Prokaryotic community structure and heterotrophic production in a river-influenced coastal arctic ecosystem

Abstract

Spatial patterns in prokaryotic biodiversity and production were assessed in the Mackenzie shelf region of the Beaufort Sea during open-water conditions. The sampling transect extended 350 km northwards, from upstream freshwater sites in the Mackenzie River to coastal and offshore sites, towards the edge of the perennial arctic ice pack. The analyses revealed strong gradients in community structure and prokaryotic cell concentrations, both of which correlated with salinity. Picocyanobacterial abundance was low (10 2 to 10 3 cells ml -1 ), particularly at the offshore stations that were least influenced by the river plume. Analysis by catalyzed reporter deposition for fluorescence in situ hybridization (CARD-FISH) showed that the dominant heterotrophic cell types were β-Proteobacteria at river sites, shifting to dominance by α-Proteobacteria offshore. Cells in the Cytophaga-Flavobacter-Bacteroides and γ-Proteobacteria groups each contributed < 5% of total counts in the river, but >10% of counts in the marine samples. Archaea were detected among the surface-water microbiota, contributing on average 1.3% of the total DAPI counts in marine samples, but 6.0% in turbid coastal and riverine waters. 3 H-leucine uptake rates were significantly higher at 2 stations influenced by the river (1.5 pmol l -1 h -1 ) than at other marine stations or in the river itself (≤0.5 pmol -1 h -1 ). Size-fractionation experiments at 2 coastal sites showed that > 65% of heterotrophic production was associated with particles > 3 µm. These results indicate the importance of particleattached prokaryotes, and imply a broad functional diversity of heterotrophic microbes that likely facilitates breakdown of the heterogeneous dissolved and particulate terrestrial materials discharged into arctic seas. KEY WORDS:Prokaryote diversity · Archaea · Proteobacteria · Cytophaga-FlavobacterBacteroides · Arctic Ocean · Mackenzie River estuary · Picocyanobacteria · CARD-FISH Resale or republication not permitted without written consent of the publisherAquat Microb Ecol 42: [27][28][29][30][31][32][33][34][35][36][37][38][39][40] 2006 ments (Payette et al. 2004) may mobilize the large stocks of organic carbon contained within their soils and cause increased transfer of these materials to arctic rivers and ultimately to the ocean. Heterotrophic microbiota are likely to play a major role in the response of coastal arctic ecosystems to ongoing change, but prokaryotic diversity and production in these cold ocean environments have been little explored (Amon 2004).In the western Canadian Arctic, the Mackenzie River discharges large quantities of freshwater, solutes and sediments into a vast shelf region of the Beaufort Sea that extends >100 km offshore and encompasses a total area of 63 600 km 2 (Carmack et al. 2004). The annual discharge of the Mackenzie River (330 km 3 yr -1 ; Macdonald et al. 1998) is the 4th highest in the Arctic Basin after the Siberian rivers Yenisei, Lena and Ob, with concomitantly large inputs of freshwater biota, terrestria...

Dissolved organic matter assimilation by heterotrophic bacterial groups in the western Arctic Ocean

“…Other data suggest that up to 84% of total prokaryotes are active in reducing 5-cyano-2, 3-ditoyl tetrazolium chloride in the western Arctic Ocean (Yager et al 2001, Huston & Deming 2002. These estimates are consistent with studies showing that a high fraction of bacteria (67 to 99%) and archaea (5 to 25%) are detected by fluorescence in situ hybridization (FISH) in Arctic water (Wells & Deming 2003, Garneau et al 2006, Wells et al 2006.…”

“…Other data suggest that up to 84% of total prokaryotes are active in reducing 5-cyano-2, 3-ditoyl tetrazolium chloride in the western Arctic Ocean (Yager et al 2001, Huston & Deming 2002. These estimates are consistent with studies showing that a high fraction of bacteria (67 to 99%) and archaea (5 to 25%) are detected by fluorescence in situ hybridization (FISH) in Arctic water (Wells & Deming 2003, Garneau et al 2006, Wells et al 2006.Several bacterial groups are present in cold environments such as the Arctic Ocean. These groups include Bacteroidetes and several subdivisions of the Proteobacteria (Ferrari & Hollibaugh 1999, Bano & Hollibaugh 2002, Bowman et al 2003.…”

“…Cytophaga-like bacteria are abundant on particles in estuaries and other marine environments (DeLong et al 1993, Crump et al 1999) and appear to favor HMW DOM in the Arctic (the present study) and elsewhere (Cottrell & Kirchman 2000. Concentration of particulate organic carbon decreases from the shelf to the basin (Bates et al 2005), as did the abundance of Cytophaga-like bacteria (the present study), although there was no correlation between Cytophaga-like bacteria and particles in the Beaufort Sea (Garneau et al 2006). The high concentration of particles and the flux of labile DOM may affect the abundance and activity of Cytophaga-like bacteria (Alonso & Pernthaler 2006).…”

Hydrocarbon biodegradation by Arctic sea-ice and sub-ice microbial communities during microcosm experiments, Northwest Passage (Nunavut, Canada)

“…Gammaproteobacteria is typically the predominant group in Arctic sea ice (Junge et al 2002;Brinkmeyer et al 2003;Bowman et al 2012) followed by Bacteroidetes (Deming 2010), whereas Alphaproteobacteria dominates in Arctic surface waters (Garneau et al 2006;Alonso-Sáez et al 2008). Accordingly, our results showed a dominance of Gammaproteobacteria and Bacteroidetes in the marine communities on the underside of landfast ice but no Alphaproteobacteria were detected (Fig.…”

“…This approach measures the production rate of proteins (Kirchman & Ducklow 1993) in both bacteria and archaea (Herndl et al 2005), although we assume a minor contribution of archaea in our samples, as observed on the Beaufort Sea shelf (< 1% to 7% of archaea in total DAPI counts; Garneau et al 2006) and in the Northwest Passage (2 to 13%; Wells & Deming 2003). Triplicate subsamples of 1.2 ml were spiked with 3 H-leucine (specific activity, 60 Ci mmol -1 ) to give a final concentration of 10 nM.…”