Microbial Community Composition and Function in Permanently Cold Seawater and Sediments from an Arctic Fjord of Svalbard

Abstract

Heterotrophic microbial communities in seawater and sediments metabolize much of the organic carbon produced in the ocean. Although carbon cycling and preservation depend critically on the capabilities of these microbial communities, their compositions and capabilities have seldom been examined simultaneously at the same site. To compare the abilities of seawater and sedimentary microbial communities to initiate organic matter degradation, we measured the extracellular enzymatic hydrolysis rates of 10 substrates (polysaccharides and algal extracts) in surface seawater and bottom water as well as in surface and anoxic sediments of an Arctic fjord. Patterns of enzyme activities differed between seawater and sediments, not just quantitatively, in accordance with higher cell numbers in sediments, but also in their more diversified enzyme spectrum. Sedimentary microbial communities hydrolyzed all of the fluorescently labeled polysaccharide and algal extracts, in most cases at higher rates in subsurface than surface sediments. In seawater, in contrast, only 5 of the 7 polysaccharides and 2 of the 3 algal extracts were hydrolyzed, and hydrolysis rates in surface and deepwater were virtually identical. To compare bacterial communities, 16S rRNA gene clone libraries were constructed from the same seawater and sediment samples; they diverged strongly in composition. Thus, the broader enzymatic capabilities of the sedimentary microbial communities may result from the compositional differences between seawater and sedimentary microbial communities, rather than from gene expression differences among compositionally similar communities. The greater number of phylum-and subphylum-level lineages and operational taxonomic units in sediments than in seawater samples may reflect the necessity of a wider range of enzymatic capabilities and strategies to access organic matter that has already been degraded during passage through the water column. When transformations of marine organic matter are considered, differences in community composition and their different abilities to access organic matter should be taken into account.The degradation of marine organic matter in the ocean is due in large part to the concerted effects of microbial communities in the water column and in the sediments, which collectively reprocess and ultimately remineralize most of the organic matter initially produced in the surface ocean (18, 39). These communities rely on extracellular enzymes to hydrolyze high-molecularweight organic matter to sizes sufficiently small for cellular uptake. They then respire a fraction of the organic carbon and excrete transformation products as dissolved organic carbon (DOC) that may in turn be used by other members of the microbial community. The composition and capabilities of heterotrophic microbial communities in seawater and sediments thus play a critical role in the global carbon cycle. Although numerous geochemical investigations of carbon cycling have followed the transformations of particulate organic matter as it s...

Large ancient organic matter contributions to Arctic marine sediments (Svalbard)

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Linking Heterotrophic Microbial Activities with Particle Characteristics in Waters of the Mississippi River Delta in the Aftermath of Hurricane Isaac

“…as in transects covering riverine-to-marine conditions (Ziervogel and Arnosti, 2009) have demonstrated that the capacity for pelagic microbial communities to hydrolyze a suite of complex substrates varies considerably, differences that may be correlated to differences in microbial community composition (Teske et al, 2011;D'Ambrosio et al, 2014). Factors that may drive differences in bacterial community structure and activities at the investigated sites include differences in freshwater influence due to the location of the three sites relative to the river mouth (Liu and Liu, 2015).…”

The phosphorus release pathways and their mechanisms driven by organic carbon and nitrogen in sediments of eutrophic shallow lakes

“…The degradation of organic matter mainly relies on microbial communities and extracellular enzymes (enzymes outside microbial cell membranes) produced by them (Sinsabaugh and Foreman, 2001;Sinsabaugh et al, 2009). Thus far, the studies on extracellular enzymes activities (EEA) have been mainly associated with organic matter degradation by microbes (Teske et al, 2011;Alvarez and Guerrero, 2000;Hiroki et al, 2007) and nutrient limitation (Hill et al, 2012;Hill et al, 2010). Furthermore, EEA was also used to reflect the different trophic status of shallow lakes (Caruso et al, 2005;Kalwasinska and Brzezinska, 2013;Ziervogel et al, 2014) and estimate degradation rates (Jackson et al, 1995;Alvarez and Guerrero, 2000;Sciessere et al, 2011) and turnover times (Misic and Harriague, 2009) of organic matter.…”