Bacterial signals and antagonists: the interaction between bacteria and higher organisms

It is now well established that bacteria communicate through the secretion and uptake of small diffusable molecules. These chemical cues, or signals, are often used by bacteria to coordinate phenotypic expression and this mechanism of regulation presumably provides them with a competitive advantage in their natural environment. Examples of coordinated behaviors of marine bacteria which are regulated by signals include swarming and exoprotease production, which are important for niche colonisation or nutrient acquisition (e.g. protease breakdown of substrate). While the current focus on bacterial signalling centers on N-Acylated homoserine lactones, the quorum sensing signals of gram-negative bacteria, these are not the only types of signals used by bacteria. Indeed, there appears to be many other types of signals produced by bacteria and it also appears that a bacterium may use multiple classes of signals for phenotypic regulation. Recent work in the area of marine microbial ecology has led to the observation that some marine eukaryotes secrete their own signals which compete with the bacterial signals and thus inhibit the expression of bacterial signalling phenotypes. This type of molecular mimicry has been well characterised for the interaction of marine prokaryotes with the red alga, Delisea pulchra.