Banse Seminar Series, 28 Oct 2020

Wednesday, October 28, 2020

Banse Seminar Series
Patterns of microbe-driven vitamin B12 cycling in Antarctic coastal seas

Deepa Rao
Postdoctoral Researcher, MIT Earth, Atmospheric and Planetary Sciences

2:30 P.M., via Zoom
Meeting ID: 94709092371


Highly productive marine microbial communities in the coastal Southern Ocean sustain the broader Antarctic ecosystem and play a key role in Earth’s climate via the biological pump. Regional phytoplankton growth is primarily limited by light and iron, and can be co-limited by cobalamin (vitamin B12), a trace cobalt-containing organometallic compound only synthesized by some bacteria and archaea. The micronutrient needs of the two keystone phytoplankton types—diatoms and Phaeocystis antarctica—influence local ecology and primary productivity. In this talk, I will describe new insights into patterns of microbe-driven cobalt an B12 cycling in Antarctic coastal waters, focusing on field-based uptake rates and lab-based experiments of microbial ecophysiology. Across Antarctic seas, I measured community-scale cobalt and B12 uptake rates via radiotracer incubation experiments, integrated with hydrographic and phytoplankton pigment data, resulting in the region’s largest dataset of uptake rates to date. Significant correlations were found between uptake fluxes and environmental variables, providing evidence for predominantly diatom-driven uptake in warmer, fresher surface waters with notable regional differences between the Amundsen Sea, Ross Sea, and Terra Nova Bay. In the lab, I grew Phaeocystis antarctica in a matrix of iron and B12 conditions (ranging six orders of magnitude) and investigated its metabolic response to micronutrient stress using complementary proteomics and transcriptomics. We observed colony formation under higher iron treatments, and a facultative use of methionine synthase isoforms depending on B12 availability. I will present multi-omic evidence that P. antarctica is not auxotrophic for the vitamin, and instead modulates its expression of B12-dependent (MetH) and a newly identified putative B12-independent (MetE) methionine synthase, which is also found in other marine microbes with polymorphic life cycles. Together, these findings elucidate possible mechanisms underlying phytoplankton community dynamics in Antarctic seas based on iron and B12 availability that can inform how the microbial community may respond in future climate conditions.

​The Banse Oceanography Seminar Series is named in honor of Dr. Karl Banse, who was recently named as a AAAS fellow, honored for his continuing work on the ecology of the plankton. 

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