The Microbial and Metabolic Diversity Associated with Cyanobacteria-Dominated Consortia

Cyanobacteria are considered one of the most successful organisms on the planet. The number of environments in which they persist is matchedonly by their diverse physiological and morphological characteristics. Their evolution, starting approximately 3.8 billion years ago, led to theoxygenation of the earth and the rise of higher eukaryotes. Despite their global importance, much remains unknown regarding how cyanobacteriafunction within these diverse environments and how they shape the world in which we live. Initially this thesis reiterates the uncertainty regardingthe biological origin of nitrogen fixation in complex microbial consortium dominated by a non-heterocystous diazotrophic cyanobacterium. Thisforms the foundation for investigations into the function of enzymes within complex communities using molecular culture-independentapproaches. Using this as inspiration, a novel approach has been developed for investigating the identity and diversity of non-ribosomal peptidesynthetases and polyketide synthases within natural systems. These enzymes are involved in the biosynthesis of many cyanobacterial naturalproducts, including the cyanotoxins. Our proof-of-concept study, first applied to marine sponges, highlights the robust nature of this approach. Thesampling depth obtained far exceeded comparable approaches, and drew attention to the high levels of metabolic diversity that exist within themicrobiomes of these marine animals. The latter chapters of this dissertation study the extent to which cyanobacteria define the complex microbialcommunities in which they dominate. The findings suggest that microbial diversity is dictated by specific strain-strain associations, with changes inthe abundance of key cyanobacteria affecting the entire microbial community. By applying the novel targeted approach to genes involved in naturalproduct biosynthesis in these environments the hypothesis could be tested regarding what influences the prevalence of biosynthetic pathways. It isevident that the diversity of biosynthetic pathways found in an environment is determined, to an extent, by physiological processes occurring withinthat environment. However, the major influencing factor appears to be the presence of key “super-producing” organisms. In conclusion, this thesishas demonstrated new approaches and, in doing so, unveiled both the molecular and metabolic diversity associated with cyanobacteria-dominatedconsortia