An oxalate decarboxylase-like cupin domain containing protein is involved in imparting acid stress tolerance in Bacillus amyloliquefaciens MBNC.

We report here the structural and functional properties of an oxalate decarboxylase (OxDC)-like cupin domain-containing protein of Bacillus amyloliquefaciens MBNC and its role in imparting tolerance to acid stress conditions. Quantitative real-time PCR (qPCR) analysis revealed 32-fold and 20-fold upregulation of the target gene [(OxDC')cupin] under acetic acid stress and hydrochloric acid stress, respectively, indicating its association with the acid stress response. Bacterial cells with targeted inactivation of the (OxDC')cupin gene using the pMUTIN4 vector system showed decreased growth and survival rate in acidic pH, with drastically reduced exopolysaccharide production. In Silico protein-protein interaction studies revealed seven genes (viz. glmS, nagA, nagB, tuaF, tuaF, gcvT, and ykgA) related to cell wall biosynthesis and biofilm production to interact with OxDC-like cupin domain containing protein. While all these seven genes were upregulated in B. amyloliquefaciens MBNC after 6 h of exposure to pH 4.5, the mutant cells containing the inactivated (OxDC')cupin gene displayed significantly lower expression (RQ: 0.001-0.02) (compared to the wild-type cells) in both neutral and acidic pH. Our results indicate that the OxDC-like cupin domain containing protein is necessary for cell wall biosynthesis and biofilm production in Bacillus amyloliquefaciens MBNC for survival in acid-stress conditions.