An important goal of marine biogeochemists is to quantify the rates at which elements cycle through the ocean's diverse microbial assemblage, as well as to determine how these rates vary in time and space. The traditional view that phytoplankton are producers and bacteria are consumers has been found to be overly simplistic, and environmental metagenomics is discovering new and important microbial metabolisms at an accelerating rate. Many nutritional strategies previously attributed to one microorganism or functional group are also or instead carried out by other groups. To tease apart which organism is doing what will require new analytical approaches. Flow cytometry, when combined with other techniques, has great potential for expanding our understanding of microbial interactions because groups can be distinguished optically, sorted, and then collected for subsequent analyses. Herein, we review the advances in our understanding of marine biogeochemistry that have arisen from the use of flow cytometry.
Microbes mediate global biogeochemical cycles through their metabolism, and all metabolic processes begin with the interaction between the microbial cell wall or membrane and the external environment. For all heterotrophs and many autotrophs, critical growth substrates and factors are present within the dilute and heterogeneous mixture of compounds that constitutes dissolved organic matter (DOM). In short, the microbe–molecule interaction is one of the fundamental reactions within the global carbon cycle. Here, I summarize recent findings from studies that examine DOM–microbe interactions from either the DOM perspective (organic geochemistry) or the microbe perspective (microbial ecology). Gaps in our knowledge are highlighted and future integrative research directions are proposed.