Analyses of acidophilic bacterial communities and environmental changes using microcosms

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1.The Lake Katanuma, a strongly acid lake, was surveyed during April 2004 to December 2006. The thermal pattern in the lake water showed dimictic. During the stratification period from April to August, oxic water with no hydrogen sulfide was detected in the epilimnion, whereas oxygen depletion and accumulated hydrogen sulfide were prominent in the hypolimnion. Oxic conditions and no hydrogen sulfide were observed in the entire water column during the autumn circulation period.2.Two genus specific oligonucleotide probes were used with fluorescent in situ hybridization (FISH) to measure the biomasses of the genera Acidiphilium and Acidithiobacillus, respectively. The genus Acidiphilium dominated the bacteria community at the stratification period, while both genera dominated at the circulation period.3.We made the microcosms from the lake water of the stratification and circulation periods, respectively. These microcosms were cultured under the following conditions ; 1)dark condition, 2) … More low temperature, 3)low dissolved oxygen, 4)ferrous addition, 5)glucose addition, 6)thiosulfate addition, and 7)control. FISH analysis indicated that the increased abundant of Acidithiobacillus and the decrease of Acidiphilium were observed after 1 week in the microcosms treated with the thiosulfate addition and low temperature. In the microcosms of the other conditions, the biomasses of two genera have not changed.4.Denaturing gradient gel electrophoresis (DGGE) analysis of the microbial community in the microcosms revealed that the genus Acidithiobacillus was consisting of two species, At.caldus and At.albertensis and the genus Acidiphilium was mainly composed of A.acidophilum. Other bacteria genera were not detected by DGGE. Although Acidiphilium species are considered the major representatives of the acidic environments such as the Lake Katanuma, the genus Acidithiobacillus could proliferate under the conditions of sulfide supply or low water temperature during autumn circulation period. Less