湖北神农架大九湖泥炭地泥炭藓共生细菌群落分析

对采自湖北神农架大九湖泥炭地泥炭藓(Sphagnum palustre)样品进行了不同预处理,之后提取微生物基因组DNA,构建克隆文库进而对泥炭藓共生菌的群落结构进行分析。菌落培养实验和荧光定量PCR结果显示,双氧水能杀死泥炭藓表面附生的微生物及破坏部分DNA,为研究泥炭藓内共生细菌提供一定的途径。群落组成分析结果表明双氧水处理后,所获得的细菌克隆文库的群落特征发生了改变,主要表现在细菌种类的减少及各菌门所占比率的变化上: NTX-0中酸杆菌门(Acidobacteria)和变形杆菌门(Proteaobacteria)百分比含量分别位居第一和第二,而经过双氧水进行表面除菌后NTX-0-degerming中变形菌门(Proteobacteria)占了绝对优势; 而在NTX-2-degerming中,蓝细菌门(Cyanobacteria)占绝对主导地位,细菌的群落多样性明显降低,细菌种类减少。系统发育分析表明与泥炭藓内共生的细菌一方面能适应大九湖泥炭湿地酸性、贫营养的环境,另一方面能为泥炭藓提供碳源、氮源,从而参与泥炭湿地的元素循环。尤其值得注意的是在内共生菌中发现了Ⅱ型甲烷氧化菌,证实了甲烷氧化菌与泥炭藓的内共生关系,暗示着这类细菌通过自身的代谢进而影响全球碳循环的潜在意义。此外,首次报道了利用细菌的通用引物扩增出了大量泥炭藓叶绿体的序列,这可能为叶绿体内共生学说提供佐证。

SYMBIOTIC BACTERIAL COMMUNITY OF Sphagnum palustre IN DAJIUHU PEATLAND,HUBEI,P.R.CHINA

Sphagnum palustre is the dominant plant in many oligotrophic peatlands and its growth is closely related to the environmental conditions as well as to the endosymbiotic bacteria.To date endophytes of S.palustre and their potential role in carbon cycles are not well understood.To investigate the endosymbiotic bacterial communities and their possible ecological function in peatland ecosystem,Sphagnum samples were collected from the Dajiuhu peatland,which locates in the intermountain basin(1757m a.s.l.; 31°28'50″N, 110°00'90″E),north western Hubei Province,with an area of about 16km2.Fresh green parts of S.palustre were treated with and without hydrogen peroxide and were subjected to DNA extraction and clone library constructions subsequently.The treated samples were designated as NTX-0-degerming and NTX-2-degerming,corresponding to the untreated samples of NTX-0 and NTX-2 respectively. Viable counting and quantitive analysis of 16S rRNA conformed that hydrogen peroxide can effectively kill the epizoic bacteria of S.palustre and destroyed their DNA partially.Even though some similarities were observed between the bacterial compositions of the hydrogen peroxide treated and untreated samples,bacterial community structures obviously changed as indicated by clone library analysis.For example Acidobacteria and Proteaobacteria are dominant in NTX-0 while in NTX-0-degerming Proteaobacteria became the only dominant group.Phylogenetic analysis indicated most of the endosymbiotic bacteria can adapt to the acidic and oligotrophic conditions of Dajiuhu peatland.Some of them can degrade the toxin and other pollutants.Others can fix N2 or provide CO2 for the growth of S.Palustre. The detection of type Ⅱ methanotroph in the treated S.palustre samples demonstrated the ubiquitous endosymbiosis of methanotroph and S.palustre.Our data shed light on the understanding of the symbiotic microbial community and microbe-mediated elemental cycles in peatlands.Interestingly abundant Sphagnum chloroplasts DNA was detected despite of bacterial specific primers were used.This might mount evidence for the endosymbiotic hypothesis of chloroplasts.