Carbon preference by Cupriavidus necator for growth and accumulation phases: Heterotrophic vs. autotrophic metabolisms

Abstract

Cupriavidus necator is a mixotrophic microbe capable of metabolizing both organic carbon (heterotrophic) and CO 2 (autotrophic) for cell growth and biodegradable plastic synthesis. This study investigates C. necator's behavior under mixotrophic conditions for cell growth and polyhydroxyalkanoate (PHA) accumulation. Various concentrations of organic substrates (acetate and butyrate from 10 to 1000 mg/L) and gaseous substrates (H 2 , O 2 , CO 2 ) were examined to monitor C. necator's substrate preferences. The results indicated a clear preference for organic carbon over CO 2 during cell growth. At relatively low organic concentrations (10–100 mg/L), gas utilization began after complete consumption of organic substrates. On the other hand, higher concentrations (500–1000 mg/L) led to a shift from the heterotrophic to mixotrophic metabolism around the 10-h mark due to the abundance of substrates. During PHA accumulation, C. necator initially favored the gaseous substrates (H 2 and CO 2 ) before shifting to the organic substrates, with mixotrophic behavior observed immediately at low organic concentrations. Additionally, high CO 2 partial pressure (>0.4 atm) inhibited microbial growth in both autotrophic and heterotrophic metabolisms. These findings highlight C. necator's adaptability under mixotrophic conditions and demonstrate the potential for mass-scale applications, such as microbial electrolysis cells to optimize biopolymer production and substrate utilization. • C. necator's substrate preference was explored under mixotrophic conditions. • C. necator prefers organic substrates for growth but CO₂/H₂ for PHA accumulation. • High CO₂ levels inhibited growth, impacting metabolic efficiency. • Bacteria shifted between metabolism types based on initial substrate concentration. • PHA production by C. necator using MECs is highly feasible.

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