Diversity And Spacial Distribution Of Endophytic Bacteria Isolated From Subnival Plants In Upper Reaches Of Urumchi River

Endophytic bacteria are bacteria that reside within plant tissues without doing any harm to the plant, and can be isolated from surface-disinfected or extracted from internal plant tissue. Many bacteria endophytes have been isolated from several tissue types in numerous plant species hitherto. However, very little is known that the diversity, structure composition and functions of endophytes within alpine subnival plants that grow in the extreme environment. Given that above issues, we isolated endophytes from alpine subnival plants growing in the freeze-thaw tundra in border of glacier, where the average temperature is below subzero during the growth period from June to September, by using conventional cultivation method, and determined some physiological characteristics and functions of isolates; at the same time, we also analyzed the abundance, diversity and community structure of endophytes in subnival plants distributed at different altitudes by means of RFLP and 16S rRNA sequence analysis, and made comparisons with microbes from other temperate and cold environments. To our knowledge, our study is the first to describe indigenous endophytic bacteria within alpine subnival plants, which will be essential not only for understanding their ecological roles and the interaction with plants, but also for revealing some phenomena and relationships among glacier, tundra (or soil), plant, microorganism and environment. The major results are as follows:1. A total of 93 isolates were obtained from 20 different subnival plants after phenotypic analysis, and a considerable population size that ranged from 0 to 10⁵ cfu g^-1 FW was monitored. It indicated that there were abundant and diverse endophytic bacteria within alpine subnival plants, and remarkable differences were observed among different subnival plants.2. The results of characteristics determination showed that bacterial endophytes in subnival plants also displayed abundance and diversity in morphology and properties. Most of isolates (70.15%) could produce pigments with the colour of yellow, orange and pink, and 74.58% isolates belonged to psychrotolerant species as they grew well at temperatures from -2-37℃. Moreover, gram-positive bacteria (61.9%) were isolated more frequently than gram-negative bacteria from subnival plants, and most strains (92.9%) were rod shape. These characteristics of endophytes were closely related to their origin and the growth environment of their host plants, i.e., low temperature and strong UV radiation. It also implied that microorganism, being contained in similar environment conditions, whose characteristics were similar, too.3. Based on the analysis of RFLP and 16S rRNA gene sequence, a total of above 22 bacterial genus that vested in α-proteobacteria, γ-proteobacteria, HGC, LGC and CFB was found from subnival plants. Of which, HGC group formed the largest cluster and possessed the highest taxonomic diversity, for which were observed in each plant species and included above 12 genera, accounting for 55.4% in all isolates. Of these, Clavibacter, Rhodococcus and Agreia were the most prevalent genera, α-proteobacteria (17.9%) and γ-proteobacteria (19.6%) were the second large groups inferior to HGC, in which, the members of Sphingomonas and...