title: 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.
authors.affiliation: University of Delaware, Lewes, DE 19958, USA.
authors.forename: Matthew T
authors.initials: MT
authors.lastname: Cottrell
authors.forename: David L
authors.initials: DL
authors.lastname: Kirchman
mesh_terms: D001110:Arctic Regions; D001419:Bacteria / Q000145:classification* / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism*; D001426:Bacterial Proteins / Q000235:genetics; D044822:Biodiversity; D016000:Cluster Analysis; D004269:DNA, Bacterial / Q000737:chemistry / Q000235:genetics; D004275:DNA, Ribosomal / Q000737:chemistry / Q000235:genetics; D005434:Flow Cytometry / Q000379:methods; D008856:Microscopy, Fluorescence / Q000379:methods; D008969:Molecular Sequence Data; D009792:Oceans and Seas; D009930:Organic Chemicals / Q000378:metabolism*; D010788:Photosynthesis; D045322:Photosynthetic Reaction Center Complex Proteins / Q000235:genetics; D010802:Phylogeny; D016133:Polymerase Chain Reaction / Q000379:methods; D012336:RNA, Ribosomal, 16S / Q000235:genetics; D012621:Seasons; D012623:Seawater / Q000382:microbiology*; D017422:Sequence Analysis, DNA
chemical_list: D001426:Bacterial Proteins; D004269:DNA, Bacterial; D004275:DNA, Ribosomal; D009930:Organic Chemicals; D045322:Photosynthetic Reaction Center Complex Proteins; C098543:PufM protein, Bacteria; D012336:RNA, Ribosomal, 16S