Identification of a strictly aerobic Aeribacillus pallidus strain Gh1 from a hot water spring in Gheynarjeh, Ardebil Province

Water samples were collected from Gheynarjeh hot water spring, around Sabalan Mountain in Ardebil province. One isolate (Gh1), isolated from the hot water spring was chosen for further studies. This selection was based on the isolates ability to grow faster and within the temperature limits chosen. Isolate characteristics were determined by culture on various selective aerobic and anaerobic media, biochemical assays, identification of typical lipids, 16S rDNA sequencing and drawing the phylogenetic tree. Isolate Gh1 was 1μm wide and 3-4μm in length and an endospore-forming non-motile Gram positive bacillus with rectangular terminal spores. The optimal growth temperature was 58-60°C, with Tmin and Tmax at 30°C and 72°C, respectively. The optimal pH for growth was 8.0 and it grew between pH 6 and 10. NaCl concentrations of 0.5–1.0% encouraged growth, but at 2% NaCl, growth was inhibited. The only carbohydrate source with a positive effect on bacterial growth was starch. The isolate exhibited amylolytic as well as gelatinolytic, catalase and oxidase activities. The isolate was aerobic and no growth was observed on anaerobic medium. Cell wall fatty acid analysis showed the presence of phosphatidyl ethanolamine, diphosphatidyl glycerol, phosphatidyl glycerol and several unidentified lipids and phospholipids. Diaminopimelic acid could not be detected in the peptidoglycan. The 16S rDNA sequence analysis exhibited 99.72% identity with Aeribacillus pallidus. Other important characteristics, such as movement and anaerobiosis were different from those previously reported isolates. In addition, the results showed that the presence/absence of phosphatidyl ethanolamine cannot be used as a variable for differentiating between Geobacillus and Aeribacillus.