Study On The Diversity Of Culturable Bacteria From Meltwater And Subgalical Sediments In Tianshan No.1 Glacier

Object: The largest part of the Earth’s microbial biomass is stored in cold environments, which represent almost untapped reservoirs species, process, and genes. However, to date, knowledge of the origin, maintenance and distribution of diversity on terrestrial microorganisms remains limited.Cold environmnets represent the majority of the biosphere on Earth and have been successfully colonized by psychrophilic microorganisms that are able to thrive at low temperature and to survive and even maintain metabolic activity at subzero temperatures. The large part of the Earth’s microbial biomass is stored in cold environments, which represent almost untapped reservoirs of novel species, processes, and genes. Forefields of receding glacier are pristine and sensitive environments representing natural chronosequences and the spatial heterogeneities. One consequence is the acceleration of glacier retreat, exposing new habitats that are colonized by microorganisms whose diversity and function are unknown. Thus, these glacier forefields provide excellent opportunities to study microbial succession, biogeochemical weathering processes, and the conversion of glacial till into fertile soil along the chronosequence in regionally defined landscape.Methods: In this study, culture-dependent approaches were used to investigation the bacterial diversity of sediment collected from glacier No.1 in the Tianshan Mountains. Those isolated bacterias with low temperature tolerance were screened out and the optimum growth temperature and physiology biochemistry experiments were also measured. The phylogenetic status of those Lactic acid bacteria with low temperature resistant were identified based on 16 S r RNA gene sequence. BOX primers was used to preform the rep-PCR, the strains with highly homologous of 16 S r RNA were future investigated, A preliminary study on the susceptibility of the isolated strains were also preformed with the paper method.Results:By use the five screening media, screening of bacteria from melt water and sediments of the bottom layer of the Glacier No.1 in the Tianshan Mountains, led to the isolation of nearly 116 aerobic and psycrotrophic bacteria, which were formed pigmented colonies, such as white(31strains), yellow(40 strains), beige(6 strains), orange(9 strains), red(17 strains) and pink(3strains). Most of the isolates(71.25%) were psychrotolerant with upper growth temperature limit between 25 and 37℃. Representatives of the 116 isolates varied in their tolerated to Na Cl(2-10%) and in the growth of p H range(3.0-13.0). The phylogenetic analyses of 116 representative r RNA gene sequences showed that the strains belonged to six major phylogenetic groups: theα-Proteobacteria, β-Proteobacteria, γ-Proteobacteria, Actinobacteria, Firmicutes and the Bacteroidetes, in which consisted of 28 genera in the subglacial of the glacier No.1. The most abundant and diverse isolates were within the γ-Proteobacteria cluster(28.5%) that had exhibited unique phenotypic properties.1. Biochemical characteristics of the isolates were tested using the Bergey’s Manual of Determinative Bacteriology with 7 kinds of biochemical tests, the results indicated that most of cultures(83.75%) were positive for production of ammonia test and V-P, almost half of isolates were positive for Indole test and Gelation liquefaction, only 8.5% of the strains were positive for M.R, 27.5% for Nitrate reduction. The fact that the 16 S r RNA gene sequences of cultured bacteria closely, but were biochemical characteristics markedly different.3. Among 116 isolates produced a great variety of extracellular hydrolytic enzymes. A total of 47,46, 23, 22 strains produced proteases, lipases, celluass, amylase, respectively. Most of produced enzymes strains showed optimum temperature for growth was 24℃, highest salt tolerance at 6%,optimum p H for growth was p H6-7. The phylogenetic analyses of produced enzymes strains 16 S r RNA gene sequences showed that the strains belonged to six major phylogenetic groups,including 24 genera. The most abundant strains produced proteases, lipases, celluass, amylase were affiliated with genuses Pseudomonas, Flavobacterium, Rhodococcus, Bacillus,Brevundimonas.4. When the isolates(80 strains) were subjected to antibiotic screening, it is interesting that all strains were resistant to mono-or multiple antibiotics tested. Nalidixic acid-, chloramphenicol- and bacitracin-resistances were most frequently among these strains(97.5%), followed by penicillin-,Cefotaxime- and erythromycin-resistances reached similar levels(95.0, 91.2, and 90.0%). On the contrary, only 43.8% of the tested strains were resistant to neomycin.We observed that the sensitivity of isolates toward varied antibiotics was visible difference, but on the whole, the antibiotic resistance of strains is high in the present study.