CONSTRAINING THE EVOLUTION OF MICROBIAL EXTRACELLULAR ENZYMES IN THE EARLY OCEAN (Invited Presentation)

Microbes that transform and oxidize organic material play a fundamental role in the geochemical cycling of essential elements in seawater. These heterotrophic microbes degrade much of the organic matter produced in the surface ocean, thereby facilitating the recycling of nutrients and carbon throughout the water column. However, most organic matter is physically too large for direct uptake by microbes. Consequently, many heterotrophs secrete hydrolytic enzymes, also known as exoenzymes, to break down large molecules externally into smaller substrates. The evolution of exoenzymes has enabled microbes to access complex marine organic matter, yet their emergence and diversification in early heterotrophs remain poorly understood. In order to constrain when exoenzymes evolved, we quantified the presence of 20 key exoenzymes across eight distinct microbial metabolisms: sulfate reducers, iron (III) reducers, nitrate reducers, methanogens, methanotrophs, oxygenic phototrophs, anoxygenic phototrophs, and aerobic heterotrophs. Preliminary results indicate a prevalence of genes associated with putative exoenzymes across various microbial metabolisms. However, their distribution is correlated with the reduction potential of a metabolism, suggesting that metabolisms with higher redox potential exhibit a greater abundance of these genes. These results imply that the evolution and spread of exoenzymes may have been accelerated by the oxidation of the early ocean.