The influence of various metal ions on cell growth and alkaline protease production was evaluated, and the results are demonstrated in Fig. 7. Among the cations tested Ba and Ca ions significantly enhanced the protease production by about 1.6 fold and 1.3 fold compared to the control, respectively. However, most of the other tested ions caused a significant reduction of the enzyme yield particularly at high concentration. Calcium ion has been reported to enhance protease production in several organism. In addition, Ba ion enhanced protease production by Bacillus sp. [43]. It has been reported that these metal ions protected the enzyme from thermal denaturation and maintained its active conformation at the high temperature