Responses of Microorganisms Producing Protease to Heavy Metal Stress

Abstract:

Effects of Pb, Zn, Cu and Cd on growth and enzyme activities of microorganisms such as Bacillus licheniformis 2709, Bacillus subtilis1.398 and Aspergillus usamii 537, which can individually produce alkaline, neutral and acid protease, were studied, respectively. By determining growth and enzyme activities of three bacterial species, as well as analyzing their tolerance and resistance indicators (MTC and MIC) using growth inhibition plate analysis (GIPA) under different heavy metal gradients, results showed that four heavy metals under higher than a special concentration level significantly inhibited growth and enzyme activities of three species. The alkaline protease exhibited greatest adaptability to four heavy metals, next the neutral protease also exhibited certain adaptibilty to Zn and Cd, whereas the acid protease was totally inhibited under any levels of heavy metal concentrations. Three species not only showed great potential to tolerate and resist toxicity of lead and zinc (2.0 mmol/L-6.0 mmol/L), but also showed certain resistance to cadmium (0.5 mmol/L-0.75 mmol/L).