Shu-Rong Xiang

16S rRNA Sequences and Differences in Bacteria Isolated from the Muztag Ata Glacier at Increasing Depths

ABSTRACT Small subunit 16S rRNA sequences, growth temperatures, and phylogenetic relationships have been established for 129 bacterial isolates recovered under aerobic growth conditions from different regions of a 22-m ice core from the Muztag Ata Mountain glacier on the Pamirs Plateau (China). Only 11% were psychrophiles (grew at 2°C or −2°C up to ∼20°C), although the majority (82%) were psychrotolerant (grew at 2°C or −2°C up to 37°C). The majority of the isolates had 16S rRNA sequences similar to previously determined sequences, ranging from 85% to 100% identical to database sequences. Based on their 16S rRNA sequences, 42.6% of the isolates were high-G+C (HGC) gram-positive bacteria, 23.3% wereγ -Proteobacteria, 14.7% were α-Proteobacteria, 14.7% were Flavobacteria, and 4.7% were low-G+C (LGC) gram-positive bacteria. There were clear differences in the depth distribution, with Proteobacteria, HGC/Cytophaga-Flavobacterium-Bacteroides (CFB), Proteobacteria, LGC/CFB/HGC, Cryobacterium psychrophilum, HGC/CFB, Proteobacteria/HGC/CFB, and HGC/CFB being the predominant isolates from ice that originated from 2.7 to 3.8, 6.2, 7.5, 8.3, 9.0, 9.7, 12.5, and 15.3 m below the surface, respectively. This layered distribution of bacterial isolates presumably reflects both differences in bacteria inhabiting the glaciers surface, differences in bacteria deposited serendipitously on the glaciers surface by wind and snowfall, and nutrient availability within the ice.

Deposition and postdeposition mechanisms as possible drivers of microbial population variability in glacier ice

Glaciers accumulate airborne microorganisms year by year and thus are good archives of microbial communities and their relationship to climatic and environmental changes. Hypotheses have focused on two possible drivers of microbial community composition in glacier systems. One is aeolian deposition, in which the microbial load by aerosol, dust, and precipitation events directly determines the amount and composition of microbial species in glacier ice. The other is postdepositional selection, in which the metabolic activity in surface snow causes microbial community shifts in glacier ice. An additional possibility is that both processes occur simultaneously. Aeolian deposition initially establishes a microbial community in the ice, whereas postdeposition selection strengthens the deposition patterns of microorganisms with the development of tolerant species in surface snow, resulting in varying structures of microbial communities with depth. In this minireview, we examine these postulations through an analysis of physical-chemical and biological parameters from the Malan and Vostok ice cores, and the Kuytun 51 Glacial surface and deep snow. We discuss these and other recent results in the context of the hypothesized mechanisms driving microbial community succession in glaciers. We explore our current gaps in knowledge and point out future directions for research on microorganisms in glacial ecosystems.

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.

Bacterial diversity in Malan ice core from the Tibetan Plateau.

Three ice core samples were collected from the Malan ice core drilled from the Tibetan Plateau, and three 16S rDNA clone libraries by direct amplification from the ice-melted water were established. Ninety-four clones containing bacterial 16S rDNA inserts were selected. According to restriction fragmentlength polymorphism analysis, 11 clones were unique in the library from which they were obtained and used for partial sequence and phylogenetic analysis, and compared with 8 reported sequences from the same ice core at depth 70 m. Differences among the samples were apparent in clone libraries. The phylotypes were dominated by theProteobacteria group,Acinetobacter sp. andCytophaga-Flavobacterium-Bacteroides (CFB) group. They accounted for 92.5 % (Proteobacteria), 100 % (Acinetobacter sp.), 34.4 % (CFB) and 100 % (β-Proteobacteria) in the clone libraries from the samples at ice depths 35, 64, 70, and 82 m, respectively. TheAcinetobacter sp. was only found in the deposition at ice depth 82 m and closely clustered with γ-Proteobacteria. Two members (Malan A-21 and 101) of α-Proteobacteria from the sample of 35 m and two (Malan B-26 and 48) of β-Proteobacteria of 64 m were loosely clustered (<95 %similarity) with known bacteria, represented new genera in ice bacteria.

Change of bacterial community in the Malan ice core and its relation to climate and environment

In order to understand the relationship between the community structure of bacteria in ice core and the past climate and environment, we initiated the study on the microorganisms in the three selected ice samples from the Malan ice core drilled from the Tibetan Plateau. The 16S ribosomal DNA (rDNA) molecules were directly amplified from the melt water samples, and three 16S rDNA clone libraries were established. Among 94 positive clones, eleven clones with unique restriction pattern were used for partial sequence and compared with eight reported sequences from the same ice core. The phylotypes were divided into 5 groups: alpha, beta, gamma proteobacteria; CFB, and other eubacteria group. Among them, there were many “typical Malan glacial bacteria” pertaining to psychrophilies and new bacteria found in the ice core. At a longer time scale, the concentration distribution of “typical Malan glacial bacteria” with depth showed negative correlation with temperature variations and was coincident with dirty layer. It implied the influence of temperature on the microbial record through impact on the concentrations of the “typical Malan glacial bacteria”. In addition, the nutrition contained in ice was another important factor controlling the distribution of microbial population in ice core section. Moreover, the result displayed an apparent layer distribution of bacterial community in the ice core section, which reflected the microbial response to the past climatic and environmental conditions at the time of deposition.

Formate and acetate records in the Muztagata ice core,Northwest Tibetan Plateau

Formate and acetate concentrations are measured in a 22.56 m-depth ice core recovered in Mt. Muztagata Glacier, northwest Tibetan Plateau. The mean concentrations for formate and acetate in this ice core are 186.6±160.1 and 136.4±133.9 ng/g, respectively. Study shows that there is a positive correlation between formate and nitrate, suggesting both continental origins. However, no significant relationship has been found between formate and acetate, though they both have obvious periodical variations. Because Mt. Muztagata lies in the mid-latitude and is correlative to the nearby human activities, formate and acetate concentrations are higher than those in Greenland and Antarctica. During recent decades, the increase of formate concentration in the Muztagata ice core and formaldehyde production shows a close correlation. We preliminarily presume that the high formate concentration in the Muztagata ice core is concerned with the thriving of house decoration in which excess formaldehyde was used.

Changes of the Bacterial Abundance and Communities in Shallow Ice Cores from Dunde and Muztagata Glaciers, Western China

In this study, six bacterial community structures were analyzed from the Dunde ice core (9.5-m-long) using 16S rRNA gene cloning library technology. Compared to the Muztagata mountain ice core (37-m-long), the Dunde ice core has different dominant community structures, with five genus-related groups Blastococcus sp./Propionibacterium, Cryobacterium-related., Flavobacterium sp., Pedobacter sp., and Polaromas sp. that are frequently found in the six tested ice layers from 1990 to 2000. Live and total microbial density patterns were examined and related to the dynamics of physical-chemical parameters, mineral particle concentrations, and stable isotopic ratios in the precipitations collected from both Muztagata and Dunde ice cores. The Muztagata ice core revealed seasonal response patterns for both live and total cell density, with high cell density occurring in the warming spring and summer months indicated by the proxy value of the stable isotopic ratios. Seasonal analysis of live cell density for the Dunde ice core was not successful due to the limitations of sampling resolution. Both ice cores showed that the cell density peaks were frequently associated with high concentrations of particles. A comparison of microbial communities in the Dunde and Muztagata glaciers showed that similar taxonomic members exist in the related ice cores, but the composition of the prevalent genus-related groups is largely different between the two geographically different glaciers. This indicates that the micro-biogeography associated with geographic differences was mainly influenced by a few dominant taxonomic groups.