The overall goal of this NSF-supported Microbial Observatory is to examine the diversity, abundance and biogeochemical roles of photoheterotrophs in the oceans, with a special focus on Delaware coastal waters (map of study site).
What are photoheterotrophs? Photoheterotrophs are microbes that combine aspects of the metabolisms of both phototrophs and heterotrophs. Click here for the research questions we examine.
Phototrophs obtain their energy from light and their carbon from carbon dioxide (CO2) (photoautotrophy), producing organic material. The other elements necessary for growth (nitrogen and phosphorus, for example) usually come from inorganic sources, such as ammonium (NH4+) and phosphate (PO43-). Examples of common phototrophs include plants on land whereas in the oceans, the main phototrophs are microscopic algae (phytoplankton). Similar to terrestrial plants on land, phytoplankton make up the base of the food chain on which the other marine organisms depend.
Heterotrophs obtain their energy (chemoorganotrophy) and carbon from organic material, producing CO2 in the process. In the oceans, the biggest heterotrophs include fish and whales, but the smallest heterotrophs, bacteria and other microbes, are the ones most important in using organic material produced by phytoplankton (primary production) for energy and carbon. In fact, heterotrophic bacteria and the small protist grazers that eat them consume about 50% of primary production in the oceans. This process is especially important in determining the size and fluxes through the dissolved organic matter (DOM) pool, which includes dissolved organic carbon (DOC). The amount of carbon in the DOC pool is roughly equal to the carbon in atmospheric CO2.
This simple figure illustrates the fate of primary production: 1) large phytoplankton are grazed on by large zooplankton, the pathway that leads eventually to higher trophic levels (e.g. fish) and possible export of carbon via sinking particles; 2) small phytoplankton, including coccoid cyanobacteria, are grazed on by small protist grazers; and 3) the microbial loop, which consist of the production of DOM and its consumption by heterotrophic and phototrophic bacteria. (Click here for a bigger version of the diagram.)