Fig. 2

a Response surface curve showing the effects of pH and peptone on the protease activity of B. subtilis IND19 in SSF using cow dung substrate. b Response surface curve showing the effects of pH and NaH2PO4 on the protease activity of B. subtilis IND19 in SSF using cow dung substrate. c Response surface curve showing the effects of peptone and NaH2PO4 on the protease activity of B. subtilis IND19 in SSF using cow dung substrate