초록
<P><B>Abstract</B></P><P>The chiral building block (<I>S</I>)‐3‐hydroxyisobutyric acid [(<I>S</I>)‐3‐HIBA] was produced either by conversion of isobutyric acid or directly from glucose utilizing cells of <I>Pseudomonas taiwanensis</I> VLB120 B83 T7 as catalysts. This strain carries a point mutation in the gene encoding 3‐hydroxyisobutyrate dehydrogenase (<I>mmsB</I>), leading to its inactivation. The maximal specific activity in resting‐cell biotransformations using isobutyric acid as substrate was 4.9±0.4 U g<SUB>cdw</SUB><SUP>−1</SUP>. Overexpression of the 2‐ketoisovalerate pathway genes <I>alsS, ilvC,</I> and <I>ilvD</I>, and the introduction of <I>kivd</I> encoding 2‐ketoacid decarboxylase resulted in the efficient fermentative synthesis of (<I>S</I>)‐3‐HIBA directly from glucose. Up to 22 mM (2.3 g <SMALL>L</SMALL><SUP>−1</SUP>) (<I>S</I>)‐3‐HIBA were produced at 3.7±0.3 U g<SUB>cdw</SUB><SUP>−1</SUP> in repeated batch experiments without observable product degradation. Utilizing a biofilm reactor it was possible to continuously produce up to 6 mM (0.63 g <SMALL>L</SMALL><SUP>−1</SUP>) of (<I>S</I>)‐3‐hydroxyisobutyric acid with a volumetric productivity of 1.32 mmol<SUB>(<I>S</I>)‐3‐HIBA</SUB> h<SUP>−1</SUP> <SMALL>L</SMALL><SUP>−1</SUP>. Overall, the conversion of isobutyric acid to (<I>S</I>)‐3‐HIBA was found to be the rate‐limiting step, leading to the accumulation of a mixture of (<I>S</I>)‐3‐hydroxyisobutyric acid and isobutyric acid. This study demonstrates for the first time the production of (<I>S</I>)‐3‐HIBA from renewable carbon in shake flasks and biofilm reactors and sets the stage for further optimizations towards the efficient production of 3‐HIBA and its derivatives in continuous fermentations.</P>