초록
<P>Microorganisms able to bioconvert <SMALL>DL</SMALL>-2-amino-Δ<SUP>2</SUP>-thiazoline-4-carboxylic acid (<SMALL>DL</SMALL>-ATC) into <SMALL>L</SMALL>-cysteine were originally isolated from 10 soil samples with <SMALL>DL</SMALL>-ATC as the sole nitrogen source. Ninety-seven <SMALL>L</SMALL>-cysteine-producing bacterial strains were screened out and obtained in pure culture. Among them, a strain, designated as HUT-78, was selected as the best producer, with a molar bioconversion rate of 60%. Based on the 16S rRNA gene sequence analysis, this isolate was placed within the genus <I>Pseudomonas</I>. A novel mutant of this strain with a significantly reduced activity of <SMALL>L</SMALL>-cysteine desulfhydrase, a <SMALL>L</SMALL>-cysteine-decomposing enzyme, was derived by UV-mutagenesis. This mutant, designated as mHUT-78, exhibited a 42% increase in <SMALL>L</SMALL>-cysteine producing activity. Moreover, the bioconversion reactions in both the parent and the mutant strain were significantly accelerated by co-overexpression of the two key enzymes, AtcB and AtcC, involved in the bioconversion reaction.</P>