Abstract:

The present study was conducted to investigate the possible functions of α-galactosidase derived from Streptococcus alactolyticus strain FGM in Astragalus membranaceus fermentation. The α-galactosidase aga2 gene was cloned with homology-based cloning and its expression during A. membranaceus fermentation was estimated using the determined ideal reference gene ldh through real-time reverse transcription quantitative PCR (RT-qPCR). The results showed that the strain FGM was in exponential growth phase within 6 h and there was a rapid decline of pH value from initial 7.2 to 5.3. The bacteria stable growth phase was post 12 h, pH value was 4.5 and pH value changes were not observed from 48 h to the end of fermentation (72 h). A nucleotide segment of 648 bp was successfully obtained (GenBank No. KC202825) and its highest sequence identity was 98%. Aga2 gene expression was significantly up-regulated (P<0.05) within 24 h and reached a maximum at 24 h (6.04-fold). The aga2 gene expression was only 1.3-fold higher at 36 h. However, it showed a gradual decrease from 36 h to 60 h and was down-regulated at 72 h when it reached a minimum (0.68-fold). The results suggested that α-galactosidase produced by S. alactolyticus strain FGM not only showed some ability to hydrolyze some anti-nutritional factors α-galactosides in A. membranaceus，but also might be responsible for exopolysaccharides biosynthesis indirectly by the Leloir pathway of galactose metabolism.