The transition of Rhodobacter sphaeroides into a microbial cell factory.

Microbial cell factories are the workhorses of industrial biotechnology and improving their performances can significantly optimize industrial bioprocesses. Microbial strain engineering is often employed for increasing the competitiveness of bio-based product synthesis over more classical petroleum-based synthesis. Recently, efforts for strain optimization have been standardized within the iterative concept of "design-build-test-learn" (DBTL). This approach has been successfully employed for the improvement of traditional cell factories like Escherichia coli and Saccharomyces cerevisiae. Within the past decade, several new-to-industry microorganisms have been investigated as novel cell factories, including the versatile α-proteobacterium Rhodobacter sphaeroides. Despite its history as a laboratory strain for fundamental studies, there is a growing interest in this bacterium for its ability to synthesize relevant compounds for the bioeconomy, such as isoprenoids, poly-β-hydroxybutyrate, and hydrogen. In this study, we reflect on the reasons for establishing R. sphaeroides as a cell factory from the perspective of the DBTL concept. Moreover, we discuss current and future opportunities for extending the use of this microorganism for the bio-based economy. We believe that applying the DBTL pipeline for R. sphaeroides will further strengthen its relevance as a microbial cell factory. Moreover, the proposed use of strain engineering via the DBTL approach may be extended to other microorganisms that have not been critically investigated yet for industrial applications.