title: The nitrogen cycle in cryoconites: naturally occurring nitrification-denitrification granules on a glacier.
abstract: Cryoconites are microbial aggregates commonly found on glacier surfaces where they tend to take spherical, granular forms. While it has been postulated that the microbes in cryoconite granules play an important role in glacier ecosystems, information on their community structure is still limited, and their functions remain unclear. Here, we present evidence for the occurrence of nitrogen cycling in cryoconite granules on a glacier in Central Asia. We detected marker genes for nitrogen fixation, nitrification and denitrification in cryoconite granules by digital polymerase chain reaction (PCR), while digital reverse transcription PCR analysis revealed that only marker genes for nitrification and denitrification were abundantly transcribed. Analysis of isotope ratios also indicated the occurrence of nitrification; nitrate in the meltwater on the glacier surface was of biological origin, while nitrate in the snow was of atmospheric origin. The predominant nitrifiers on this glacier belonged to the order Nitrosomonadales, as suggested by amoA sequences and 16S ribosomal RNA pyrosequencing analysis. Our results suggest that the intense carbon and nitrogen cycles by nitrifiers, denitrifiers and cyanobacteria support abundant and active microbes on the Asian glacier.
authors.affiliation: National Institute of Polar Research, Tokyo, Japan; Transdisciplinary Research Integration Center, Tokyo, Japan.
authors.forename: Takahiro
authors.initials: T
authors.lastname: Segawa
authors.forename: Satoshi
authors.initials: S
authors.lastname: Ishii
authors.forename: Nobuhito
authors.initials: N
authors.lastname: Ohte
authors.forename: Ayumi
authors.initials: A
authors.lastname: Akiyoshi
authors.forename: Akinori
authors.initials: A
authors.lastname: Yamada
authors.forename: Fumito
authors.initials: F
authors.lastname: Maruyama
authors.forename: Zhongqin
authors.initials: Z
authors.lastname: Li
authors.forename: Yuichi
authors.initials: Y
authors.lastname: Hongoh
authors.forename: Nozomu
authors.initials: N
authors.lastname: Takeuchi
mesh_terms: D001419:Bacteria / Q000145:classification / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism*; D000458:Cyanobacteria / Q000145:classification / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism; D058440:Denitrification / Q000235:genetics; D017753:Ecosystem; D005798:Genes, Bacterial; D046448:Ice Cover / Q000737:chemistry / Q000382:microbiology*; D009566:Nitrates / Q000032:analysis; D058465:Nitrification / Q000235:genetics; D058458:Nitrogen Cycle / Q000235:genetics; D009586:Nitrogen Fixation / Q000235:genetics; D012336:RNA, Ribosomal, 16S / Q000235:genetics; D012914:Snow / Q000382:microbiology
chemical_list: D009566:Nitrates; D012336:RNA, Ribosomal, 16S