Biology Department Seminar

Many bacteria use cell-cell communication mediated by diffusible signal molecules to monitor particular aspects of their environment such as population density or confinement and, consequently, to modulate their behaviour. In addition to communication between organisms that synthesise the same or related signal molecules, it is becoming evident that bacteria can sense signal molecules that they do not synthesize, thereby eavesdropping on communication by other organisms in their immediate environment. Stenotrophomonas maltophilia is an adaptable organism that is widespread in the environment and is associated with nosocomial colonization and infection as well as with endophytic growth and biocontrol of plant diseases. The genome of S. maltophilia encodes a cell-cell signaling system that is highly related to the diffusible signal factor (DSF)-dependent system of the phytopathogen Xanthomonas campestris. The DSF signal has been characterized as cis-11-methyl-2-dodecenoic acid. In S. maltophilia, DSF signaling controls factors contributing to virulence and antibiotic resistance. In mixed species biofilms, S. maltophilia substantially influences the behavior of P. aeruginosa (which does not synthesize this signal) to develop structures of extended filaments. This effect depends upon the synthesis of DSF by S. maltophilia and could be mimicked by the addition of synthetic DSF. This response of P. aeruginosa to DSF required PA1396, a sensor kinase with an input domain of related amino acid sequence to the sensory input domain of RpfC, which is responsible for DSF perception in xanthomonads. Addition of DSF to P. aeruginosa leads to increased levels of a number of proteins with roles in bacterial stress tolerance, including those implicated in resistance to cationic antimicrobial peptides. Homologues of PA1396 occur in a number of phytopathogenic and plant-associated pseudomonads suggesting that modulation of bacterial behavior through DSF-mediated interspecies signaling