Development of a closed-loop control system for production of medium-chain-length poly(3-hydroxyalkanoates) (mcl-PHAs) from bacteria

Abstract

Large scale availability of bacterial polyhydroxyalkanoates (PHAs) is still limited to a few types of short-chain-length PHAs, namely poly(3-hydroxybutyrate) (PHB) and its copolymer Biopol , consisting of 3-hydroxybutyrate and 3-hydroxyvalerate repeating units. In order to increase the number of available medium-chain-length PHA (mcl-PHA) copolymers a flexible high-cell-density fed-batch process was developed. Continuous process monitoring and substrate control were achieved by coupling on-line gaschromatography (on-line GC) to a software-based Proportional Integral (PI) substrate controller. System development time and continuous system upgrading were considerably shortened by using LABView , a powerful graphical programming environment. The control of octanoic acid and 10-undecenoic acid at 1.5 and 0.5 gL -1 respectively, enabled the production of high levels of biomass (30 gL -1 ) and mcl-PHA (10.5 gL -1 ) by avoiding substrate limitations or toxicities. The resulting mcl-PHA was an amorphous copolyester consisting of 37 mol% unsaturated monomers. The present system represents a valuable tool for the production of tailor-made mcl-PHAs, where the desired monomer composition is determined by the ratio of added cosubstrates.