Inhibitory effect of medium-chain-length fatty acids on synthesis of polyhydroxyalkanoates from volatile fatty acids by Ralstonia eutropha

Medium-chain-length fatty acids, such as nonanoic (9:0) and octanoic (8:0) acids, are more toxic to Ralstonia eutropha than volatile fatty acids such as acetic, propionic and butyric acids. Nonanoic acid was degraded to aceti c and propionic acids via beta -oxidation by Ralstonia eutropha for cell gr owth and synthesis of polyhydroxyalkanoates (PHAs). In a mixture of the fat ty acids, utilization of nonanoic acid was depressed by acetic and propioni c acids, and vice versa. The PHA accumulation from the volatile fatty acids was decreased from 53% (w/w) of dry cell mass to 23% due to the nonanoic a cid. Similar phenomena were also observed with octanoic acid and its metabo lic intermediates, acetic and butyric acids.