塔里木胡杨林可培养胡杨内生细菌多样性与群落结构的时空演变格局

Temporal and spatial patterns of diversity and community structure of culturable endophytic bacteria isolated from Populus euphratica within the rivers of the Tarim basin

阐明塔河,Kiyik河,Ugan河这3条河胡杨内生细菌多样性及群落结构时空演变格局。2011年5月上旬与9月下旬从Kiyik,Ugan古河道和塔河主河道的6个采样位点采集24棵树的胡杨茎秆内存液样,用4种培养基分离纯化了588株胡杨内生细菌。16S r DNA序列分析表明,588株细菌分别属于6大类群:γ-变形菌纲(50.17%),厚壁菌门(34.58%),放线菌门(10.17%),α-变形菌纲(4.24%),拟杆菌门(0.50%),β-变形菌纲(0.34%),47个属,114种。其中有211株菌的16S r DNA相似率<98.0%,它们分别属于19个属的41个物种,是胡杨林本源的潜在新菌种。假单胞菌属(29.76%)和芽孢杆菌属(19.05%)为优势属。与Pseudomonas xinjiangensis相聚类的潜在新种(74株,12.585%)是本源优势菌种。辛普森多样性指数显示,Kiyik河多样性指数为0.931,塔河为0.935;Ugan河最高,为0.969。香农-威纳均匀度指数表明,Ugan河的分布最均匀,均匀度指数为0.8570;塔河次之,为0.8314;Kiyik河最低,为0.7937。时空变化对比分析表明:整体上塔里木胡杨林内生菌群落结构的原生态状态保持较好,较少地遭受到外来优势菌群的侵染。其中,Kiyik古河道的内生菌群落结构保持原生态最好,很少受外来菌群的清洗与取代;Ugan河次之,内生菌群落结构发生了一定程度的变迁;塔河主河道细菌群落结构发生了较大程度的改变,被人类活动带来的外来常见优势菌群生态冲刷的趋势明显。

The aim of this study was to clarify the temporal and spatial patterns of the bacterial diversity and community structure of endophytes isolated from Populus euphratica beside the Tarim, Kiyik （disused） and Ugan （disused） Rivers. The storage liquid in the stem of Populus euphratica stands was gathered as the source for isolation of endophytic bacteria. For each river, eight stands of riparian forest were targeted and the storage liquid from 24 tree stems was sampled in early May and late September 2011. A total of 588 bacterial strains were isolated using four different types of culture media （LB, TSA, NA and King A）. Phylogenetic analysis based on 16S rRNA gene sequences showed that the 588 isolates belonged to Gammaproteobacteria （50.17%）, Firmicutes （34.58%）, Actinobacteria （10.17%）, Alphaproteobacteria （4.24%）, Bacteroidete （0.50%） and Betaproteobacteria （0.34%）, encompassing 47 genera and 114 species. Of those isolates, the 16S rRNA gene sequences of 211 were 〈98% similar to 41 species within 19 genera that could be represented as potentially novel indigenous species. γ-proteobacteria and Firmicutes were the dominant groups in Populus euphratica stem liquid. Pseudomonas and Bacillus were the most widely distributed and predominant genera, accounting for 29.76% and 19.05% of isolates, respectively. The most widely distributed and predominant novel indigenous species had 〈 98% 16S rRNA gene sequence similarity to Pseudomonas xinjiangensis, representing 12.585% of all isolates. The Simpson＇s diversity index of endophytic bacteria from Populus euphratica was highest for the disused Ugan River （0.969）, then lower for the Tarim River （0.935） and the ancient disused Kivik River （0.931）. These data showed that the cultivable endophytic bacteria of Populus euphratica were highly diverse, and similar among the three riparian forest ecosystems. The Shannon-Wiener uniformity index of endophytic bacteria from Populus euphratica from the Ugan River was 0.8570, compared with 0.8314 and 0.7937 for the Tarim and Kiyik Rivers, respectively. The analysis of spatial and temporal variations in the endophytic bacterial community structure of Populus euphratica for the three ecosystems revealed that in general, the community structure of endophytic bacteria from each ecosystem was relatively intact, with some small impact from foreign common dominant bacteria. The bacterial community of the Kiyik River was the least impacted, with the highest abundance of bacterial species and potentially novel indigenous species （1/3.082 and 1/7.55, respectively）, and a minor impact of replacement and cleaning and associated non-indigenous bacterial species. The Ugan River was next highest for abundance of bacterial species and potentially novel indigenous species （1/3.333, 1/12.857） and these values indicate that the bacterial community structure has changed to a certain extent. In contrast, the bacterial community isolated from the Tarim River had been intensively substituted, with the abundance of bacterial species and potentially novel indigenous species greatly decreased to 1/4.282 and 1/20.875, respectively. It is clear that non-indigenous microbes have had a large ecological impact on this bacterial community. Our combined results demonstrate that the endophytic bacterial community structure was influenced by human activity near these three rivers. Human activity stopped for the Kivik and Ugan Rivers after those rivers dried out. The period of time without human activity for the ancient Kiyik and Ugan Rivers has had a positive impact on the community structure of the bacterial population.