Fig. 2

Multiple sequence alignment (a) and phylogenetic tree (b) of different bacterial AIs using DNAMAN multiple alignment tool. The amino acid sequence of BCAI (This study) was aligned with other AI sequences from different bacterial sources including B. coagulans 2-6 (BC [2–6]AI, AEH54185.1), B. halodurans (BHAI, WP_010898034.1), B. licheniformis (BLAI, WP_011198012.1), B. subtilis (BSAI, WP_003237722), G. stearothermophilus (GSAI, ABY84698.1), L. fermentum CGMCC2921 (LFAI, 4LQL_A), L. sakei 23 K (LSAI, YP_396468.1), A. acidocaldarius (AAAI, AAY68209.1), P. pentosaceus PC-5 (PPAI, AEM17146.1), T. maritima (TMAI, AKE26215.1), T. neapolitana (TNAI, AAK18729.1). Identical and similar amino acid residues were respectively typed dark blue and purple. The putative catalytic residues which could also bind metal ions were marked with red boxes. Residues that can influence the optimal pH of AIs were marked with blue box. The phylogenetic tree was generated using Neighbor-Joining method on the basis of the alignment above. The numbers in diagram b showed the lengths of branches that represented evolutionary relationships