Characterization of Microaerobacter geothermalis gen. nov., sp. nov., a novel microaerophilic, nitrate- and nitrite-reducing thermophilic bacterium isolated from a terrestrial hot spring in Tunisia

摘要

A novel thermophilic anaerobic and microaerophilic bacterium (optimal growth in the presence of 5-10% O_2), strain Nad S1~T was isolated from the terrestrial hot spring of Hammam Sidi Jdidi, Nabeul, Tunisia. Cells were motile rods having a Gram-positive cell wall structure. Strain Nad S1~T grew optimally at 55°C (range 37-70°C). Optimum pH for growth was 6.5-7.0. It was halotolerant growing with NaCl up to 7% (optimum concentration 1. 5-3.0%). It grew chemoorganotrophically on various carbohydrates, organic-acids and amino-acids as energy sources, or chemolithotrophically on H_2 using nitrate, as terminal electron acceptor. Beside oxygen (under microaerobic conditions) and nitrate, nitrite was also used. Nitrate was completely reduced to N_2. No fermentation occurred. The genomic DNA G + C content was 41.8 mol%. Based on 16S rRNA gene sequence analysis, strain Nad S1~T belongs to the Bacillaceae family within the class 'Bacilli'. Because of its phylogenetic and phenotypic characteristics, we propose this isolate to be assigned as a novel genus and a novel species within the domain Bacteria, Microaerobacter geothermalis gen. nov., sp. nov. The type strain is Nad S1~T (=DSM 22679~T =JCM 16213~T).