Latitudinal Gradients in Degradation of Marine Dissolved Organic Carbon

Abstract

Heterotrophic microbial communities cycle nearly half of net primary productivity in the ocean, and play a particularly important role in transformations of dissolved organic carbon (DOC). The specific means by which these communities mediate the transformations of organic carbon are largely unknown, since the vast majority of marine bacteria have not been isolated in culture, and most measurements of DOC degradation rates have focused on uptake and metabolism of either bulk DOC or of simple model compounds (e.g. specific amino acids or sugars). Genomic investigations provide information about the potential capabilities of organisms and communities but not the extent to which such potential is expressed. We tested directly the capabilities of heterotrophic microbial communities in surface ocean waters at 32 stations spanning latitudes from 76°S to 79°N to hydrolyze a range of high molecular weight organic substrates and thereby initiate organic matter degradation. These data demonstrate the existence of a latitudinal gradient in the range of complex substrates available to heterotrophic microbial communities, paralleling the global gradient in bacterial species richness. As changing climate increasingly affects the marine environment, changes in the spectrum of substrates accessible by microbial communities may lead to shifts in the location and rate at which marine DOC is respired. Since the inventory of DOC in the ocean is comparable in magnitude to the atmospheric CO2 reservoir, such a change could profoundly affect the global carbon cycle.

Coral and macroalgal exudates vary in neutral sugar composition and differentially enrich reef bacterioplankton lineages

“…Fucoidan is produced by Turbinaria in the cell wall to protect against desiccation (Percival, 1979;Anastasakis et al, 2011) and is a rather large macromolecule (B50 kDa; Chattopadhyay et al 2010). We observed significant removal of fucose from Turbinaria exudate remineralization cultures, consistent with results for the bacterial enzymatic hydrolysis of fucoidan that were conducted at comparable latitudes by Arnosti et al (2011). Porites DOM exudates exhibited neutral sugar distributions that are consistent with those of poritid mucus origins (Coffroth, 1990).…”

Coexisting protist-bacterial community accelerates protein transformation in microcosm experiments

“…The high activity can be attributed to the combination of microorganisms derived from natural seawater and surviving P. aeruginosa, as evidenced by the observation that the enzyme activity associated with surviving and active P. aeruginosa in the Auto-SW+Pa microcosm ( Figure 3G) was lower than in the SW-0.7+Pa microcosm. Arnosti et al (2011), suggested that in seawater the diversity of enzymes that degrade complex substrates is positively correlated with the diversity of the microbial community. Obayashi and Suzuki (2008), also reported that each bacterial isolate shows substrate specificity, whereas a variety of substrates are hydrolyzed by the natural bacterial community in bulk seawater.…”

Extending the analytical window for water-soluble organic matter in sediments by aqueous Soxhlet extraction

“…an important energy supply for microbes in subsurface sediments (Whitman et al, 1998;Parkes et al, 2000;D'Hondt et al, 2004;Biddle et al, 2006;Webster et al, 2006), which play an important role in biogeochemical element cycles (Kvenvolden, 1993;D'Hondt et al, 2002). The preservation mechanisms and availability of organic matter to microbes depends on molecular properties such as composition, size and structure (Weiss et al, 1991;Arnosti et al, 2011). For a better understanding of the biogeochemical processes in the sediment, knowledge of the molecular organic matter composition is a prerequisite, particularly of dissolved organic matter (DOM) which accumulates in interstitial water in the sediment as a result of particulate organic matter depolymerization.…”