The production of polyhydroxybutyrate by Methylobacterium rhodesianum and Ralstonia eutropha in media containing glycerol and casein hydrolysates

Methylobacterium rhodesianum and Ralstonia eutropha were cultivated to produce polyhydroxybutyrate (PHB) using media which contained glycerol and casein hydrolysates as C/N-substrates. In these media the pH had not to be regulated during the fermentations. The first strain accumulated an average of 39% PHB during 92 h of cultivation in flasks and 50% PHB during 45 h of cultivation in fermenters. The second one yielded an average of 47% PHB during 67 h of cultivation using casein peptone and 65% PHB during 45 h of cultivation using Casamino acids in the medium. Calculated N-balances showed that about 65% of the supplied nitrogen was used for growth of non-PHB cell dry mass. The conversion of glycerol to PHB was 17% (w/w).