Abstract: This work aims to breed a strain yielding high L-isoleucine by mutagenesis,and explore the optimal fermentation conditions for the mutant strain. The original strain Brevibacterium flavum I-12 was mutagenized by conventional chemical mutagenesis and atmospheric and room temperature plasma（ARTP）biological breeding system. A mutant strain having high resistance to 2-thiazolyl alanine（2-TA）and sulfaguanidine（SG）and capable of rapid growth on a succinic acid plate was selected. Subsequently,the response surface design based on the single factor experiment was used to optimize the optimal parameter level of the shake flask fermentation medium components for the target mutant strain. Results showed that a strain producing L-isoleucine was obtained after multiple rounds of random mutagenesis and screening,which was resistant to 40 g/L of 2-TA and 5 g/L of SG and rapidly grew on the medium with succinate as the sole carbon source,and designated as B. flavum TA-6. The L-isoleucine production by this mutant strain reached 26.2±0.5 g/L,which was 44.75% higher than that by the original strain（18.1±0.5 g/L）;while the accumulations of side product L-valine and L-leucine significantly reduced. The L-isoleucine production increased to 27.8±0.5 g/L after optimizing the fermentation conditions by response surface method,which was 6.1% higher than that before optimization. In conclusion,a strain yielding high L-isoleucine but producing low other acids,TA-6,is obtained by conventional chemical mutagenesis and ARTP biological breeding system,thus it has potential production and application value in L-isoleucine fermentation industry.

Key words: L-isoleucine, chemical mutagenesis, atmospheric pressure room temperature plasma, resistance screening