Elucidating microbial dynamics on marine aggregates

Sedimentation of organic matter from the surface to the deep ocean is responsible for the sequestration of one third of the atmospheric anthropogenic carbon dioxide. Sedimentation largely occurs via formation and gravitational settling of aggregates, which include decaying phytoplankton, fecal pellets and other forms of particulate matter, distributing energy and chemical compounds throughout the water column. Marine aggregates are hotspots of microbial activity and are colonized by a variety of microorganisms. These play key roles in the recycling of particulate organic matter in the aggregates via their hydrolytic ectoenzymatic activity, releasing dissolved organic matter and nutrients into the surrounding water. Recently, it has been shown that colonization of aggregates mainly occurs in the surface ocean, and that surface-derived microbes are potentially transported by the aggregates into deeper layers of the water column. Furthermore, there is experimental evidence that microbial communities associated with artificial particles are subsequently altered by internal succession through the formation of microniches. However, little is known about the microbial processes on naturally occurring marine aggregates in the water column. In the proposed project, we will investigate the key microbial degradation processes that occur on marine aggregates at different layers of the water column, from the surface to the deep ocean. Following recent discoveries of highly abundant fungi on aggregates in the deep ocean, we will investigate the contribution of fungal activity to total microbial processes in marine aggregates using newly developed methodologies. Furthermore, we will identify microbial colonization patterns of aggregates with distinct origin and composition to determine whether there is a general particle-associated microbiome. The insights of this project will elucidate microbial processes associated with marine aggregates, and will contribute to our understanding of the biogeochemical cycling in the ocean.