Genomic Tools Reveal New Microbial Phototrophs In The Ocean

“It’s an exciting time for microbial oceanography—genomics-based discoveries are changing fundamental paradigms about what kinds of microbes live in marine plankton and how they convert energy from the sun into nourishment for the rest of the oceanic food web,” said Ed DeLong, leader of the research group. The genomic ‘libraries’ of oceanic microbes we study are providing us with a kind of genetic encyclopedia. We can ‘look up’ the identity, properties, and functions of naturally occurring microbes in that encyclopedia. Every time we do, it seems, we find something new.”

In this recent Nature study, MBARI researchers, in collaboration with colleagues from The Institute for Genomic Research, analyzed the genomes of microbes found in Monterey Bay and the central Pacific Ocean. They found that a wide variety of bacterial photosynthetic genes, previously not thought to be significant in marine plankton, are actually widely distributed in ocean waters. The work also showed that the bacterial photosynthetic genes were expressed in oceanic plankton, indicating that these microbes were actively garnering energy from light.

Why is this important? Chlorophyll containing “plant plankton,” or phytoplankton, have long been thought to be the main photosynthetic groups in the ocean. The current MBARI study identifies ecologically significant groups of photosynthetic plankton that don’t contain the chlorophyll found in green plants. The existence of these new types of phototrophs (organisms that get energy directly from light) has stimulated oceanographers to re-think and revise oceanic food web models. Quantifying the impact of such microbes in the food web may help oceanographers balance the global carbon budget sheet.

“Microbial diversity and function in natural environments is not all that well understood. With new tools to compliment more traditional approaches, we can begin to get a more realistic picture of real-world complexity,” said DeLong. “Genomic technology is opening up a whole new and previously unseen world.”