Diversity analysis of bacterial community in a strongly acid lake

1. 1998年2月至2000年12月对Katanuma湖进行了调查。夏季，由于湖底火山热供给的影响，湖泊水体热格局呈现二分形，而中、次阴离子的温差相对较小。在夏季分层过程中，1998年和1999年观测到全湖水体短期内的偶发环流。因此，低阴离子中高浓度硫化氢和缺氧的状况遍及整个湖泊。从9月到12月，湖水从表面到底部循环。然而，在2000年，没有观察到夏季停滞期间的短期环流。短期环流的发生取决于当年的天气。细菌生物量垂直分布的变化受湖水停滞和循环的季节变化的影响。分层期丝状菌密度高，短杆状菌丰度低。9月翻转后，全湖水体丝状菌生物量下降，短杆菌生物量增加。16S rRNA基因序列的系统发育分析表明，从湖水中分离的菌株分别属于α亚门和γ亚门。α变形杆菌属菌株的部分序列与藤沢甲杆菌的部分序列密切相关。伽玛变形菌与溶酶杆菌和铁氧化型养石菌的序列有明显的相似性，表明这些菌株可能具有自养作用。利用直接从湖泊水体中提取的rDNA序列进行系统发育分析还需要进一步的研究。

1. The Lake Katanuma, a strongly acid lake, was surveyed during February 1998 to December 2000. The thermal pattern in the lake water showed dimictic, whereas the difference in water temperature between epilimnion and hypolimnion in summer was relatively small due to the volcanic heat supply from the lake bottom. During stratification in summer, the occasional circulations of whole lake water in a short term were observed in 1998 and 1999. Consequently, the condition of high concentration of hydrogen sulfide and oxygen depletion in hypolimnion spread over the whole lake. From September to December, the lake water circulated from the surface to the bottom. In 2000, however, the short-term circulation during summer stagnation was not observed. The occurrence of short-term circulations depends on the weather of that year.2. The changes in the vertical distribution of bacterial biomass were influenced by the seasonal change in stagnation and circulation of lake water. In stratification period, high densities of filamentous bacteria and low abundance of short rods were observed. After the overturn in September, the biomass of filamentous bacteria decreased and that of short rods increased in the whole lake water.3. Phylogenetic analyses of the sequences of 16S rRNA gene show that the strains isolated from lake water fell into proteobacteria alpha subdivision and gamma subdivision. The partial sequences of the strains belonging to alpha proteobacteria were closely related to that of Methylobacterium fujisawaense. The strains of gamma proteobacteria show distinct similarities to sequences of Lysobacter enzymogenes and the iron oxidizing lithotrophs, suggesting that these strains may act as autotrophs.Further studies in terms of the phylogenetic analyses by rDNA sequences directly retrieved from the lake water are needed.