Acylated Homoserine Lactone Signaling in Marine Bacterial Systems

Abstract

This chapter reviews the current understanding of acylated homoserine lactone (AHL) signaling in marine bacterial systems outside of the well-described Vibrio fischeriand Vibrio harveyi models. AHL production has far only been documented in proteobacterial groups. Representatives of these taxa, however, constitute one of the most numerous and functionally diverse classes of microorganisms, and they are particularly abundant in marine environments. Direct chemical analyses, such as those employed by Wagner- Dobler et al., do not have intrinsic biases but are currently at least 10-fold less sensitive than the best biosensors. AHL synthesis is often strongly regulated by other environmental conditions, and these activating conditions may not be recapitulated in standard laboratory culture. The surveys discussed in the chapter should be considered as conservative estimates of AHL production capacity among cultivatable marine bacteria and should be integrated with emerging genomic information on marine bacteria. The Roseobacteria are one of the dominant microbial groups in the ocean, and several subgroups are also the most common AHL signal producers. Ulva zoospores preferentially settled on top of bacteria, suggesting a direct interaction between the bacteria and zoospores and providing evidence that attachment is not a random process. This work led to the discovery that bacterial quorum-sensing molecules, specifically AHLs, are involved in zoospore settlement. The marine environment is a source of abundant materials and resources across the globe. The oceans are sources of diverse and complex quorum-sensing signal molecules produced by many of their endogenous proteobacteria.