Photoheterotrophic Microbes in the Arctic Ocean in Summer and Winter

Abstract

Photoheterotrophic microbes, which are capable of utilizing dissolved organic materials and harvesting light energy, include coccoid cyanobacteria (Synechococcus and Prochlorococcus), aerobic anoxygenic phototrophic (AAP) bacteria, and proteorhodopsin (PR)-containing bacteria. Our knowledge of photoheterotrophic microbes is largely incomplete, especially for high-latitude waters such as the Arctic Ocean, where photoheterotrophs may have special ecological relationships and distinct biogeochemical impacts due to extremes in day length and seasonal ice cover. These microbes were examined by epifluorescence microscopy, flow cytometry, and quantitative PCR (QPCR) assays for PR and a gene diagnostic of AAP bacteria (pufM). The abundance of AAP bacteria and PR-containing bacteria decreased from summer to winter, in parallel with a threefold decrease in the total prokaryotic community. In contrast, the abundance of Synechococcus organisms did not decrease in winter, suggesting that their growth was supported by organic substrates. Results from QPCR assays revealed no substantial shifts in the community structure of AAP bacteria and PR-containing bacteria. However, Arctic PR genes were different from those found at lower latitudes, and surprisingly, they were not similar to those in Antarctic coastal waters. Photoheterotrophic microbes appear to compete successfully with strict heterotrophs during winter darkness below the ice, but AAP bacteria and PR-containing bacteria do not behave as superior competitors during the summer.

Connecting thermal physiology and latitudinal niche partitioning in marine Synechococcus

“…The temperature vs growth curve of the WH8103 strain, isolated in the Sargasso Sea at 28.51N, exhibits a maximum at 28 1C (Moore et al, 1995) and thus supports this conclusion. Our observations support recent surveys which stated that optimum temperature for growth of marine phytoplankton strains is related to the latitude and temperature of their isolation site (Thomas et al, 2012;Boyd et al, 2013), and support field observations that the abundances of the Synechococcus of the 5.1 cluster fall to very low values in the polar oceans, of about hundred cells per ml (Gradinger and Lenz, 1995;Vincent 2000;Not et al, 2004;Cottrell and Kirchman, 2009;Vincent and Quesada, 2012).…”

“…MVIR-18-1 (one of the culture isolates which, to our knowledge, shows the northernmost isolation latitude) can probably survive at temperature below 10 1C, true psychrophilic phytoplankton exhibit optimal temperature lower than 15 1C and can generally not grow over 20 1C (Vincent, 2000;Lovejoy et al, 2007). Although we cannot exclude the existence of true psychrophilic strains within the Synechococcus 5.1 group, as it might be the case for natural Synechococcus subcluster 5.2 populations (Cottrell and Kirchman, 2009;Huang et al, 2011), it appears that northern 5.1 strains might have only moderately decreased their optimal temperature during the evolution and acquired the capacity to stand low temperatures.…”

Novel lineages of Prochlorococcus and Synechococcus in the global oceans

“…This further suggests that Synechococcus that inhabit polar and subpolar waters might be adapted to cold even subzero environments. Picocyanobacterial cell abundance in the Arctic Ocean is typically in the range of 0-10 3 cells per ml (Gradinger and Lenz, 1995;Cottrell and Kirchman, 2009). Coastal waters in the Arctic Ocean can be greatly influenced by river discharges from North America, and allochthonous inputs from riverine picocyanobacteria (in contrast to typical marine picocyanobacteria) to the coastal Arctic waters have been reported (Waleron et al, 2006).…”

“…It appears that picocyanobacterial genotypes present in high-latitude area may vary with specific environments. Picocyanobacteria can survive in the dark season in Arctic or are even more abundant than in spring/summer (Gradinger and Lenz, 1995;Cottrell and Kirchman, 2009). It is of particular interest to explore whether the picocyanobacterial communities are different in dark winter, as their known taxonomic information is mostly confined in summer/autumn.…”

Diversity of Arctic pelagic <i>Bacteria</i> with an emphasis on photoheterotrophs: a review

“…Due to its temperature sensitivity, its concentrations decline rapidly beyond this band (Marchant et al, 1987). Despite its presence was reported in a sub-Arctic region at latitude 61 • N (Buck et al, 1996) and at southern latitudes of the sub-Antarctic (Marchant et al, 1987), Prochlorococcus is considered virtually absent in the polar oceans (Baldwin et al, 2005;Cottrell and Kirchman, 2009;Li, 1994;Lin et al, 2012;Zwirglmaier et al, 2008). Synechococcus is more ubiquitous and inhabits virtually all marine and freshwater environments (Partensky et al, 1999a).…”