The gene dosage effect of carbonic anhydrase on the biosynthesis of poly(3-hydroxybutyrate) under autotrophic and mixotrophic culture conditions

Ralstonia eutropha is a hydrogen-oxidizing chemolithotrophic bacterium that can synthesize poly[( R )-3-hydroxybutyrate] [P(3HB)], which is used as a biodegradable plastic. Various genes coding for carbonic anhydrase (CA), which are involved in CO 2 fixation and metabolism, are present in the genome of R. eutropha . Although the significance of CA for CO 2 metabolism in R. eutropha is well known, CAs have never been deliberately employed to enhance P(3HB) production from CO 2 . Thus, we investigated the gene dosage effect of the β-carbonic anhydrase ( can ) gene on P(3HB) accumulation in R. eutropha H16 under autotrophic and mixotrophic conditions. The multicopy plasmid-based dosage of the can gene showed a 1.5-fold increase in P(3HB) content in cells grown under nitrogen-source-limited autotrophic conditions. A similar result was observed under nitrogen-source-limited mixotrophic conditions in the presence of glycerol. Thus, these findings suggest a viable strategy to increase P(3HB) yield under autotrophic and mixotrophic culture conditions.