| Glaciers contain large part of the earth's microbial biomass and processes with respect to environmental conditions. Bacterial sources and distribution in glacial snow have been proved to be effected by atmospheric circulations and surrounding environments. Reports in which same research methods were used to compare multiple bacterial community structure of glacial snow and further to explore the underlying mechanisms were very limited. Bacterial community structure in snowpack from four glaciers, including Muztaw glacier (MSD) located in Xinjiang Province, Muztagata glacier (MZ) on the Pamir Plateau, Zhadang (ZD) and Yulong (YL) glaciers on the Tibetan Plateau were investigated by constructing bacterial 16S rRNA gene clone libraries. The results showed that:1. The main ions concentrationsConcentrations of the main ions in snowpack varied among the four glaciers. Concentrations of Particles (1< d< 30), Na+ and Cl- changed in the order of ZD> YL> MZ> MSD, their values in ZD were 9,14 and 4 times as high as in MSD, respectively; concentrations of ca2+were higher in YL and MZ than in ZD or MSD.2. Bacterial community diversityA total of 25 bacterial 16S rRNA gene clone libraries were constructed and the bacteria could be classified to 175 OTU. Both of OTUs and diversity indices (Shannon index) varied significantly in one glacier; OTUs varied significantly but diversity indices didn't changed significantly among different glaciers. These results indicated that variation of bacterial diversity among different glaciers was less significant than that in a glacier.3. Bacterial community compositionAnalysis of bacterial 16S rRNA gene clone libraries showed that bacteria community composition changed significantly among different glaciers. (1) NMDS analysis showed a significant changing among the four glaciers. Cluster analysis showed that all the bacterial communities were separated into two groups, one contained samples from the glacier in Xinjiang (MSD) while the other contained samples from the glaciers in (ZD and YL) and beside (MZ) the Tibetan Plateau. These results reflected a significant variation of bacterial community composition at the level of whole community among different glaciers but bacterial community composition in one glacier was more similar. (2) The bacteria were classified into 12 groups, among which Betaproteobacteria (56.66%?63.37%) and Bacteroidetes (21.48%?34.69%) were dominant. Betaproteobacteria increased from MSD to YL while Bacteroidetes decreased. Alphaproteobacteria were more in ZD, MZ, and YL than in MSD. Relative abundance of other groups was low, for example, Cyanobacteria (MSD,0.30%; MZ,2.97%), Firmicutes (MSD, 0.22%; YL,3.48%), Deinococcus-Thermus only occurred in MSD and MZ, Chloroflexi and Acidobacteria were specific for MZ. (3) Bacterial community composition at the level of genus showed that 22 genus were identified in all, they represented 48.17%,44.22%,45.82% and 63.82% of the total clones in MSD, MZ, ZD and YL, respectively. There were 9 identified genus distributed widely in the four glaciers, and the relatively abundant genus belonged to Betaproteobacteria. Polaromonas (24.72%) and Methylibium (10.08%) dominated in MSD; Duganella (11.77%) and Polaromonas (9.85%) were more in MZ; Polaromonas (25.51%) was the only dominant genera in ZD; Duganella and Polaromonas represented high proportions of 23.58% and 22.58% in YL. Flavobacterium, the only identified genera of Bacteroidetes varied obviously among different glaciers (MZ:8.21%; YL:3.99%; MSD:122%; ZD:0.86%). (4) Bacterial community composition at the level of OTU changed significantly among different glaciers. About 1/4 (40/175) of OTUs distributed widely in the four glaciers, more of them were held by Betaproteobacteria (24/80) and Bacteroidetes (8/42).57 representative OTU represented 88.23%, 86.48%,78.94% and 76.60% of the total clones in YL, ZD, MZ and MSD, respectively. Proportions of different representative OTU varied significantly among different glaciers, for example, gls146 (5.22%) and gls252 (3.87%) were specific for MSD, glsll (8.05%) and gls82 (14.08%) were relatively more in MSD while less than 1% in the other three glaciers; gls176 (2.73%) was specific for MZ, proportion of glsl9 in MZ reached 11.56%, while that in the other three were lower than 0.6%; Similarity, relative abundance of gls107, gls54 and gls25 was higher in ZD (3.98%,4.17% and 3.78%, respectively), while they were less in the others.4. Bacterial source compositionBacterial source composition was different among different glaciers. A majority of the bacteria (44.04%?63.82%) in snowpack were related to cold environments, and MSD (63.82%) held the most. Bacteria from aquatic environments, soils, sediments and other environments represented different proportions in the four glaciers, for example, YL (20.72%) and MZ(14.63%) harbored more soils-related bacteria. Bacteria that had a close relationship to those from polluted environments were significantly more abundant in YL (30.30%) than in the other three glaciers (18.17%?19.69%).Above all, obvious spatial distribution of bacteria community diversity, community composition and bacterial source composition were shown in the four different glaciers. Concentrations of the main ions changed across the four glaciers; bacterial diversity was shaped mainly by local factors, while bacterial community composition was controlled mainly by regional factors. |
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