The alkaliphilic bacterium strain Ⅰ-2, which was isolated from soda lakes, was identified as Bacillus akibai by 16S rRNA sequence analysis and suggested to be a new subspecies of genus Bacillus. Two novel thermotolerant alkaline endoglucanases Ⅰ-2-A and Ⅰ-2-B were produced by this alkaliphilic strain. The purified Ⅰ-2-A and Ⅰ-2-B had molecular mass of approximately 60 and 90 kDa, respectively. The optimum pH of Ⅰ-2-A was about 9.0, while that of Ⅰ-2-B was about 8.0. Both enzymes exhibited maximum activity at around 50 °C and were stable up to 50 °C.The two enzymes were resistant to most metal ions and reagents examined. Mass spectrometry analysis indicated that Ⅰ-2-A was probably different from the endoglucanases reported. Ⅰ-2-B showed homology with those of family A5 endoglucanases but low similarity was found in C-terminal amino acid sequence.
A review of the defining chemical properties of soda lakes and pans: An assessment on a large geographic scale of Eurasian inland saline surface waters