초록
<P><B>ABSTRACT</B></P><P>Poly lactic acid (PLA) based plastics is renewable, bio‐based, and biodegradable. Although present day PLA is composed of mainly L‐LA, an L‐ and D‐ LA copolymer is expected to improve the quality of PLA and expand its use. To increase the number of thermotolerant microbial biocatalysts that produce D‐LA, a derivative of <I>Bacillus subtilis</I> strain 168 that grows at 50°C was metabolically engineered. Since <I>B. subtilis</I> lacks a gene encoding D‐lactate dehydrogenase (<I>ldhA</I>), five heterologous <I>ldhA</I> genes (<I>B. coagulans ldhA</I> and <I>gldA101</I>, and <I>ldhA</I> from three <I>Lactobacillus delbrueckii</I>) were evaluated. Corresponding D‐LDHs were purified and biochemically characterized. Among these, D‐LDH from <I>L. delbrueckii</I> subspecies <I>bulgaricus</I> supported the highest D‐LA titer (about 1M) and productivity (2 g h<SUP>−1</SUP> g cells<SUP>−1</SUP>) at 37°C (<I>B. subtilis</I> strain DA12). The D‐LA titer at 48°C was about 0.6 M at a yield of 0.99 (g D‐LA g<SUP>−1</SUP>glucose consumed). Strain DA12 also fermented glucose at 48°C in mineral salts medium to lactate at a yield of 0.89 g g<SUP>−1</SUP> glucose and the D‐lactate titer was 180 ± 4.5 mM. These results demonstrate the potential of <I>B. subtilis</I> as a platform organism for metabolic engineering for production of chemicals at 48°C that could minimize process cost.</P>