초록
<P><B>Abstract</B></P><P><B>BACKGROUND</B></P><P>The effects of alkaline stress on γ‐PGA biosynthesis and the mechanism involved have not been investigated in glutamate‐free medium.</P><P><B>RESULTS</B></P><P>Effects of alkaline pH stress on the yield and molecular weight of γ‐PGA were investigated in a 50 L bioreactor, and transcriptional levels of relevant genes were measured to explain the mechanism. After alkaline stress treatment, the maximum γ‐PGA yield reached 36.26 g L<SUP>−1</SUP>, increased by 79% compared with the control. The transcription levels of γ‐PGA synthetase genes <I>pgsB</I> and <I>pgsC</I>, as well as their closely related regulation factors <I>degU</I> and <I>swrA</I>, were improved 18.9‐fold, 31.2‐fold, 3.0‐fold and 6.3‐fold, respectively. Moreover, transcriptional analysis showed that alkaline stress enhanced the biosynthesis of γ‐PGA precursor (glutamic acid) and reduced the formation of byproducts (acetoin and 2,3‐butanediol), which contributed to the improved production of γ‐PGA. In addition, alkaline stress reduced the γ‐PGA molecular weight, which might be due to the enhanced expression of γ‐PGA hydrolase PgdS.</P><P><B>CONCLUSION</B></P><P>The alkaline stress‐mediated strategy was developed to regulate the yield and molecular weight of γ‐PGA in the glutamate‐free medium, and the mechanism involved was explained through transcriptional analysis. © 2015 Society of Chemical Industry</P>