Dominant Bacteria and Biomass in the Kuytun 51 Glacier

Abstract

Dominant bacteria in the different habitats in the Kuytun 51 Glacier were investigated using a 16S rRNA gene clone library sequencing technique. Results showed diverse bacteria on the glacial surface, with the dominant phyla being Proteobacteria, Cyanobacteria, and Bacteroidetes. UniFrac data showed distinct community patterns between the Kuytun and Himalayan Rongbuk glaciers.

Comparisons of geographically distinct glaciers worldwide have shown a great variation in microbial biomass and community structure (6, 8, 15, 18, 22, 34, 36). The variability is largely controlled by climatic and environmental factors, including geographic location (4, 12, 19, 24), wind direction, wind speed, light intensity, and availability of nutrients and liquid water (5, 6, 9, 13, 19, 24). There is some limited evidence of biogeographic effects on the distribution of microorganisms in the geographically different glaciers (7, 15, 25, 34, 36). However, main factors driving the dynamics of microbial community in glacial systems remain unclear.

The Kuytun 51 Glacier is a typical cold-based subcontinental glacier (11). The microbial communities in subcontinental glaciers have not been studied in detail, as there have been only a few reports on continental and polar glaciers (7, 16, 22, 23). To initially investigate the biogeographic effects on the distribution of microorganisms in glacial ice, six 16S rRNA gene libraries were established from the Kuytun 51 Glacier. Bacterial-community comparison was conducted among the Kuytun 51, John Evans (Canada) (22), Alaska Bench (22), and Himalayan Rongbuk (16) glaciers.

The glacial samples were obtained with extreme caution from the different habitats, solid ice, firn, and snow, at the terminus, middle, and top of the Kuytun 51 Glacier (84°24′E, 43°43′N) in the Tianshan Mountains in 2005. Numbers of live cells and total biomass in the melt water were determined with a flow cytometer in combination with cell marker propidium iodide and carboxyfluorescein diacetate by following the method of Amor et al. (3), except for cell staining for 15 min at 25°C. DNA nucleic acids were extracted from a portion (400 ml) of the melt water filtered through a sterile 0.22-μm-pore-size filter unit (Millipore) by following the protocols described by Zhou et al. (38). A neighbor-joining (28) phylogeny for the ClustalX (30) aligned sequences was constructed using MEGA 4.0 (27) with the maximum composite likelihood method (see the detailed methods in the supplemental material).

The Kuytun 51 Glacier contains a relatively large biomass, ranging from 7.27 × 10⁴ to 1.29 × 10⁶ cells/ml and 1.14 × 10³ to 2.69 × 10⁴ cells/ml for the total biomass and live biomass, respectively (Table 1); these numbers are higher than in most glaciers worldwide (Table 2). This could be attributed to the fact that Kuytun 51 Glacier is located near (within about 10 km of) human settlements and surrounded by vast deserts: the Gobi, Muyun Kum, Kyzyl Kum, and Kara Kum deserts (14). The frequent dust storm outbreaks that emerge in and around the arid and semiarid regions possibly carry a large number of microbes associated with dust onto the glacier via prevalent westerly winds (10, 14, 33). Biomass is generally higher in the mountainous glaciers than in the polar glaciers, which are far away and little influenced by the activities of human beings (Table 2) (8, 34). However, there are some exceptions, including low biomass in the Malan Glacier (35) and high biomass in the “silty” ice from the GISP 2 ice core (18). This may be attributed to the specific climatic and environmental conditions and local habitats. More data are necessary before definitive conclusions can be drawn because of different methods used in the estimation of biomass.

TABLE 1.

Bacterial biomasses in the different habitats of the Kuytun 51 Glacier

Zone	Altitude (m above sea level)	Description	Total no. of cells (104 cells ml−1)	No. of live cells (102 cells ml−1)	% of cells that were live
Dry snow	3,725		16.96	11.45	0.68
Firn	3,601	Firn zonea	105.40 ± 23.54	232.34 ± 36.37	2.20 ± 0.88
		White	81.86 ± 20.36	195.97 ± 30.78	2.39 ± 1.20
		Brown	128.93 ± 27.14	268.71 ± 40.32	2.08 ± 0.32
Ablation	3,505	Ablation zoneb	34.92 ± 24.59	77.72 ± 51.26	2.22 ± 0.33
		Ice, H2O, and particles	43.18	94.9	2.2
		Ice	54.32	118.18	2.18
		H2O	7.27	20.07	2.76

^aThe average value was calculated by the analysis of three white and three brown snow samples collected in the firn zone of the glacial surface.

^bThe average value was calculated by the analysis of ice, ice-water particles, and water samples collected in the ablation zone.

TABLE 2.

Biomass comparison among ice samples from the Kuytun 51 Glacier and other glaciers worldwide

Glacier	Location	Altitude (m above sea level)	Glacial type	Total biomass (104 cells/ml)	Live biomassa	Reference
Kuytun Tienshan Mt.	84°24′E	3,500-4,000	Subcontinental	7.3-129	11.4 × 102-269 × 102 cells/ml	This study
	43°43′N
Rongbuk Hymalaya	28°01′N	6,000-8,000	Continental	2.1-90.4	0.1-5 CFU/ml	16, 34
	86°57′E
Guoqu Geladandong	33°34′N	6,621	Continental	0.3-83 (ice core)	ND	15
	91°10′E
Palong	29°14′N	4,618-5,974	Marine	0.68-37.2	ND	15
	96°55′E
Kongsvege	78°56′N			1-20		2
	11°52′E
Muztag Ata	38°17′N	6,350	Continental	0.2-21.7 (ice core)	0-1.04 CFU/ml	32
	75°04′E
Guliya	35°21′N	6,200	Subcontinental	1 (ice core)	0.07-1.8 CFU/ml	8
	81°31′E
Malan	35°50′N	5,680	Continent	0.005-0.04 (ice core)	<1-0.85 CFU/ml	35
	90°40′E
Puruogangri	33°44′N	6,000	Subcontinental	2.56-25.5 (ice core)	0-7.6 CFU/ml	37
	89°20′E
Bench (Alaska)	61.03°N	950-1,600	Subglacial	6.6-37	ND	22
	145.7°W
John Evans (Arctic)	79°40′N	100-1,500	Polythermal	ND	1-10 CFU/ml	22
	74°00′W
Antarctica	78°27′S	3,500	Polar	0.003-0.83		1
	106°48′E
GISP2	72°35′N	3,203	Polar	6,100-9,100 (base ice)	ND	18
Greenland	37°38′W
South Pole	90°S	2,835	Polar	0.02-0.5		6
Taylor Dome, Antarctica	77°47′S	2,365	Polar		∼10 CFU	7
	158°43′E

^aND, no determination.

All 112 16S rRNA gene sequences obtained from the Kuytun 51 Glacier were >97% similar to known species from the different environments. They fell into 30 subphyla within 10 phyla: Alpha-, Beta-, Delta-, and Gammaproteobacteria, Bacteroidetes, Chloroflexi, Firmicutes, Actinobacteria, Deinococcales, and Cyanobacteria (see the supplemental material). There was an apparent difference in the phylogenetic distributions of bacteria in the glacier (Fig. 1). Proteobacteria were the most dominant bacteria, Bacteroidetes and Cyanobacteria were the second-most-common bacteria on the glacier surface, and Actinobacteria were present along the glacier surface, although they accounted for a small proportion of the total clones. Only a few clones belonging to the families Chloroflexi and Deinococcales and Firmicutes were found from the ice and firn niches.

FIG. 1.

Clonal frequency of the main phylogenetic groups based on the BLAST result of 16S rRNA gene clone sequencing in a single library.

The Kuytun Glacier bacteria represented two distinct metabolic types, including phototrophs and heterotrophs. Cyanobacteria were the dominant phototrophs across the glacial surface and closely related to the known species in four subgroups: Phormidium, Pseudanabaena, and Oscillatoria spp. and Stephanopyxidaceae. These phototrophic Cyanobacteria have frequently been reported from geographically different glaciers, such as the Alaska (26), Chile Tyndall (24), Svalbard (23), and Antarctic (7, 19, 29) glaciers. However, only one cyanobacterial clone has been reported from the Rongbuk Glacier (16). These results suggest that Cyanobacteria are very common in some glaciers but rare in other glaciers, which can be attributed to the possibly different sources of microbial loads on the glacier and the specific selection effect of local climatic and environmental conditions on microorganisms. The highly pigmented and structured biofilms may allow the Cyanobacteria to tolerate extreme environments and dominate in the glaciers (31).

Betaproteobacteria and Bacteroidetes are the most common phyla in the Kuytung 51 Glacier (Fig. 1), which is consistent with previous reports on the bacterial communities in glaciers (4, 15, 16, 23). This is possibly attributed to their tolerance to oligotrophic environments (21) and a wide spectrum of substrate range in low-nutrient media (20). Bacteroidetes are able to produce copious amounts of extracellular polymeric substances on surfaces and have high catabolic ability for complex and more recalcitrant organic matter (4).

Also of significance are the apparent differences in dominant bacterial community compositions among the geographically distinct glaciers around the world (Fig. 2a and b). When subjected to UniFrac analysis, the dominant bacterial communities from the same glacier form distinct clusters from other glaciers (Fig. 2b). This promotes the idea of biogeography as an important factor with regard to microbial community structure.

FIG. 2.

Hierarchical clustering showing the overall phylogenetic distances between the bacterial communities on the Kuytun glacial surface (this study) and from John Evans Glacier, Canada (22), Alaska Bench Glacier (22), and East Rongbuk Glacier north of the Himalayas (16). (a) Comparison of communities among the Kuytun 51 Glacier, John Evans Glacier, Bench Glacier, and Rongbuk Glacier; (b) community comparison between the Kuytun 51 Glacier and Rongbuk Glacier (sequence KuyT-ice-3 with a later portion of the 16S rRNA gene was removed from the phylogenetic tree list). Distances were estimated with the weighted UniFrac algorithm (17). A sequence jackknifing technique was applied to each cluster to determine the sensitivity of the relationships to sample size.

Nucleotide sequence accession numbers.

The GenBank accession numbers of the cloned sequences described in this study are EU263676 to EU263787.