Reductive capabilities of different cyanobacterial strains towards acetophenone as a model substrate - Prospect of applications for chiral building blocks synthesis

Bioreductive capabilities of four morphologically different strains of cyanobacteria have been assessed in this work. Arthrospira maxima, Leptolyngbya foveolarum, Nodularia sphaerocarpa and Synechococcus bigranulatus were applied as catalysts for the reduction of acetophenone to the corresponding chiral phenylethyl alcohol. The process was modified regarding substrate concentration, duration of pre-cultivation period, duration of biotransformation, LIGHT regime and glucose addition to the culture media. Obtained results clearly showed that cyanobacteria were active towards acetophenone what resulted in the substrate reduction to (S)-1-phenylethanol with high enantiomeric excess. The reaction efficiency increased with the biotransformation time, but the higher concentration of substrate limited the process yield. Also, all tested strains performed reaction with the highest efficacy under continuous LIGHT regime. The most active strains - N. sphaerocarpa and S. bigranulatus carried out the conversion of 1 mM acetophenone with high efficiency of respectively 97.6% and 96.2% after 13 days of biotransformation. A. maxima reached 45.8% of conversion after 13 days of biotransformation whereas L. foveolarum did not exceed 20%. The enantiomeric excesses were respectively 98.8%- A. maxima, 91.7%- L. foveolarum, 72.6%- S. bigranulatus and N. sphaerocarpa 16.2%.