Enhanced photo-fermentative hydrogen production by Rhodobacter capsulatus with pigment content manipulation

Impact of light spectra on photo-fermentative biohydrogen production by Rhodobacter sphaeroides KKU-PS1

Purple non-sulphur bacteria can only capture up to 10 % light spectra and only 1-5 % of light is converted efficiently for biohydrogen production. To enhance light capture and conversion efficiencies, it is necessary to understand the impact of various light spectra on light harvesting pigments. During photo-fermentation, Rhodobacter sphaeroides KKU-PS1 cultivated at 30 °C and 150 rpm under different light spectra has been investigated. Results revealed that red light is more beneficial for biomass accumulation, whereas green light showed the greatest impact on photo-fermentative biohydrogen production. Light conversion efficiency by green light is 2-folds of that under control white light, hence photo-hydrogen productivity is ranked as green > red > orange > violet > blue > yellow. These experimental data demonstrated that green and red lights are essential for photo-hydrogen and biomass productions of R. sphaeroides and a clearer understanding that possibly pave the way for further photosynthetic enhancement research.

Multidimensional optimization for accelerating light-powered biocatalysis in Rhodopseudomonas palustris

BACKGROUND

Whole-cell biocatalysis has been exploited to convert a variety of substrates into high-value bulk or chiral fine chemicals. However, the traditional whole-cell biocatalysis typically utilizes the heterotrophic microbes as the biocatalyst, which requires carbohydrates to power the cofactor (ATP, NAD (P)H) regeneration.

RESULTS

In this study, we sought to harness purple non-sulfur photosynthetic bacterium (PNSB) as the biocatalyst to achieve light-driven cofactor regeneration for cascade biocatalysis. We substantially improved the performance of Rhodopseudomonas palustris-based biocatalysis using a highly active and conditional expression system, blocking the side-reactions, controlling the feeding strategy, and attenuating the light shading effect. Under light-anaerobic conditions, we found that 50 mM ferulic acid could be completely converted to vanillyl alcohol using the recombinant strain with 100% efficiency, and > 99.9% conversion of 50 mM p-coumaric acid to p-hydroxybenzyl alcohol was similarly achieved. Moreover, we examined the isoprenol utilization pathway for pinene synthesis and 92% conversion of 30 mM isoprenol to pinene was obtained.

CONCLUSIONS

Taken together, these results suggested that R. palustris could be a promising host for light-powered biotransformation, which offers an efficient approach for synthesizing value-added chemicals in a green and sustainable manner.

Research and economic perspectives on an integrated biorefinery approach for the simultaneous production of polyhydroxyalkanoates and biohydrogen

Alarming environmental impacts have been resulted across the globe due to the recovery and consumption of fossil fuels. The elevated global carbon footprint has paved the way to an alternative to combat the prevalent pollution. On the other hand, the fossil-based plastics produced from the byproducts of petroleum remain intact in the environment leading to pollution. Fossil abated bioproducts are in high demand due to the increase in pollution. This call to utilize feedstock for simultaneous production of biologically useful products through carbon capture utilisation where the leftover carbon-rich substrate is converted into usable chemicals like bioplastics, methanol, urea and various other industrially essential components. The present review extensively focuses on the research and economic perspectives of an integrated biorefinery and addresses technical breaches, bottlenecks, and efficient strategies for the simultaneous production of biohydrogen and polyhydroxyalkanoates.

Enhancement strategies for photo-fermentative biohydrogen production: A review

Biohydrogen production by photo fermentation is an attractive clean energy production approach with less environmental pollution and higher substrate conversion. In recent years, various measures have been used to improve biohydrogen production performance, but there is a lack of systematic and comprehensive summary and analysis. Hence, the recent literatures on enhancing biohydrogen production by photo fermentation were summarized, and the functional mechanisms of enhancement strategies were explained. In this work, these measures were divided into four categories according to their roles in photo fermentation, including substrate pretreatment, bacterial modification and immobilization, additive addition, reactor design optimization. It can be concluded that the optimal enhancement conditions of each strategy were affected by substrate type, strain and process parameters. According to the results of this work, it was expected to give readers a clear understanding and provide a scientific reference of the research of photosynthetic biohydrogen production.

Enhancement of biohydrogen production rate in Rhodospirillum rubrum by a dynamic CO-feeding strategy using dark fermentation

BACKGROUND

Rhodospirillum rubrum is a purple non-sulphur bacterium that produces H₂ by photofermentation of several organic compounds or by water gas-shift reaction during CO fermentation. Successful strategies for both processes have been developed in light-dependent systems. This work explores a dark fermentation bioprocess for H₂ production from water using CO as the electron donor.

RESULTS

The study of the influence of the stirring and the initial CO partial pressure (p_CO) demonstrated that the process was inhibited at p_CO of 1.00 atm. Optimal p_CO value was established in 0.60 atm. CO dose adaptation to bacterial growth in fed-batch fermentations increased the global rate of H₂ production, yielding 27.2 mmol H₂ l^-1 h^-1 and reduced by 50% the operation time. A kinetic model was proposed to describe the evolution of the molecular species involved in gas and liquid phases in a wide range of p_CO conditions from 0.10 to 1.00 atm.

CONCLUSIONS

Dark fermentation in R. rubrum expands the ways to produce biohydrogen from CO. This work optimizes this bioprocess at lab-bioreactor scale studying the influence of the stirring speed, the initial CO partial pressure and the operation in batch and fed-batch regimes. Dynamic CO supply adapted to the biomass growth enhances the productivity reached in darkness by other strategies described in the literature, being similar to that obtained under light continuous syngas fermentations. The kinetic model proposed describes all the conditions tested.

Advances and bottlenecks in microbial hydrogen production

Biological production of hydrogen is poised to become a significant player in the future energy mix. This review highlights recent advances and bottlenecks in various approaches to biohydrogen processes, often in concert with management of organic wastes or waste CO₂. Some key bottlenecks are highlighted in terms of the overall energy balance of the process and highlighting the need for economic and environmental life cycle analyses with regard also to socio‐economic and geographical issues.

Screening and hydrogen-producing characters of a highly efficient H₂-producing mutant of Rhodovulum sulfidophilum P5

In this study, transposon mutagenesis technology was utilized to enhance the hydrogen production capability of a wild marine photosynthetic bacterium Rhodovulum sulfidophilum P5. A mutant strain TH-253 that exhibited high hydrogen yield and weaker light absorption ability was screened. Under strong light conditions, the mutant produced more hydrogen than that of the WT. Under optimum light intensity (120 μmol photons/m(2)s), the mutant achieved its highest hydrogen yield (1,436 ± 44 mL H2/L, about 3.21 ± 0.10 mol H2/mol acetate), which was 40.37% higher that of the WT. In continuous operation mode, the hydrogen yield (3.59 ± 0.11 mol H2/mol acetate) and average hydrogen production rate (16.91 ± 0.46 mL H2/Lh) of the mutant were 43.40% and 45.07% higher than those of the WT, respectively. The mutant strain TH-253 may be used as an appropriate starting strain for future photosynthesis-based large scale hydrogen production.