Isoprene production by Rhodobacter sphaeroides and its antimicrobial activity

Increase CO2 recycling of Escherichia coli containing CBB genes by enhancing solubility of multiple expressed proteins from an operon through temperature reduction

IMPORTANCE

In a previous study, we successfully engineered Escherichia coli capable of endogenous CO2 recycling through the heterologous expression of the Calvin-Benson Bassham genes. Establishing an efficient gene expression environment for recombinant strains is crucial, on par with the importance of metabolic engineering design. Therefore, the primary objective of this study was to further mitigate greenhouse gas emissions by investigating the effects of culture temperature on the formation of inclusion bodies (IB) and CO2 fixation activity in the engineered bacterial strain. The findings demonstrate that lowering the culture temperature effectively suppresses IB formation, enhances CO2 recycling, and concurrently increases the accumulation of organic acids. This temperature control approach, without adding or modifying compounds, is both convenient and efficient for enhancing CO2 recycling. As such, additional optimization of various environmental parameters holds promise for further enhancing the performance of recombinant strains efficiently.

Metabolic flux analysis of coenzyme Q10 synthesized by Rhodobacter sphaeroides under the influence of different pH regulators

Coenzyme Q10 (CoQ10) is crucial for human beings, especially in the fields of biology and medicine. The aim of this experiment was to investigate the conditions for increasing CoQ10 production. At present, microbial fermentation is the main production method of CoQ10, and the production process of microbial CoQ10 metabolism control fermentation is very critical. Metabolic flux is one of the most important determinants of cell physiology in metabolic engineering. Metabolic flux analysis (MFA) is used to estimate the intracellular flux in metabolic networks. In this experiment, Rhodobacter sphaeroides was used as the research object to analyze the effects of aqueous ammonia (NH3·H2O) and calcium carbonate (CaCO3) on the metabolic flux of CoQ10. When CaCO3 was used to adjust the pH, the yield of CoQ10 was 274.43 mg·L-1 (8.71 mg·g-1 DCW), which was higher than that of NH3·H2O adjustment. The results indicated that when CaCO3 was used to adjust pH, more glucose-6-phosphate (G6P) entered the pentose phosphate (HMP) pathway and produced more NADPH, which enhanced the synthesis of CoQ10. At the chorismic acid node, more metabolic fluxes were involved in the synthesis of p-hydroxybenzoic acid (pHBA; the synthetic precursor of CoQ10), enhancing the anabolic flow of CoQ10. In addition, Ca2+ produced by the reaction of CaCO3 with organic acids promotes the synthesis of CoQ10. In summary, the use of CaCO3 adjustment is more favorable for the synthesis of CoQ10 by R. sphaeroides than NH3·H2O adjustment. The migration of metabolic flux caused by the perturbation of culture conditions was analyzed to compare the changes in the distribution of intracellular metabolic fluxes for the synthesis of CoQ10. Thus, the main nodes of the metabolic network were identified as G6P and chorismic acid. This provides a theoretical basis for the modification of genes related to the CoQ10 synthesis pathway.

Evaluation of Growth and Utilization Potential of Rhodobacter sphaeroides in Reused Medium

Rhodobacter sphaeroides is a metabolically versatile purple non-sulfur bacteria that can produce valuable substances. As the low-cost and high-efficiency production of valuable substances is attracting attention, the reuse of the medium is emerging as a promising strategy. Therefore, in this study, the growth of R. sphaeroides was evaluated by reusing the medium of Escherichia coli and Saccharomyces cerevisiae. As a result, in the reuse of the medium in which S. cerevisiae was cultured, sufficient growth of R. sphaeroides could be confirmed, and especially, the growth of R. sphaeroides was not inhibited under aerobic conditions. Therefore, it is considered that the strategy of reusing the medium of S. cerevisiae is sufficiently feasible. Of the organic compounds investigated, R. sphaeroides grew best in succinic acid, followed by malic acid, citric acid, acetic acid, and glucose. In addition, by comparing photopigment synthesis in the reused medium, we propose the hypothesis that succinic acid may play an important role in photopigment synthesis for the first time.

Optimized Rhodobacter sphaeroides for the Production of Antioxidants and the Pigments with Antioxidant Activity

The photosynthetic bacterium, Rhodobacter sphaeroides, is a bacterium that can grow in a variety of environments and produces substances with antioxidant effects. In this study, we investigated the culture conditions to increase the production of antioxidants in R. sphaeroides, which can grow under both aerobic and anaerobic conditions. After incubation in the exponential phase and stationary phase under both conditions, a 2,2-diphenyl-1-picrylhydrazyl assay was used to confirm the antioxidant effect. Although the highest antioxidant effect was shown in the stationary phase under aerobic conditions, the antioxidant effect of each cell was found to be greater when cultured under anaerobic conditions. The antioxidant activity of R. sphaeroides was increased by sonication. In addition, the contents of carotenoids and bacteriochlorophyll, which are pigments with antioxidant effects, produced by R. sphaeroides were measured. We confirmed that the content of carotenoids was higher in anaerobic conditions than in aerobic conditions. However, when measuring the content of the bacterium, we found that there was more content in aerobic conditions. Therefore, we confirm that when grown in anaerobic conditions, the antioxidant effect of R. sphaeroides is higher, which suggests that this antioxidant effect comes from the effect of carotenoid.

Peering down the sink: A review of isoprene metabolism by bacteria

Isoprene (2-methyl-1,3-butadiene) is emitted to the atmosphere each year in sufficient quantities to rival methane (>500 Tg C yr^-1 ), primarily due to emission by trees and other plants. Chemical reactions of isoprene with other atmospheric compounds, such as hydroxyl radicals and inorganic nitrogen species (NO_x ), have implications for global warming and local air quality, respectively. For many years, it has been estimated that soil-dwelling bacteria consume a significant amount of isoprene (~20 Tg C yr^-1 ), but the mechanisms underlying the biological sink for isoprene have been poorly understood. Studies have indicated or confirmed the ability of diverse bacterial genera to degrade isoprene, whether by the canonical iso-type isoprene degradation pathway or through other less well-characterized mechanisms. Here, we review current knowledge of isoprene metabolism and highlight key areas for further research. In particular, examples of isoprene-degraders that do not utilize the isoprene monooxygenase have been identified in recent years. This has fascinating implications both for the mechanism of isoprene uptake by bacteria, and also for the ecology of isoprene-degraders in the environments.