Biosynthesis of cycloartenol by expression of plant and bacterial oxidosqualene cyclases in engineered Rhodobacter capsulatus

Light-mediated control of gene expression in the anoxygenic phototrophic bacterium Rhodobacter capsulatus using photocaged inducers

Photocaged inducer molecules, especially photocaged isopropyl-β-d-1-thiogalactopyranoside (cIPTG), are well-established optochemical tools for light-regulated gene expression and have been intensively applied in Escherichia coli and other bacteria including Corynebacterium glutamicum, Pseudomonas putida or Bacillus subtilis. In this study, we aimed to implement a light-mediated on-switch for target gene expression in the facultative anoxygenic phototroph Rhodobacter capsulatus by using different cIPTG variants under both phototrophic and non-phototrophic cultivation conditions. We could demonstrate that especially 6-nitropiperonyl-(NP)-cIPTG can be applied for light-mediated induction of target gene expression in this facultative phototrophic bacterium. Furthermore, we successfully applied the optochemical approach to induce the intrinsic carotenoid biosynthesis to showcase engineering of a cellular function. Photocaged IPTG thus represents a light-responsive tool, which offers various promising properties suitable for future applications in biology and biotechnology including automated multi-factorial control of cellular functions as well as optimization of production processes.

Engineering phototrophic bacteria for the production of terpenoids

With more than 80 000 compounds, terpenoids represent one of the largest classes of secondary metabolites naturally produced by various plants and other organisms. Owing to the tremendous structural diversity, they offer a wide range of properties relevant for biotechnological and pharmaceutical applications. In this context, heterologous terpenoid production in engineered microbial hosts represents an often cost-effective and eco-friendly way to make these valuable compounds industrially available. This review provides an overview of current strategies to employ and engineer oxygenic and anoxygenic phototrophic bacteria as alternative cell factories for sustainable terpenoid production. Besides terpenoid pathway engineering, the effects of different illumination strategies on terpenoid photoproduction are key elements in the latest studies.

Heterologous Production of Plant Terpenes in the Photosynthetic Bacterium Rhodobacter capsulatus

Terpenes are one of the largest classes of secondary metabolites that occur in all kingdoms of life and offer diverse valuable properties for food and pharma industry including pleasant odor or taste as well as antimicrobial or anticancer activities. A multitude of terpene biosynthesis pathways are known, but their efficient biotechnological exploitation requires an adequate microorganism as host which can ideally provide an optimal supply with biosynthetic isoprene precursors. Rhodobacter capsulatus, a Gram-negative, facultative anaerobic, photosynthetic non-sulfur purple bacterium belonging to the α-proteobacteria represents such a host particularly suitable for terpene production. Here, we describe methods for the expression of terpene biosynthetic enzymes in R. capsulatus and the extraction of products for analysis. At the same time, we summarize the current strategies to adjust the biosynthetic precursor supply via isoprenoid biosynthetic pathways.

A Direct Organocatalytic Enantioselective Route to Functionalized trans-Diels-Alder Products Having the Norcarane Scaffold

An enantioselective methodology to construct trans-Diels-Alder scaffolds by organocatalysis with excellent selectivity, high yield and up to five contiguous stereocenters is presented. The reaction concept integrates the halogen effect and a novel discovered pseudo-halogen effect to direct an endo-selective, secondary-amine catalyzed Diels-Alder reaction allowing for the subsequent formation of trans-Diels-Alder cycloadducts featuring the norcarene scaffold. The methodology relies on the reaction between an in situ generated trienamine and an α-brominated or α-pseudo-halogenated enone to form a fleeting cis-Diels-Alder intermediate. The endo-transition state-enhanced by the (pseudo-)halogen effect-sets the stereochemistry that allows for a subsequent S_N 2-like reaction at a tertiary center to obtain the trans-Diels-Alder scaffold. The mechanism was investigated and supported by experimental results as well as computational studies.