Improvement in enzyme productivities from mold cultivations using the liquid-phase oxygen supply strategy

Cultivations of Aspergillus niger cells in which oxygen was provided throug h the liquid-phase oxygen supply strategy (which involves the need-based de composition of H2O2 pulses to yield the necessary oxygen) were studied. Con centrations of H2O2 in the range of 1 to 5 mM were found to be suitable for use in cultivations. The growth rate constant of 0.17 h(-1) obtained in th e H2O2-based cultivation, was comparable to that obtained in the cultivatio n with aeration; however, the maximum cell concentration in the H2O2-based cultivation was 124% of that obtained in cultivation with aeration. Maximum concentrations of catalase, protease and glucose oxidase obtained in the H 2O2-based cultivation, were 240%, 172%, and 124% respectively, of those obt ained in the cultivation with aeration. Further, the specific enzyme levels (units per gram cell) of catalase and protease obtained in the H2O2-based cultivation were 172% and 156% of those obtained in the cultivation with ae ration, whereas, the specific glucose oxidase levels were comparable. In ad dition, the oxygen profiles inside the pellets of A. niger during both the modes of oxygen supply were described using mathematical models. Studies to elucidate the mechanism of oxygen availability showed that the decompositi on of the H2O2 supplied in the extracellular space occurred intracellularly , as well as extracellularly, to yield oxygen. Also, the proton motive forc e (PMF) was found to be involved in the process of oxygen availability from H2O2 to A. niger cells.