Engineering Photosynthetic α-Proteobacteria for the Production of Recombinant Proteins and Terpenoids

Abstract

Phototrophic non-sulfur purple α-proteobacteria are able to harvest sunlight and to fix atmospheric carbon dioxide and dinitrogen. Consequently, these microbes are used as model organisms for the investigation of regulation and activity of the photosynthesis complexes, the ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBisCO) as well as the nitrogenase and hydrogenase enzyme complexes. In addition, this group of prokaryotic phototrophs has emerged as microbial production chassis for the synthesis of recombinant proteins and natural products. To this end, a versatile set of different expression tools has been developed allowing the functional expression of single genes as well as the transfer of complete metabolic pathways. This review provides an overview of different strategies to engineer photosynthetic α-proteobacteria, especially the two most commonly employed representatives Rhodobacter capsulatus and Rhodobacter sphaeroides, for the production of difficult-to-express proteins and terpenoids. Unique physiological properties of these alternative production hosts are discussed in the context of respective production processes. Furthermore, synthetic biology tools applicable for heterologous gene expression and establishment of combinatorial biosynthetic pathways in phototrophic α-proteobacteria are described. Finally, the potential of phototrophic bacteria in future bioeconomic production routes is briefly discussed.