Production of polyhydroxyalkanoates by<i>Azotobacter vinelandii</i>UWD in beet molasses culture

Abstract

Beet molasses (BM) has proven to be an excellent feedstock for polyhydroxyalkanoate (PHA) production by Azotobacter vinelandii UWD. The substrate-cost for PHA production from BM in fed-batch culture was one-third of that using glucose. Copolymers containing β-hydroxyvalerate are readily formed in BM medium when valerate is used as a precursor. The origin of the hydroxyvalerate monomer was most likely a β-ketoacyl-CoA intermediate in the β-oxidation of the odd-length n-alkanoates. BM also contained unidentified factors that stimulated PHA production to a greater extent than cell growth. Analysis of BM fractions has suggested that amino-N compounds may be required for PHA-yield-promotion. Thus the addition of a small amount of commercial peptone to mineral salts medium containing pure or other impure sugar sources has led to significantly increased PHA yields.