Hydrogen production by Rhodobacter sphaeroides DSM 158 under intense irradiation

Engineering the Methylerythritol Phosphate Pathway and Using a Temporal Promoter for Enhanced Lycopene Production in Rhodobacter sphaeroides HY01

Rhodobacter sphaeroides HY01 is a high-yield strain for industrial production of coenzyme Q10 (Q10), indicating its potential for producing other terpenoids. However, the production of Q10 substantially depletes isoprene precursors, nearly eliminating other terpenoids like spheroidene and spheroidenone commonly found in wild-type R. sphaeroides. Lycopene was used as an example to demonstrate its potential for terpenoid biosynthesis. By refactoring the methylerythritol phosphate (MEP) pathway, such as overexpressing crtE and introducing crtI4, lycopene production reached 126.1 mg/L in HY01. However, further overexpression of the deoxy-d-xylulose-5-phosphate synthase, 1-deoxy-d-xylulose 5-phosphate reductoisomerase, and isopentenyl-diphosphate isomerase genes led to strain degradation, significantly reducing lycopene production. Fine-tuning the engineered PrrAB two-component system, which upregulated the MEP pathway, increased lycopene production to 154.9 mg/L. Inspired by this result, a series of native promoters with varying strengths were identified and characterized through transcriptomic analysis during the late fermentation stage. Using these temporal promoters to control genes in the MEP pathway ultimately increased lycopene production to 283.1 mg/L, the highest reported in R. sphaeroides. These results underscore the potential of HY01 as a chassis for terpenoid biosynthesis.

Sequential Dark-Photo Batch Fermentation and Kinetic Modelling for Biohydrogen Production Using Cheese Whey as a Feedstock

The present work describes the utilisation of cheese whey to produce biohydrogen by sequential dark-photo fermentation. In first stage, cheese whey was fermented by Enterobacter aerogenes 2822 cells in a 2 L double-walled cylindrical bioreactor to produce hydrogen/organic acids giving maximum biohydrogen yield and cumulative hydrogen of 2.43 ± 0.12 mol mol^-1 lactose and 3270 ± 143.5 mL at cheese whey concentration of 105 mM lactose L^-1. The soluble metabolites of dark fermentation when utilised as carbon source for photo fermentation by Rhodobacter sphaeroides O.U.001, the yield, and cumulative hydrogen was increased to 4.22 ± 0.20 mol mol^-1 VFA and 3800 ± 170 mL, respectively. Meanwhile, an overall COD removal of about 38.08% was also achieved. The overall biohydrogen yield was increased from 2.43 (dark fermentation) to 6.65 ± 0.25 mol mol^-1 lactose. Similarly, the modelling for biohydrogen production in bioreactor was done using modified Gompertz equation and Leudeking-Piret model, which gave adequate simulated fitting with the experimental values. The carbon material balance showed that acetic acid, lactic acid, and CO₂ along with microbial biomass were the main by-products of dark fermentation and comprised more than 75% of carbon consumed.

Synthesis of ethyl acetate from glucose by Kluyveromyces marxianus, Cyberlindnera jadinii and Wickerhamomyces anomalus depending on the induction mode

Ethyl acetate is currently produced from fossil carbon resources. This ester could also be microbially synthesized from sugar-rich wastes of the food industry. Wild-type strains with GRAS status are preferred for such applications. Production of ethyl acetate by wild-type yeasts has been repeatedly reported, but comparative studies with several strains at various induction modes are largely missing. Here, synthesis of ethyl acetate by three yeasts with GRAS status, Kluyveromyces marxianus DSM 5422, Cyberlindnera jadinii DSM 2361 and Wickerhamomyces anomalus DSM 6766, was studied under identical and well-defined conditions in an aerated bioreactor, by inducing the ester synthesis via iron or oxygen limitation. Balancing the ester synthesis was based on measured concentrations of ethyl acetate in the exhaust gas, delivering masses of synthesized ester and synthesis rates in a high temporal resolution. All tested yeasts synthesized ethyl acetate under these conditions, but the intensity varied with the strain and induction mode. The highest yields were achieved under iron limitation with K. marxianus (0.182 g g-1) and under oxygen limitation with W. anomalus (0.053 g g-1). Iron limitation proved to be the better inducer for ester synthesis while oxygen limitation favored ethanol formation. K. marxianus DSM 5422 was the most potent producer of ethyl acetate exhibiting the highest biomass-specific synthesis rate of 0.5 g g-1h-1 under moderate iron limitation.

H2 production by photofermentation in an innovative plate-type photobioreactor with meandering channels

Hydrogen production by Rhodobacter capsulatus is an anaerobic, photobiological process requiring specific mixing conditions. In this study, an innovative design of a photobioreactor is proposed. The design is based on a plate-type photobioreactor with an interconnected meandering channel to allow culture mixing and H₂ degassing. The culture flow was characterized as a quasi-plug-flow with radial mixing caused by a turbulent-like regime achieved at a low Reynolds number. The dissipated volumetric power was decreased 10-fold while maintaining PBR performances (production and yields) when compared with a magnetically stirred tank reactor. To increase hydrogen production flow rate, several bacterial concentrations were tested by increasing the glutamate concentration using fed-batch cultures. The maximum hydrogen production flow rate (157.7 ± 9.3 ml H₂ /L/h) achieved is one of the highest values so far reported for H₂ production by R. capsulatus. These first results are encouraging for future scale-up of the plate-type reactor.

Draft Genome Assembly of Rhodobacter sphaeroides 2.4.1 Substrain H2 from Nanopore Data

Rhodobacter sphaeroides is a purple bacterium with complex genomic architecture. Here, a draft genome is reported for R. sphaeroides strain 2.4.1 substrain H2, which was generated exclusively from Nanopore sequencing data.

Rhodobacter sphaeroides is a purple bacterium with complex genomic architecture. Here, a draft genome is reported for R. sphaeroides strain 2.4.1 substrain H2, which was generated exclusively from Nanopore sequencing data.

Biological hydrogen production: molecular and electrolytic perspectives

Exploration of renewable energy sources is an imperative task in order to replace fossil fuels and to diminish atmospheric pollution. Hydrogen is considered one of the most promising fuels for the future and implores further investigation to find eco-friendly ways toward viable production. Expansive processes like electrolysis and fossil fuels are currently being used to produce hydrogen. Biological hydrogen production (BHP) displays recyclable and economical traits, and is thus imperative for hydrogen economy. Three basic modes of BHP were investigated, including bio photolysis, photo fermentation and dark fermentation. Photosynthetic microorganisms could readily serve as powerhouses to successively produce this type of energy. Cyanobacteria, blue green algae (bio photolysis) and some purple non-sulfur bacteria (Photo fermentation) utilize solar energy and produce hydrogen during their metabolic processes. Ionic species, including hydrogen (H⁺) and electrons (e^-) are combined into hydrogen gas (H₂), with the use of special enzymes called hydrogenases in the case of bio photolysis, and nitrogenases catalyze the formation of hydrogen in the case of photo fermentation. Nevertheless, oxygen sensitivity of these enzymes is a drawback for bio photolysis and photo fermentation, whereas, the amount of hydrogen per unit substrate produced appears insufficient for dark fermentation. This review focuses on innovative advances in the bioprocess research, genetic engineering and bioprocess technologies such as microbial fuel cell technology, in developing bio hydrogen production.

Modeling population dynamics in a microbial consortium under control of a synthetic pheromone-mediated communication system

Microbial consortia can be used to catalyze complex biotransformations. Tools to control the behavior of these consortia in a technical environment are currently lacking. In the present study, a synthetic biology approach was used to build a model consortium of two Saccharomyces cerevisiae strains where growth and expression of the fluorescent marker protein EGFP by the receiver strain is controlled by the concentration of α-factor pheromone, which is produced by the emitter strain. We have developed a quantitative experimental and theoretical framework to describe population dynamics in the model consortium. We measured biomass growth and metabolite production in controlled bioreactor experiments, and used flow cytometry to monitor changes of the subpopulations and protein expression under different cultivation conditions. This dataset was used to parameterize a segregated mathematical model, which took into account fundamental growth processes, pheromone-induced growth arrest and EGFP production, as well as pheromone desensitization after extended exposure. The model was able to predict the growth dynamics of single-strain cultures and the consortium quantitatively and provides a basis for using this approach in actual biotransformations.

Effect of substrate concentration on hydrogen production by photo-fermentation in the pilot-scale baffled bioreactor

Effect of substrate concentration on photo-fermentative hydrogen production was studied with a self-designed 4m³ pilot-scale baffled photo-fermentative hydrogen production reactor (BPHR). The relationships between parameters, such as hydrogen production rate (HPR, mol H₂/m³/d), hydrogen concentration, pH value, oxidation-reduction potential, biomass concentration (volatile suspended solids, VSS) and reducing sugar concentration, during the photo-fermentative hydrogen production process were investigated. The highest HPR of 202.64±8.83mol/m³/d was achieved in chamber #3 at a substrate concentration of 20g/L. Hydrogen contents were in the range of 42.19±0.94%-49.71±0.27%. HPR increased when organic loading rate was increased from 3.3 to 20g/L/d, then decreased when organic loading rate was further increased to 25g/L/d. A maximum HPR of 148.65±4.19mol/m³/d was obtained when organic loading rate was maintained at 20g/L/d during continuous bio-hydrogen production.

Photo-fermentative hydrogen production in a 4m3 baffled reactor: Effects of hydraulic retention time

A 4m³ pilot-scale baffled continuous-flow photoreactor with four sequential chambers (#1-#4) was established and tested to evaluate its photo-fermentative hydrogen production from wastewater that contains (10g/L glucose using a functional consortium at 30°C, under light with an intensity of 3000±200lux with a hydraulic retention time (HRT) of 24-72h. The hydrogen production rate and the broth characteristics varied significantly in the flow direction. The hydrogen production rate was highest in chamber #1, and lower in chambers #2-#4 at an HRT of 72h, while the peak production rate shifted to the latter chambers as the HRT was shortened. The overall H₂ production rate increased as HRT decreased, but was not consistent with the predictions that were based on the complete-mixing assumption.

Effect of adding brewery wastewater to pulp and paper mill effluent to enhance the photofermentation process: wastewater characteristics, biohydrogen production, overall performance, and kinetic modeling

Although a significant amount of brewery wastewater (BW) is generated during beer production, the nutrients in the BW could be reused as a potential bio-resource for biohydrogen production. Therefore, improvements in photofermentative biohydrogen production due to a combination of BW and pulp and paper mill effluent (PPME) as a mixed production medium were investigated comprehensively in this study. The experimental results showed that both the biohydrogen yield and the chemical oxygen demand removal were improved through the combination of BW and PPME. The best biohydrogen yield of 0.69 mol H₂/L medium was obtained using the combination of 10 % BW + 90 % PPME (10B90P), while the reuse of the wastewater alone (100 % BW and 100 % PPME) resulted in 42.3 and 44.0 % less biohydrogen yields than the highest yield, respectively. The greatest light efficiency was 1.97 % and was also achieved using the combination of both wastewaters at 10B90P. This study revealed the potential of reusing and combining two different effluents together, in which the combination of BW and PPME improved the nutrients and light penetration into the mixed production medium.

Disruption of lactate dehydrogenase and alcohol dehydrogenase for increased hydrogen production and its effect on metabolic flux in Enterobacter aerogenes

Hydrogen production by Enterobacter aerogenes from glucose was enhanced by deleting the targeted ldhA and adh genes responsible for two NADH-consuming pathways which consume most NADH generated from glycolysis. Compared with the wild-type, the hydrogen yield of IAM1183-ΔldhA increased 1.5 fold. Metabolic flux analysis showed both IAM1183-ΔldhA and IAM1183-Δadh exhibited significant changes in flux, including enhanced flux towards the hydrogen generation. The lactate production of IAM1183-ΔldhA significantly decreased by 91.42%, while the alcohol yield of IAM1183-Δadh decreased to 30%. The mutant IAM1183-ΔldhA with better hydrogen-producing performance was selected for further investigation in a 5-L fermentor. The hydrogen production of IAM1183-ΔldhA was 2.3 times higher than the wild-type. Further results from the fermentation process showed that the pH decreased to 5.39 levels, then gradually increased to 5.96, indicating that some acidic metabolites might be degraded or uptaken by cells.