Optimization of culture conditions for enhanced asymmetric bioreduction of acetophenone and its derivatives by growing cells of Pseudomonas sp. AP1

The microbial diversity of samples collected from a municipal solid waste disposal site located on outskirts of Amritsar (Punjab), India was isolated and screened for asymmetric transformation of acetophenone and its different derivatives to generate chiral synthons for commercially important drugs. A potential bacterial isolate AP1, identified as Pseudomonas sp., was selected for further studies as it transformed 1.0 g/L acetophenone to (R)-1-phenylethanol with an overall yield of 30.0% and enantiomeric excess (ee) ≤86% after 240 h. The activation of cells in the presence of acetophenone (2 mM) and optimization of nutrient supplements to minimal synthetic medium (MSM) significantly improved the transformation efficiency, as under optimized conditions cells of AP1 were able to transform 2.5 g/L acetophenone with an overall yield of 86% (ee≥96%, R) in just 54 h. The overall yield of (R)-1-phenylethanol was dependent on available mannitol at the time of addition of acetophenone (2.5 g/L) to growing cells. The oxidation of mannitol to fructose by NADPH dependent mannitol dehydrogenase assured continuous supply of reduced cofactor to support the transformation. The cells of AP1 also transformed different halo, hydroxy and amino derivatives of acetophenone with an overall yield of 41.0-78.0% and ee ≥95%.