At present, anti-virulence drugs are being considered as potential therapeutic alternatives and/or adjuvants to currently failing antibiotics. These drugs do not kill bacteria but inhibit virulence factors essential for establishing infection and pathogenesis through targeting non-essential metabolic pathways reducing the selective pressure to develop resistance. We investigated the effect of naturally isolated plant compounds on the repression of the quorum sensing (QS) system which is linked to virulence/pathogenicity in Pseudomonas aeruginosa . Our results show that trans -cinnamaldehyde (CA) and salicylic acid (SA) significantly inhibit expression of QS regulatory and virulence genes in P. aeruginosa PAO1 at sub-inhibitory levels without any bactericidal effect. CA effectively downregulated both the las and rhl QS systems with lasI and lasR levels inhibited by 13- and 7-fold respectively compared to 3- and 2-fold reductions with SA treatment, during the stationary growth phase. The QS inhibitors (QSI) also reduced the production of extracellular virulence factors with CA reducing protease, elastase and pyocyanin by 65%, 22% and 32%, respectively. The QSIs significantly reduced biofilm formation and concomitantly with repressed rhamnolipid gene expression, only trace amount of extracellular rhamnolipids were detected. The QSIs did not completely inhibit virulence factor expression and production but their administration significantly lowered the virulence phenotypes at both the transcriptional and extracellular levels. This study shows the significant inhibitory effect of natural plant-derived compounds on the repression of QS systems in P. aeruginosa .

Burkholderia thailandensis E264 is a rhamnolipid (RL)-producing gram-negative bacterium first isolated from the soils and stagnant waters of central and north-eastern Thailand. Growth of B. thailandensis E264 under two different incubation temperatures (25 and 30 °C) resulted in a significantly higher dry cell biomass production at 30 °C (7.71 g/l) than at 25 °C (4.75 g/l) after 264 h; however, incubation at the lower temperature resulted in consistently higher concentration of RL production throughout the growth period. After 264 h, the concentration of crude RL extract for the 25 °C culture was 2.79 g/l compared to 1.99 g/l for the 30 °C culture. Overall RL production concentration after 264 h was 0.258 g/g dry cell biomass (DCB) for the 30 °C culture compared to 0.587 g/g DCB for the 25 °C culture. Real-time PCR (qPCR) was also used to analyse expression of the RL biosynthesis genes throughout the incubation period at 25 °C showing that the expression of the rhlA, rhlB and rhlC genes is continuous. During the log and early stationary phases of growth, expression levels remain low and are increased upon entry to the late stationary phase. B. thailandensis E264 produces mostly di-RLs and the Di-RL C14-C14 in most abundance (41.88 %). Fermentations were also carried out in small-scale bioreactors (4 l working volume) under controlled conditions, and results showed that RL production was maintained. Our findings show that B. thailandensis E264 has excellent potential for industrial scale RL production.

Mammals produce volatile odours that convey different types of societal information. In Homo sapiens, this is now recognised as body odour, a key chemical component of which is the sulphurous thioalcohol, 3-methyl-3-sulfanylhexan-1-ol (3M3SH). Volatile 3M3SH is produced in the underarm as a result of specific microbial activity, which act on the odourless dipeptide-containing malodour precursor molecule, S-Cys-Gly-3M3SH, secreted in the axilla (underarm) during colonisation. The mechanism by which these bacteria recognise S-Cys-Gly-3M3SH and produce body odour is still poorly understood. Here we report the structural and biochemical basis of bacterial transport of S-Cys-Gly-3M3SH by Staphylococcus hominis, which is converted to the sulphurous thioalcohol component 3M3SH in the bacterial cytoplasm, before being released into the environment. Knowledge of the molecular basis of precursor transport, essential for body odour formation, provides a novel opportunity to design specific inhibitors of malodour production in humans.

Located at the tip of cell surface glycoconjugates, sialic acids are at the forefront of host–microbe interactions and, being easily liberated by sialidase enzymes, are used as metabolites by numerous bacteria, particularly by pathogens and commensals living on or near diverse mucosal surfaces. These bacteria rely on specific transporters for the acquisition of host-derived sialic acids. Here, we present the first comprehensive genomic and phylogenetic analysis of bacterial sialic acid transporters, leading to the identification of multiple new families and subfamilies. Our phylogenetic analysis suggests that sialic acid-specific transport has evolved independently at least eight times during the evolution of bacteria, from within four of the major families/superfamilies of bacterial transporters, and we propose a robust classification scheme to bring together a myriad of different nomenclatures that exist to date. The new transporters discovered occur in diverse bacteria, including Spirochaetes , Bacteroidetes , Planctomycetes and Verrucomicrobia , many of which are species that have not been previously recognized to have sialometabolic capacities. Two subfamilies of transporters stand out in being fused to the sialic acid mutarotase enzyme, NanM, and these transporter fusions are enriched in bacteria present in gut microbial communities. Our analysis supports the increasing experimental evidence that competition for host-derived sialic acid is a key phenotype for successful colonization of complex mucosal microbiomes, such that a strong evolutionary selection has occurred for the emergence of sialic acid specificity within existing transporter architectures.

Olive mill waste (OMW) creates a major environmental problem due to the difficulty of further waste processing. In this work we present an approach to give OMW added value by using it for the production of biosurfactants. Two bacterial species, Pseudomonas aeruginosa and Bacillus subtilis, were grown with OMW as the sole carbon source. Glycerol and waste frying oil were used as comparative carbon sources. B. subtilis produced surfactin (a lipopeptide) at a maximum concentration of 3.12 mg/L with 2% w/v of OMW in the medium, dropping to 0.57 mg/L with 10% w/v of OMW. In contrast, P. aeruginosa produced 8.78 mg/L of rhamnolipid with 2% w/v OMW increasing to 191.46 mg/L with 10% w/v OMW. The use of solvent-extracted OMW reduced the biosurfactant production by 70.8% and 88.3% for B. subtilis and P. aeruginosa respectively. These results confirm that OMW is a potential substrate for biosurfactant production.