Optimization of Carbon Dioxide and Valeric Acid Utilization for Polyhydroxyalkanoates Synthesis by Cupriavidus necator

Abstract

The utilization of captured CO2 as a part of the CO2 capture and storage system to produce biopolymers could address current environmental issues such as global warming and depletion of resources. In this study, the effect of feeding strategies of CO2 and valeric acid on cell growth and synthesis of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) [P(3HB-co-3HV)] in Cupriavidus necator was investigated to determine the optimal conditions for microbial growth and biopolymer accumulation. Among the studied CO2 concentrations (1-20 %), microbial growth and poly(3-hydroxybutyrate) accumulation were optimal at 1 % CO2 using a gas mixture at H-2:O-2:N-2 = 7:1:91 % (v/v). When valeric acid was fed together with 1 % CO2, (R)-3-hydroxyvalerate synthesis increased with increasing valeric acid concentration up to 0.1 %, but (R)-3-hydroxybutyrate synthesis was inhibited at > 0.05 % valeric acid. Sequential addition of valeric acid (0.05 % at Day 0 followed by 0.025 % at Day 2) showed an increase in 3HV fraction without inhibitory effects on 3HB synthesis during 4 d accumulation period. The resulting P(3HB-co-3HV) with 17-32 mol % of 3HV is likely to be biocompatible. The optimal concentrations and feeding strategies of CO2 and valeric acid determined in this study for microbial P(3HB-co-3HV) synthesis can be used to produce biocompatible P(3HB-co-3HV).