The Microbial and Metabolic Diversity Associated with Cyanobacteria-Dominated Consortia

Abstract

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