초록
<P><B>Abstract</B></P><P>The aim of this study was to improve <SMALL>l</SMALL>‐lactic acid production of <I>Lactobacillus thermophilus</I> SRZ50. For this purpose, high efficient heavy‐ion mutagenesis technique was performed using SRZ50 as the original strain. To enhance the screening efficiency for high yield <SMALL>l</SMALL>‐lactic acid producers, a scale‐down from shake flask to microtiter plate was developed. The results showed that 24‐well U‐bottom MTPs could well alternate shake flasks for <I>L. thermophilus</I> cultivation as a scale‐down tool due to its a very good comparability to the shake flasks. Based on this microtiter plate screening method, two high <SMALL>l</SMALL>‐lactic acid productivity mutants, A59 and A69, were successfully screened out, which presented, respectively, 15.8 and 16.2% higher productivities than that of the original strain. Based on fed‐batch fermentation, the A69 mutant can accumulate 114.2 g/L <SMALL>l</SMALL>‐lactic acid at 96 h. Hence, the proposed traditional microbial breeding method with efficient high‐throughput screening assay was proved to be an appropriate strategy to obtain lactic acid‐overproducing strain.</P>