Marine extracellular ecosystem biology

Microbes are the engines driving the global cycling of nutrients since they have the genes encoding for the main proteins/enzymes involved in the transformation of energy and matter in the ocean. Thus, microbial activities/functions are fundamental to how the ocean operates with implications ranging from fisheries to climate change. During the last 10 years, millions of genes have been retrieved from the ocean. Yet, we still cannot assign function to ca. 50% of these genes. Interestingly, most of these genes are normally interpreted from an intra-cellular functioning perspective. Recent evidence suggest that there are many proteins secreted out of the cells into the environment (i.e., secretome) mediating processes that can be fundamental for the functioning of the ocean microbiome. A large fraction of such proteins have been found dissolved in seawater where they can remain active at distance from the cells for a prolonged period of time, opening a new dimension of extracellular ecosystem biology in the study of marine microbiology. The main objective of the project is to characterize the marine microbial secretome potential, expression and its taxonomic affiliation, as well study the response of the marine secretome to global environmental change. The following hypotheses will be tested: (1) the potential of marine microbes to secrete proteins is widespread and is fundamental to how the ocean ecosystem operates; (2) specific functions will be key contributors to the secretome expression while others will mostly be cell-associated; (3) global change will affect the activity of key secretome functions/proteins, and thus affect the ecology and biogeochemistry of the ocean via its impact on the secretome. We will combine metagenomic and metatranscriptomics with recently developed approaches in our lab to specifically characterize proteins associated to microbial cells (i.e., proteomics) and also the cell- free ones (i.e., exoproteomics). We will study the marine secretomes seasonal variability in two reference sites (Mediterranean Sea and Atlantic Ocean), and the secretomes spatial heterogeneity using data from global sampling expeditions. With these tools we will fill a critical gap, placing the secretome as a key player into the wider context of marine ecology and biogeochemistry, by opening a whole new dimension (extracellular ecosystem biology) in the study of marine microbiology. Achieving the previous will most likely allow a much deeper understanding of this molecular dimension, having also a deep impact in our comprehension of ocean ecosystem function in a context of global change. The results obtained will impact on a wide range of scientific disciplines ranging from microbiology, microbial ecology, biogeochemistry, systems ecology, natural product chemistry to marine bioprospecting.