Journal of Bioremediation & Biodegradation
Open Access

Abstract

Poly((R)-3-hydroxybutyrate-co-(R)-3-hydroxyhexanoate) [P(3HB-co-3HHx)], a flexible and practical biodegradable plastic, is generally produced from plant oils and fatty acids by several wild and recombinant bacteria. Fukui and his coworkers constructed many recombinants of Ralstonia eutropha for studying biosynthesis of [P(3HB-co-3HHx)] with high 3HHx composition from the structurally unrelated carbon source. The engineered strain with ��phaB1 genotype expressing ccr, phaJ4a, and emd (R. eutropha strain MF01��B1/pBPP-ccrMeJ4a-emd) produced P (3HB-co-3HHx) composed of 22 mol% 3HHx at high cellular content from fructose (Metabolic Engineering, 27:38�45, 2015). Such high C6�monomer composition was achieved by improving artificial pathway for biosynthesis of monomer unit as follows: (i) Depression of (R)-specific reduction of acetoacetyl-CoA by the deletion of phaB1 for formation of the C6�monomer unit from fructose driven by crotonyl-CoA carboxylase/reductase (Ccr), (ii) co-overexpression of phaJ4a, which encodes medium-chain-length (R)-enoyl- CoA hydratase, with ccr promoted the incorporation of both 3HB and 3HHx units (iii) introduction of emdMm,a synthetic gene encoding ethylmalonyl-CoA decarboxylase derived from mouse which is probably converting ethylmalonyl-CoA generated by the reductive carboxylase activity of Ccr back into butyryl-CoA. R. eutropha is a facultative hydrogen-oxidizing bacterium that chemolithoautotrophically grows due to carbon dioxide fixation using H2 and O2 as the energy source. Hence, we also investigated the production of P(3HB-co-3HHx) from CO2 by the engineered strains of R. eutropha in chemolithoautotrophic condition using the substrate gas mixture (H2/O2/CO2::8:1:1) and mineral salts medium. As a result, the strain MF01��B1/ pBPP-ccrMeJ4a-emd produced P(3HB-co-3HHx) with a remarkably high composition of 3HHx (51.7 mol%) at a high cellular content (65.1 wt%) from CO2.

Biography

Kenji Tanaka has completed his PhD from Kyushu University. He is a Professor of Depatment of Biological and Environmental Chemistry, School of Humanity- Oriented Science & Engineering, Kindai University. His research field is Bioprocess Engineering. He has published many papers on microbial production of biodegradable plastic from CO2 and biomass.

Email: tanaka@fuk.kindai.ac.jp