Mutation breeding of nuclease pi production in Penicillium citrinum by low-energy ion beam implantation

摘要

Nuclease pl is an important enzyme in the nucleotide industry that is used to hydrolyze nucleic acid into nucleotides. To improve enzyme activity, Penicillium citrinum, a nuclease pl producing strain, was mutated by low-energy Nitrogen ion beam implantation at an energy level of 15 keV and a dose ranging from 1 x 10~(l5)-1 × 10~(16) ions/cm~2. The mutant strain designated as N409 was obtained with a high yield of nuclease pl. The activity of nuclease pl was 421 U/mL from the mutant strain N409, which was increased by 86% compared with the control. The fermentation kinetics of nuclease pl by the mutant strain N409 was studied in a 30 L external airlifting bioreactor. A model was proposed using the logistic equation for microbial growth, the Luedeking-Piret equation for product formation and a Luedeking-Piret-like equation for substrate uptake. The results predicted from the model were in good agreement with the experimental observations.