Collaborative Research: The Impact of Pelagibacter on DOM Composition Under Light and Dark Conditions

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Heterotrophic bacterial metabolism and photochemical degradation are two of the primary transformative mechanisms for dissolved organic matter (DOM) in the marine environment. In this research, scientists from Woods Hole Oceanographic Institution, Oregon State University and University of Maryland will attack both issues by comparing use of individual compounds of DOM affected by light or by a single bacterial species. Pelagibacter ubique is a ubiquitous marine bacterial species and can represent up to 25% of the heterotrophic bacterial population in the ocean. Although P. ubique has been isolated into laboratory culture and its genome has been sequenced, the growth requirements of this important marine bacterium are not well constrained, although nutrient limitation of P. ubique growth is not alleviated by the addition of inorganic or organic supplements. The scientists will build on their preliminary work that indicates that P. ubique incorporates and produces different compounds when grown under light conditions than under dark conditions, which is surprising since P. ubique exhibits no growth differences under light and dark conditions, despite the presence of a proteorhodopsin proton pump. The researchers will investigate the impact of photochemistry on the suite of compounds incorporated and produced by P. ubique during growth experiments, determining the molecular-level composition of DOM by Fourier Transform Ion Cyclotron Resonance Mass Spectroscopy (FTICR-MS) and its optical characteristics before and after incubation with P. ubique. Identification of growth substrates of P. ubique in the presence and absence of light will be an important step forward in constraining possible substrates for heterotrophic activity in marine systems.An important component of this work will be the continued development of an analytical framework for FTICR-MS data. First, they will further develop work with internal standards and novel spectral alignment algorithms. Second, they will enhance existing automated analytical tools to include ancillary information regarding compound structure and composition such as polarity predictions from liquid chromatography and fragmentation spectra from MS/MS experiments. Their goal is to provide a data analysis pipeline that includes automated calibration, spectral alignment, robust spectral comparisons and elemental formula assignments. Among the broader impacts of this research is the development of an analytical framework for robust and routine examination of FT-ICR MS data that is critical for the applications of this technique to biogeochemistry. The researchers will train graduate students at WHOI, UMD and OSU in FTICR MS and will provide travel funds to graduate students from other institutions in order to disseminate their approach to the broader geosciences community.