Gamma ray mediated mutagenesis of Phialocephala humicola: Effect on kinetics and thermodynamics of -amylase production

Abstract

The current report dealt with the development of the fungus Phialocephala humicolathrough gamma ray treatment for the hyper production of α-amylases, which have diverse industrial applications. Improvement of microbes for the over production of industrial products has been the hallmark of all commercial fermentation processes. Three mutants (M13, M16 and M24) were selected based on the hyper-production of α-amylases. The mutants had gamma ray exposure of 100 and 140 krad (killing rate ≥ 99%). The mutants showed ≥ 2-fold improvement in enzyme production. The effects of inoculum size, temperature, pH and starch concentration on the growth kinetic parameters [µ, td, Yp/x, qp,µm, Ks(x), qpmax, Ks(p)] and thermodynamic parameters [ΔG*(x), ΔH*(x), ΔS*(x) and ΔG*(p), ΔH*(p), ΔS*(p)] were determined. Optimal conditions for the amylase production by the mutants were: inoculum 10% (v/v); pH range of 4-5 and temperature 37°C. The activation energy for cell mass [Ea(x)] of parent, M13, M16 and M24 was 3.095, 15.73, 3.68 and 8.03 kJ mol-1, respectively, whereas their Ea(p) for the enzyme production was 69.42, 22.94, 17.04 and 20.78 kJ mol-1, respectively. The maximum specific rate of cell mass formation (µm) of all mutated strains were greater than that of the parent strain, while specific rate for the maximum product formation (qpmax) of the mutants was about two fold higher than the parental strain. Key words: Activation energy, cell mass estimation, entropy, gibbs free energy growth kinetics.