Metabolic analysis on fatty acid utilization by Pseudomonas oleovorans: mcl-poly(3-hydroxyalkanoates) synthesis versus β-oxidation

Abstract

Medium chain length (mcl) polyhydroxyalkanoates (PHAs) are a type of natural elastomer with potential applications in tissue engineering and drug delivery. Pseudomonas oleovorans was cultivated in a 2 l fermenter for investigation of mcl-PHAs synthesis and β-oxidation of two mcl fatty acids, nonanoic acid (NA) and octanoic acid (OA), and the regulation role of acetic acid as a co-substrate. With a maximum PHA content around 34 wt.% of cell mass, the polyesters produced were co-polymers and the composition was dependent on both mcl-fatty acids and acetic acid. Acetic acid was the major extracellular metabolic intermediate by P. oleovorans on pure NA (or OA), released at high NA consumption rate (up to 1.9 mmol g −1 h −1), but taken up at low NA concentration levels. The specific NA consumption rate was a sum of specific PHA synthesis rate ( r PHA) and specific formation rate of valeryl-CoA ( r V-CoA) due to β-oxidation. The ratio of r PHA to r V-CoA was a good indicator of PHA synthesis efficiency on NA because valeryl-CoA was not incorporated into the polymer instead exclusively for energy supply and cell mass synthesis. This ratio could be improved by adding acetic acid as a co-substrate to the mcl fatty acids, and the yield of PHA on NA was increased from 0.24 to 0.33 g g −1. The polymer composition was also changed with more 3-hydroxynonanoate and less 3-hydroxyheptanonate in the copolymers because of the depressed β-oxidation in the presence of external acetic acid. Similar results were also obtained when P. oleovorans was fed with OA, an even-carbon-number fatty acid, with or without acetic acid as a co-substrate.