Metabolic characterization of a model heterotrophic bacterium capable of significant chemical alteration of marine dissolved organic matter

The marine bacterium Alteromonas sp. AltSIO was previously found to consume an equivalent magnitude of surface coastal marine dissolved organic carbon (DOC) as diverse bacterial assemblages (Pedler et al., 2014). In this study, we sought to investigate the potential of AltSIO to alter the chemical composition of marine DOC by characterizing its capacity to metabolize a broad suite of environmentally relevant model substrates. Results showed that AltSIO had a particularly broad capacity to degrade carbohydrates relative to other marine bacteria characterized as generalist heterotrophs. Growth in seawater incubations amended with model neutral sugars and radiolabeled substrates showed that AltSIO preferentially utilized d-galactose and disaccharides, but showed little to no biomass incorporation or respiration of d-glucose. Lastly, analysis of ambient dissolved organic matter (DOM) from time-course mesocosms by ultrahigh resolution mass spectrometry showed that both AltSIO grown in pure culture and a mixed bacterial community significantly altered ambient DOM, yet the alteration appeared uniform across chemical classes for both treatments. This study provides insight into the physiological mechanisms of a globally distributed generalist bacterial taxon that has the capacity to significantly alter the geochemistry of marine DOM.