Bioactive small molecules mediate microalgal-bacterial interactions

Abstract

Microalgae are a diverse group of photosynthetic microorganisms found throughout the eukaryote tree. Although unicellular, they have complex relationships with the bacteria that surround them. These interactions can range from obligate symbiosis, where the bacterium is required for host survival, to pathogenic, where the bacterial pathogen can kill the host alga. The nature of these algal-bacterial interactions appear to be tightly regulated by both algal and bacterial bioactive molecules, creating a complex system of chemical interactions through which these different species can chemically communicate with each other and directly alter the other physiology. In this way the bacterium is able to exploit (and manipulate) its host to become a more conducive habitat (e.g. algal phycosphere, aquatic biofilms, etc.) for bacterial survival. However, the identity of many of these small molecules and the mechanisms by which they control these exchanges are often overlooked or misunderstood. The ability to eavesdrop on the chemical cross talk occurring between algae and bacteria may open up a vast potential for new knowledge, relating to understanding bacterial-algal relationships, evolution and possibly hijacking this communication to better control microbes in commercial systems. This chapter outlines some of the known bioactive chemicals that mediate these microalgal-bacterial interactions, highlighting what is currently known about these systems and areas that need further investigation.