Two graduate students- Brent Nowinski and Tito Montenegro- presented exciting Marine Science research at the UGA IOB Symposium (titled Parsing the Microbiome). Below are the abstracts (and additional contributors) associated with the presentations. 

Dimethylsulfoniopropionate Degradation in the Coastal Ocean: Gene- and Taxon-centric Approaches

Brent Nowinski, Christina Preston, Ronald P. Kiene, Christopher Scholin, James Birch, William B. Whitman, Mary Ann Moran

Department of Marine Sciences, Department of Microbiology, University of Georgia; Monterey Bay Aquarium Research Institute; Dauphin Island Sea Lab, University of South Alabama

"Dimethylsulfoniopropionate (DMSP) is an abundant organic sulfur compound produced by marine phytoplankton. Marine bacteria transform DMSP via two pathways: the demethylation pathway retains DMSP-derived sulfur in the cell where it can be incorporated into biomass or be oxidized, while the cleavage pathway releases volatile DMS with potential implications for cloud formation. The prominent hypothesis explaining differential regulation of these pathways poses that demethylation is favored when DMSP dominates the organic sulfur pool, while cleavage is favored when other organic sulfur compounds can substitute as the cellular sulfur source. Marine phytoplankton groups differ in their production and release of DMSP and other organic sulfur compounds, so shifts in phytoplankton community composition can alter sulfur source availability. We tracked bacterial DMSP gene diversity and abundance in Monterey Bay surface waters during a 31-day study in which the Environmental Sample Processor (ESP) autonomously filtered and archived the seawater microbial community. Sequencing of twelve metagenomes during the ESP deployment showed taxa known to carry DMSP genes made up 23-39% of the bacterial community, with SAR11-like cells representing the most abundant DMSP degraders, followed by Roseobacter-, SAR116-, and marine gamma proteobacterium HTCC2080-like cells. Placement of metagenomic reads to reference, assembled, and single-cell genomes revealed seven major clades of DMSP demethylation (dmdA) genes, with SAR11-like cells the source of 56% of placed dmdA reads and having highest abundances in communities with high relative abundances of DMSP producers, including dinoflagellates and haptophytes. Roseobacterlike cells were the source of most of the DMSP cleavage genes, averaging 63% of dddP, dddK, dddQ, and dddD genes, with highest abundances in communities with high relative abundances of small phytoplankton and diatoms. In this coastal system, patterns in DMSP dynamics tracked changes in dominant phytoplankton communities and key bacterial degraders."

Hierarchical classifiers in Transcription Reveal Responses of Extreme Microbial Communities to Oil and Dispersant Exposure.

Tito D. Peña-Montenegro, Sara Kleindienst, Andrew E. Allen, Jonathan Arnold and Samantha B. Joye

Department of Marine Sciences, The University of Georgia, Institute of Bioinformatics, The University of Georgia, J Craig Venter Institute

"Chemical dispersants are used commonly in response to oil spills. However, the impacts of dispersants on microbial community composition and activity are poorly understood. We simulated the deep water conditions that prevailed following the 2010 BP/Deepwater Horizon oil spill and evaluated the response of the microbial community to elevated levels of oil, chemical dispersants and dispersed oil using metatranscriptomics. Clustering factors were compared across levels of a hierarchical annotation system to increase the power of prediction and contrast in our datasets. We found significant dispersant-driven changes in terms of diversity and abundance of microbial composition and activity, shifting the dynamics from one dominated by oil biodegradation in oil-only treatments to those dominated by dispersant biodegradation in dispersant-amended treatments. These results have important implications for understanding the impacts of chemical dispersants on the ability of microbial communities to efficiently degrade oil in the environment."

We are always proud and amazed at our grad students in the Marine Science department, and continue to wish them the best in all their endeavors.