Plankton Genes and Extracellular Organic Substances in the Ocean

Abstract

Dissolved organic matter (DOM) in the ocean represents about 662 billion tons of C, 200 times more than the living biomass. It is produced mainly by microbial primary production. The largest fraction of this DOM is old (>weeks to months) and both chemically and biologically recalcitrant. The remainder is young (seconds to weeks), more labile and surface active. Part of the latter fraction changes the rheological properties in the bulk phase of the water and at interfaces including the sea surface microlayer (SML). In order of abundance, this DOM consists of sugars, amino acids, fatty acids and nucleic acids, often incorporated into complex polymers. The DOM molecules are produced by microbial genes, and are further modified by enzymes themselves produced by genes. The properties of ocean water and its interfaces as well as biogeochemical fluxes may thus be modified by ocean plankton genes. These fluxes influence ocean and atmospheric climate, which in return acts on the biota. Viral infection may furthermore modify prokaryotic and eukaryotic genes and their expression. Therefore, the ocean plankton genomes and the fluxes and climates they influence may be subject to Darwinian-type selection. Research programs need to integrate ocean ecology, rheology, biogeochemistry and genomics, to find the associations among them.