Oxidation state of bioavailable dissolved organic matter influences bacterioplankton respiration and growth efficiency

Abstract Heterotrophic bacterioplankton use oxygen and dissolved organic matter (DOM) to acquire energy, carbon and nutrients necessary for growth; however, the impacts of the chemical composition of DOM on the ratio of oxygen uptake to carbon respiration (i.e., respiratory quotient, RQ) and bacterioplankton growth efficiencies (BGEs) are not well constrained, particularly for nutrient-limited regions such as open oceans. To investigate the influence of DOM composition on RQ we performed DOM remineralization bioassays over a senescing phytoplankton bloom in the eastern North Atlantic Ocean. We found that more oxidized DOM and nitrogen-containing compounds were utilized at lower BGEs and elevated RQs, which we hypothesized to be due to shifts in the energy yield per carbon atom. Results provide important new insights into the molecular mechanisms of the global carbon cycle and have implications for predicting the impacts of future warmer oceans on DOM utilization by bacteria.