Synthesis of Carotenoids of Industrial Interest in the Photosynthetic Bacterium Rhodopseudomonas palustris : Bioengineering and Growth Conditions

Culture optimization to enhance carotenoid production of a selected purple nonsulfur bacterium and its activity against acute hepatopancreatic necrosis disease-causing Vibrio parahaemolyticus

Purple nonsulfur bacteria (PNSB) were investigated for their carotenoid production and anti-vibrio activity against acute hepatopancreatic necrosis disease (AHPND)-causing Vibrio parahaemolyticus. To test carotenoid production, selected strains were cultivated in basic isolation medium (BIM), glutamate acetate medium, G5 medium and artificial acetic acid wastewater (AAW) medium. From 144 PNSB, Rhodopseudomonas palustris KTSSG46 was selected to produce carotenoids under microaerobic light conditions in BIM. When the culture medium was optimized, strain KTSSG46 grown in BIM modified with l-glutamate at 1 g/L more effectively inhibited AHPND-causing V. parahaemolyticus strains than standard BIM with 1 g/L (NH₄ )₂ SO₄ . BIM was further modified with 1.23 g/L MgSO₄ ·7H₂ O and carotenoid production increased 40.22%. Carotenoid production at day 2 by strain KTSSG46 grown in BIM modified with l-glutamate at 1 and 1.23 g/L MgSO₄ ·7H₂ O was the same as production in BIM modified with monosodium glutamate (MSG). Culture supernatants from all BIM formulations showed similar activity against the resistant AHPND strain SR2. Based on high-performance liquid chromatography, carotenoids of strain KTSSG46 might be canthaxanthin. Grown in BIM modified with MSG, strain KTSSG46 could produce inexpensive carotenoids and release anti-vibrio compounds that, applied as shrimp feed additive, would prevent AHPND strains.

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.

Expression of Alternative Nitrogenases in Rhodopseudomonas palustris Is Enhanced Using an Optimized Genetic Toolset for Rapid, Markerless Modifications

The phototrophic bacterium Rhodopseudomonas palustris is emerging as a promising biotechnological chassis organism, due to its resilience to a range of harsh conditions, a wide metabolic repertoire, and the ability to quickly regenerate ATP using light. However, realization of this promise is impeded by a lack of efficient, rapid methods for genetic modification. Here, we present optimized tools for generating chromosomal insertions and deletions employing electroporation as a means of transformation. Generation of markerless strains can be completed in 12 days, approximately half the time for previous conjugation-based methods. This system was used for overexpression of alternative nitrogenase isozymes with the aim of improving biohydrogen productivity. Insertion of the pucBa promoter upstream of vnf and anf nitrogenase operons drove robust overexpression up to 4000-fold higher than wild-type. Transcript quantification was facilitated by an optimized high-quality RNA extraction protocol employing lysis using detergent and heat. Overexpression resulted in increased nitrogenase protein levels, extending to superior hydrogen productivity in bioreactor studies under nongrowing conditions, where promoter-modified strains better utilized the favorable energy state created by reduced competition from cell division. Robust heterologous expression driven by the pucBa promoter is thus attractive for energy-intensive biosyntheses suited to the capabilities of R. palustris. Development of this genetic modification toolset will accelerate the advancement of R. palustris as a biotechnological chassis organism, and insights into the effects of nitrogenase overexpression will guide future efforts in engineering strains for improved hydrogen production.

Eszett (ẞ; ß)-carotene is an erroneous, non-existent false positive of beta (β)-carotene

There are several isomers of carotene, the main ones being alpha and beta carotene (i.e., α-carotene and β-carotene). The latter serves as a precursor for vitamin A, and is thus a well-studied carotenoid in health, food, and nutrition research. A German special character, the Eszett (uppercase or capital ẞ; lowercase ß), has been confused with the Greek, lowercase beta (β) in some papers in the biomedical literature, and when the lowercase Eszett is written in italics, it looks even more similar to the Greek letter beta. Curiously, this linguistic error has given rise to a "new" form of carotene, Eszett (ß)-carotene, which does not exist. A search on PubMed, Elsevier's sciencedirect.com, and Springer Nature's SpringerLink platforms reveals that there are potentially dozens, if not hundreds of cases or more of this false-positive carotene "isomer," which was supposed to represent β-carotene, but has, through a typographic error, represented a "new" and non-existent form of carotene, ß-carotene. This clearly represents erroneous literature that needs correction.

Natural Pigments of Bacterial Origin and Their Possible Biomedical Applications

Microorganisms are considered one of the most promising niches for prospecting, production, and application of bioactive compounds of biotechnological interest. Among them, bacteria offer certain distinctive advantages due to their short life cycle, their low sensitivity to seasonal and climatic changes, their easy scaling as well as their ability to produce pigments of various colors and shades. Natural pigments have attracted the attention of industry due to an increasing interest in the generation of new products harmless to humans and nature. This is because pigments of artificial origin used in industry can have various deleterious effects. On this basis, bacterial pigments promise to be an attractive niche of new biotechnological applications, from functional food production to the generation of new drugs and biomedical therapies. This review endeavors to establish the beneficial properties of several relevant pigments of bacterial origin and their relation to applications in the biomedical area.

Engineering Photosynthetic Bioprocesses for Sustainable Chemical Production: A Review

Microbial production of chemicals using renewable feedstocks such as glucose has emerged as a green alternative to conventional chemical production processes that rely primarily on petroleum-based feedstocks. The carbon footprint of such processes can further be reduced by using engineered cells that harness solar energy to consume feedstocks traditionally considered to be wastes as their carbon sources. Photosynthetic bacteria utilize sophisticated photosystems to capture the energy from photons to generate reduction potential with such rapidity and abundance that cells often cannot use it fast enough and much of it is lost as heat and light. Engineering photosynthetic organisms could enable us to take advantage of this energy surplus by redirecting it toward the synthesis of commercially important products such as biofuels, bioplastics, commodity chemicals, and terpenoids. In this work, we review photosynthetic pathways in aerobic and anaerobic bacteria to better understand how these organisms have naturally evolved to harness solar energy. We also discuss more recent attempts at engineering both the photosystems and downstream reactions that transfer reducing power to improve target chemical production. Further, we discuss different methods for the optimization of photosynthetic bioprocess including the immobilization of cells and the optimization of light delivery. We anticipate this review will serve as an important resource for future efforts to engineer and harness photosynthetic bacteria for chemical production.

An overview of anoxygenic phototrophic bacteria and their applications in environmental biotechnology for sustainable Resource recovery

Anoxygenic phototrophic bacteria (APB) are a phylogenetically diverse group of organisms that can harness solar energy for their growth and metabolism. These bacteria vary broadly in terms of their metabolism as well as the composition of their photosynthetic apparatus. Unlike oxygenic phototrophic bacteria such as algae and cyanobacteria, APB can use both organic and inorganic electron donors for light-dependent fixation of carbon dioxide without generating oxygen. Their versatile metabolism, ability to adapt in extreme conditions, low maintenance cost and high biomass yield make APB ideal for wastewater treatment, resource recovery and in the production of high value substances. This review highlights the advantages of APB over algae and cyanobacteria, and their applications in photo-bioelectrochemical systems, production of poly-β-hydroxyalkanoates, single-cell protein, biofertilizers and pigments. The ecology of ABP, their distinguishing factors, various physiochemical parameters governing the production of high-value substances and future directions of APB utilization are also discussed.

Metabolic Engineering of Different Microbial Hosts for Lycopene Production

As a result of the extensive use of lycopene in a variety of fields, especially the dietary supplement and health food industries, the production of lycopene has attracted considerable interest. Lycopene can be obtained through extraction from vegetables and chemical synthesis. Alternatively, the microbial production of lycopene has been extensively researched in recent years. Various types of microbial hosts have been evaluated for their potential to accumulate a high level of lycopene. Metabolic engineering of the hosts and optimization of culture conditions are performed to enhance lycopene production. After years of research, great progress has been made in lycopene production. In this review, strategies used to improve lycopene production in different microbial hosts and the advantages and disadvantages of each microbial host are summarized. In addition, future perspectives of lycopene production in different microbial hosts are discussed.