Marine and aquatic defense strategies

Abstract

Microorganisms have to defend themselves against abiotic threats and have to compete with other organisms. The chemistry of the interactions of microorganisms with their environment has not been studied in detail because most research is focused on the pharmaceutical potential of microbial secondary metabolites.<br /><br />Microorganisms coordinate their lifestyle by chemical signals (quorum sensing) and behave in many aspects like macroorganisms. Thus bacteria form very stable aggregates, so-called biofilms, or produce toxic secondary metabolites. Some bacteria produce spores (dormant and well-protected cells) if living conditions become bad and thus are able to survive for many years.<br /><br />Microorganisms have evolved a large variety of resistance mechanisms against the attack of competitors, for example, drug exporters, restriction enzymes, or DNA repair systems.<br /><br />Microorganisms are well-known producers of complex and toxic metabolites such as polyketides. The high energetic costs of their production indicate their ecological relevance, for example, as weapons to compete with other organisms. An instance is that of the biosurfactant surfactin from Bacillus subtilis, which influences differentiation of Streptomyces coelicolor. Besides small molecules some bacterial enzymes help to compete out other microorganisms: quorum-quenching enzymes break down quorum-sensing signals and consequently confuse foreign bacteria.<br /><br />As symbionts, microorganisms provide their hosts with highly toxic defense compounds, for example, with tetrodotoxin or pederin.