Elham Esmaeilishirazifard

Microbial metabolism of quorum-sensing molecules acyl-homoserine lactones, γ-heptalactone and other lactones

The cell-to-cell communication of microorganisms is known to be via exertion of certain chemical compounds (signal molecules) and is referred to as quorum sensing (QS). QS phenomenon is widespread in microbial communities. Several Gram-positive and Gram-negative bacteria and fungi use lactone-containing compounds (e.g. acyl-homoserine lactones (AHLs), γ-heptalactone, butyrolactone-I) as signalling molecules. The ability of microorganisms to metabolise these compounds and the mechanisms they employ for this purpose are not clearly understood. Many studies, however, have focused on identifying AHL and other lactone-degrading enzymes produced by bacteria and fungi. Various strains that are able to utilise these signalling molecules as carbon and energy sources have also been isolated. In addition, several reports have provided evidence on the involvement of lactones and lactone-degrading enzymes in numerous biological functions. These studies, although focused on processes other than metabolism of lactone signalling molecules, still provide insights into further understanding of the mechanisms employed by various microorganisms to metabolise the QS compounds. In this review, we consider conceivable microbial strategies to metabolise AHL and other lactone-containing signalling molecules such as γ-heptalactones.

Genomic and molecular characterization of a novel quorum sensing molecule in Bacillus licheniformis

Quorum sensing molecules (QSMs) are involved in the regulation of complicated processes helping bacterial populations respond to changes in their cell-density. Although the QS gene cluster (comQXPA) has been identified in the genome sequence of some bacilli, the QS system B. licheniformis has not been investigated in detail, and its QSM (ComX pheromone) has not been identified. Given the importance of this antagonistic bacterium as an industrial workhorse, this study was aimed to elucidate B. licheniformis NCIMB-8874 QS. The results obtained from bioinformatics studies on the whole genome sequence of this strain confirmed the presence of essential quorum sensing-related genes. Although polymorphism was verified in three proteins of this cluster, ComQ, precursor-ComX and ComP, the transcription factor ComA was confirmed as the most conserved protein. The cell–cell communication of B. licheniformis NCIMB-8874 was investigated through further elucidation of the ComX pheromone as 13-amino acid peptide. The peptide sequence of the pheromone has been described through biochemical characterisation.

Microbial adaptation to venom is common in snakes and spiders

Animal venoms are considered sterile sources of antimicrobial compounds with strong membrane disrupting activity against multi-drug resistant bacteria. However, bite wound infections are common in developing nations. Investigating the oral and venom microbiome of five snake and two spider species, we evidence viable microorganisms potentially unique to venom for black-necked spitting cobras (Naja nigricollis). Among these are two novel sequence types of Enterococcus faecalis misidentified by commonly used clinical biochemistry procedures as Staphylococcus; the genome sequence data of venom-specific isolates feature an additional 45 genes, at least 11 of which improve membrane integrity. Our findings challenge the dogma of venom sterility and indicate an increased primary infection risk in the clinical management of venomous animal bite wounds. One Sentence Summary Independent bacterial colonization of cobra venom drives acquisition of genes antagonistic to venom antimicrobial peptides.