant produced by the bacterial strain was analyzed via emulsion index (E24), drop-collapse assay, and oil displacement assay. The PAH degradation efficiency was studied by HPLC and degradation metabolites were analyzed using GC-MS. Among all five PAHs (fed at 300 ppm), the highest degradation rates of 91.16 ± 3.64% naphthalene and 41.16 ± 1.64% anthrone were observed by P. aeruginosa NG4 after 10 days of incubation. The assessment of degradation intermediate metabolites revealed the PAH catabolism via the dioxygenase route, which plays a key role in the breakdown of these aromatic compounds. Biodegradation of anthrone by P. aeruginosa NG4 at a 300 ppm level in the media was reported for the first time. This study highlights the potential of P. aeruginosa NG4 as a candidate for the development of bioremediation strategies to mitigate environmental pollution caused by persistent organic pollutants like PAHs.

Tryptophanase encoded by the gene tnaA is a pyridoxal phosphate-dependent enzyme that catalyses the conversion of tryptophan to indole, which is commonly used as an intra- and interspecies signalling molecule, particularly by microbes. However, the production of indole is rare in eukaryotic organisms. A nucleotide and protein database search revealed tnaA is commonly reported in various Gram-negative bacteria, but that only a few Gram-positive bacteria and archaea possess the gene. The presence of tnaA in eukaryotes, particularly protozoans and marine organisms, demonstrates the importance of this gene in the animal kingdom. Here, we document the distribution of tnaA and its acquisition and expansion among different taxonomic groups, many of which are usually categorized as non-indole producers. This study provides an opportunity to understand the intriguing role played by tnaA, and its distribution among various types of organisms.

BACKGROUND: Oleaginous yeast Naganishia albida is well known for its ability to utilize a variety of carbon sources, including lignocellulosic hydrolysates, complex sugars and fatty acids. In this study, crude glycerol derived from the biodiesel industry and onion waste hydrolysate (OWH) were used as potential substrates for microbial lipid production.RESULTS: Both substrates provided sufficient nutrition to support cell growth and lipid production as sole carbon source. Enhanced lipid production and cell growth rate were observed with supplementation of yeast extract as nitrogen source. Co‐fermentation of OWH and crude glycerol led to improved biomass as well as lipid production. The highest lipid content of 34.0% (w/w) with 21.1 g L⁻¹ of dry cell weight was obtained after 168 h of fed‐batch fermentation with intermittent feeding of crude glycerol and OWH. The lipid concentration was approximately 7 times higher than using mineral medium with crude glycerol as sole carbon source, where a lipid content of 12.6% (w/w) and a maximum biomass of 8.32 g L⁻¹ were obtained at 168 h.CONCLUSION: Optimization of glycerol and OWH feeding could enhance lipid accumulation in N. albida. This study suggests that the co‐fermentation of agricultural and industrial waste as substrates can provide a competitive route for single cell oil production. © 2019 Society of Chemical Industry