Influence of the operon structure on poly(3-hydroxypropionate) synthesis in Shimwellia blattae

Glycerol has become a cheap and abundant carbon source due to biodiesel production at a large scale, and it is available for several biotechnological applications. We recently established poly(3-hydroxypropionate) [poly(3HP)] synthesis in a recombinant Shimwellia blattae strain (Heinrich et al. Appl Environ Microbiol 79:3582-3589, 2013). The major drawbacks of the current strains are (i) low poly(3HP) yields, (ii) low plasmid stability and (iii) insufficient conversion rates. In this study, we demonstrated the influence of alterations of the operon structure, consisting of 1,3-propanediol dehydrogenase (dhaT) and aldehyde dehydrogenase (aldD) of Pseudomonas putida KT2442, propionate:coenzyme A (propionate-CoA) transferase (pct) of Clostridium propionicum X2 and polyhydroxyalkanoate (PHA) synthase (phaC1) of Ralstonia eutropha H16. It was shown that S. blattae ATCC33430/pBBR1MCS-2::dhaT::pct::aldD::phaC1 synthesized up to 14.5 % (wtPHA/wtCDW) in a 2-L fed-batch fermentation process. Furthermore, we overcame the problem of plasmid losses during the fermentation period by engineering a carbon source-dependent plasmid addiction system in a triose phosphate isomerase knockout mutant. An assumed poly(3-hydroxyalkanoic acid) degrading activity of the lipase/esterase YbfF could not be confirmed.