title: Bacterial community structure on two alpine debris-covered glaciers and biogeography of Polaromonas phylotypes.
abstract: High-elevation cold environments are considered ideal places to test hypotheses about mechanisms of bacterial colonization and succession, and about bacterial biogeography. Debris-covered glaciers (glaciers whose ablation area is mainly covered by a continuous layer of rock debris fallen from the surrounding mountains) have never been investigated in this respect so far. We used the Illumina technology to analyse the V5 and V6 hypervariable regions of the bacterial 16S rRNA gene amplified from 38 samples collected in July and September 2009 at different distances from the terminus on two debris-covered glaciers (Miage and Belvedere--Italian Alps). Heterotrophic taxa-dominated communities and bacterial community structure changed according to ice ablation rate, organic carbon content of the debris and distance from the glacier terminus. Bacterial communities therefore change during downwards debris transport, and organic carbon of these recently exposed substrates is probably provided more by allochthonous deposition of organic matter than by primary production by autotrophic organisms. We also investigated whether phylotypes of the genus Polaromonas, which is ubiquitous in cold environments, do present a biogeographical distribution by analysing the sequences retrieved in this study together with others available in the literature. We found that the genetic distance among phylotypes increased with geographic distance; however, more focused analyses using discrete distance classes revealed that both sequences collected at sites <100 km and at sites 9400-13,500 km to each other were more similar than those collected at other distance classes. Evidences of biogeographic distribution of Polaromonas phylotypes were therefore contrasting.
authors.affiliation: Department of Earth and Environmental Sciences, University of Milano-Bicocca, Milano, Italy.
authors.forename: Andrea
authors.initials: A
authors.lastname: Franzetti
authors.forename: Valeria
authors.initials: V
authors.lastname: Tatangelo
authors.forename: Isabella
authors.initials: I
authors.lastname: Gandolfi
authors.forename: Valentina
authors.initials: V
authors.lastname: Bertolini
authors.forename: Giuseppina
authors.initials: G
authors.lastname: Bestetti
authors.forename: Guglielmina
authors.initials: G
authors.lastname: Diolaiuti
authors.forename: Carlo
authors.initials: C
authors.lastname: D'Agata
authors.forename: Claudia
authors.initials: C
authors.lastname: Mihalcea
authors.forename: Claudio
authors.initials: C
authors.lastname: Smiraglia
authors.forename: Roberto
authors.initials: R
authors.lastname: Ambrosini
mesh_terms: D001419:Bacteria / Q000145:classification / Q000235:genetics; D018407:Bacterial Physiological Phenomena; D015373:Bacterial Typing Techniques; D044822:Biodiversity; D042621:Comamonadaceae / Q000235:genetics / Q000502:physiology*; D046448:Ice Cover / Q000382:microbiology*; D007558:Italy; D058974:Phylogeography; D012336:RNA, Ribosomal, 16S / Q000235:genetics; D012987:Soil / Q000737:chemistry; D012988:Soil Microbiology
chemical_list: D012336:RNA, Ribosomal, 16S; D012987:Soil
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