Quorum signal molecules as biosurfactants affecting swarming in Rhizobium etli

Abstract

Swarming motility is suggested to be a social phenomenon that enables groups of bacteria to coordinately and rapidly move atop solid surfaces. This multicellular behavior, during which the apparently organized bacterial populations are embedded in an extracellular slime layer, has previously been linked with biofilm formation and virulence. Many population density-controlled activities involve the activation of complex signaling pathways using small diffusible molecules, also known as autoinducers. In Gramnegative bacteria, quorum sensing (QS) is achieved primarily by means of N-acylhomoserine lactones (AHLs). Here, we report on a dual function of AHL molecules in controlling swarming behavior of Rhizobium etli, the bacterial symbiotic partner of the common bean plant. The major swarming regulator of R. etli is the cinIR QS system, which is specifically activated in swarming cells by its cognate AHL and other long-chain AHLs. This signaling role of long-chain AHLs is required for high-level expression of the cin and rai QS systems. Besides this signaling function, the long-chain AHLs also have a direct role in surface movement of swarmer cells as these molecules possess significant surface activity and induce liquid flows, known as Marangoni flows, as a result of gradients in surface tension at biologically relevant concentrations. These results point to an as-yet-undisclosed direct role of long-chain AHL molecules as biosurfactants.cell-cell signaling ͉ motility ͉ quorum sensing

Deadly competition between sibling bacterial colonies

“…To coordinate such cooperative ventures, bacteria have developed methods of cell-to-cell signaling (14)(15)(16)(17)(18)(19), including direct physical interactions by extra membrane polymers (20)(21), secretion of extracellular materials like lubricating surfactin (22)(23), biochemical communication such as quorum sensing and chemotaxis signaling (by using mediators ranging from simple molecules and polymers to peptides and complex proteins) (24)(25)(26)(27)(28)(29), and exchange of genetic information (by plasmids and viruses) (30)(31)(32). Bacterial communication-based cooperation can lead to colony morphogenesis, coordinated gene expression, regulated cell differentiation, and division of tasks.…”

Legume seed exudates and Physcomitrella patens extracts influence swarming behavior in Rhizobium leguminosarum

“…Since surfactants and other surface wetting agents may facilitate surface translocation by reducing surface tension, we also investigated the presence of surfactants in the seed exudates using a water droplet spreading assay (Daniels et al 2006), in which a drop of water was placed on top of swarm plates supplemented with the exudates and droplet spreading was observed; surfactants were not detected in the exudates using this method (data not shown). …”

“…Swarming in R. leguminosarum (Tambalo et al 2010c) and the closely related species Rhizobium etli (Daniels et al 2006) have recently been reported and partially characterized. In R. leguminosarum bv.…”

“…viciae remain unknown. In R. etli, swarming is regulated by the CinIRS quorum-sensing system, and the long-chain N-acyl homoserine lactone molecules produced by CinI have biosurfactant-like activity and are present in the extracellular matrix secreted by swarmer cells (Daniels et al 2006). Swarming motility has also been demonstrated in Bradyrhizobium japonicum (Covelli et al 2013) and in Sinorhizobium meliloti (Soto et al 2002;Nogales et al 2010;Gao et al 2012).…”

Pseudomonas aeruginosa fosfomycin resistance mechanisms affect non-inherited fluoroquinolone tolerance

“…PCR amplifications were performed using primers SPI-1559 and SPI-1713 (Table 2). The resulting 460 bp fragments were digested with XbaI and EcoRI, cloned into pUC18, confirmed by sequencing and subcloned into pFAJ1708 (Daniels et al, 2006), resulting in pCMPG13402 (referred to as pFosA) and pCMPG13403 (referred to as pFosA R119A ), constitutively expressing fosA + and fosA R119A , respectively. Plasmids were introduced into P. aeruginosa PAO1 by electroporation (Choi et al, 2006) to obtain strains CMPG13411 and CMPG13435, referred to as PAO(pFosA) and PAO(pFosA R119A ), respectively.…”