초록
<P><B>Abstract</B></P><P><B>BACKGROUND</B></P><P><I>Bacillus methylotrophicus</I> SK19.001 is a glutamate‐independent strain that produces poly(<I>γ</I>‐glutamic acid) (<I>γ</I>‐PGA), a polymer of <SMALL>d</SMALL>‐ and <SMALL>l</SMALL>‐glutamic acids that possesses applications in food, the environment, agriculture, etc. This study was undertaken to explore the synthetic pathway of intracellular <SMALL>l</SMALL>‐ and <SMALL>d</SMALL>‐glutamic acid in SK19.001 by investigating the effects of tricarboxylic acid cycle intermediates and different amino acids as metabolic precursors on the production of <I>γ</I>‐PGA and analyzing the activities of the enzymes involved in the synthesis of <SMALL>l</SMALL>‐ and <SMALL>d</SMALL>‐glutamate.</P><P><B>RESULTS</B></P><P>Tricarboxylic acid cycle intermediates and amino acids could participate in the synthesis of <I>γ</I>‐PGA via independent pathways in SK19.001. <SMALL>l</SMALL>‐Aspartate aminotransferase, <SMALL>l</SMALL>‐glutaminase and <SMALL>l</SMALL>‐glutamate synthase were the enzymatic sources of <SMALL>l</SMALL>‐glutamate. Glutamate racemase was responsible for the formation of <SMALL>d</SMALL>‐glutamate for the synthesis of <I>γ</I>‐PGA, and the synthetase had stereoselectivity for glutamate substrate.</P><P><B>CONCLUSION</B></P><P>The enzymatic sources of <SMALL>l</SMALL>‐glutamate were investigated for the first time in the glutamate‐independent <I>γ</I>‐PGA‐producing strain, and multiple enzymatic sources of <SMALL>l</SMALL>‐glutamate were verified in SK19.001, which will benefit efforts to improve production of <I>γ</I>‐PGA with metabolic engineering strategies. © 2015 Society of Chemical Industry</P>