Hydrogen-oxidizing Bacterium Research Articles

Enrichment of hydrogen-oxidizing bacteria using a hybrid biological-inorganic system.

Hybrid biological-inorganic (HBI) systems comprising inorganic water-splitting catalysts and aerobic hydrogen-oxidizing bacteria (HOB) have previously been used for CO2 conversion. In order to identify new biocatalysts for CO2 conversion, the present study used an HBI system to enrich HOB directly from environmental samples. Three sediment samples (from a brackish water pond, a beach, and a tide pool) and two activated sludge samples (from two separate sewage plants) were inoculated into HBI systems using a cobalt phosphorus (Co-P) alloy and cobalt phosphate (CoPi) as inorganic catalysts with a fixed voltage of 2.0V. The gas composition of the reactor headspaces and electric current were monitored. An aliquot of the reactor medium was transferred to a new reactor when significant consumption of H2 and CO2 was detected. This process was repeated twice (with three reactors in operation for each sample) to enrich HOB. Increased biomass concomitant with increased H2 and CO2 consumption was observed in the third reactor, indicating enrichment of HOB. 16S rRNA gene amplicon sequencing demonstrated enrichment of sequences related to HOB (including bacteria from Mycobacterium, Hydrogenophaga, and Xanthobacter genera) over successive sub-cultures. Finally, four different HOB belonging to the Mycobacterium, Hydrogenophaga, Xanthobacter, and Acidovorax genera were isolated from reactor media, representing potential candidates as HBI system biocatalysts.

Bacterial Communities in a Gradient of Abiotic Factors Near a Sulfide Thermal Spring in Northern Baikal

The structure and diversity of microbial communities developing in the combined gradient of temperature (44–19 °C), as well as concentration of oxygen (0–10 mg/L) and hydrogen sulfide (33–0.7 mg/L), were studied in the thermal sulfide spring on the coast of Northern Lake Baikal. The predominance of bacteria participating in sulfur and nitrogen cycles and significant changes in the composition of microbial communities were noted at changing physicochemical conditions. Thiovirga sp. (sulfur-oxidizing bacteria, up to 37%) and Azonexus sp. (nitrogen-fixing bacteria, up to 43%) were dominant at high temperatures and concentrations of hydrogen sulfide in two hydrotherms. In addition, a significant contribution of the Rhodocyclaceae family (up to 51%) which is involved in the denitrification processes, and Acetoanaerobium sp. (up to 20%) fixing carbon oxide were found in the spring water. In the stream, mainly oxygenic cyanobacteria (up to 56%) developed at a temperature of 33 °C, in the presence of hydrogen sulfide and oxygen. In addition, sulfur bacteria of the genus Thiothrix (up to 48%) found in epibiotic communities of benthic animals of Lake Baikal were present here. Thiothrix sp. formed massive fouling in the zone of mixing lake and thermal waters with a significant contribution of hydrogen-oxidizing bacteria of the genus Hydrogenophaga (up to 22.5%). As well as chemolitho- and phototrophic bacteria, chemoorganotrophs (phyla Firmicutes, Chloroflexi, Desulfobacterota, Nitrospirota, Fibrobacterota, etc.) have been identified in all communities. The chemical parameters of water in spring and coastal zones indicate a significant change in the composition of thermal waters occurring with the participation of diverse microbial communities that contribute to the assimilation of inorganic components of mineral thermal waters.

Bacteria in the biosynthesis of animal nutrition components for crews of autonomous transport systems

The International Space Station (ISS) is currently using a water electrolysis process to produce oxygen. The hydrogen produced as a by-product is removed overboard. Carbon dioxide from crew breathing, dissolved in the atmosphere of the station, are extracted and also removed outside the station, but NASA expects to use it and convert it by the physicochemical reaction Sabatier in methane and water. Water will be used for crew needs and electrolysis, and methane is also planned to be removed overboard. When these interrelated processes work, very important substances are lost: methane, carbon dioxide, and hydrogen. This situation can be remedied by including in the life support system (LSS) of the ATS closed biotechnological regeneration cycles operating in a waste-free mode and synergistically solving the problems of complex provision of the crew with oxygen, water, and, most importantly, food. The process of biological oxidation of methane by methanotrophs bacteria is observed in nature in the first link of the food chain of the world's ocean and has long been used in terrestrial conditions for the industrial production of animal biomass for food and feed purposes. The same can be said about the use of hydrogen bacteria, which use carbon dioxide as a carbon source, with hydrogen as their energy source. Tolerance of these cultures to common nutrient media and the same technological parameters of biosynthesis allows their joint cultivation to obtain animal ingredients for crew food. The proposed work is devoted to the study of alternative processes, integrated use of carbon dioxide, methane, and hydrogen in LSS ATS.

Hydrogen Oxidizing Bacteria as Novel Protein Source for Human Consumption: An Overview

The increasing threat of climate change combined with the prospected growth in the world population puts an enormous pressure on the future demand for sustainable protein sources for human consumption. In this review, hydrogen oxidizing bacteria (HOB) are presented as a novel protein source that could play a role in fulfilling this future demand. HOB are species of bacteria that merely require an inflow of the gasses hydrogen, oxygen, carbon dioxide, and a nitrogen source to grow in a conventional bioreactor. Cupriavidus necator is proposed as HOB for industrial cultivation due to its remarkably high protein content (up to 70% of mass), suitability for cultivation in a bioreactor, and the vast amount of available background information. A broad overview of the unique aspects of the bacteria will be provided, from the production process, amino acid composition, and source of the required gasses to the future acceptance of HOB into the market.

Engineering Cupriavidus necator H16 for enhanced lithoautotrophic poly(3-hydroxybutyrate) production from CO2

BackgroundA representative hydrogen-oxidizing bacterium Cupriavidus necator H16 has attracted much attention as hosts to recycle carbon dioxide (CO2) into a biodegradable polymer, poly(R)-3-hydroxybutyrate (PHB). Although C. necator H16 has been used as a model PHB producer, the PHB production rate from CO2 is still too low for commercialization.ResultsHere, we engineer the carbon fixation metabolism to improve CO2 utilization and increase PHB production. We explore the possibilities to enhance the lithoautotrophic cell growth and PHB production by introducing additional copies of transcriptional regulators involved in Calvin Benson Bassham (CBB) cycle. Both cbbR and regA-overexpressing strains showed the positive phenotypes for 11% increased biomass accumulation and 28% increased PHB production. The transcriptional changes of key genes involved in CO2—fixing metabolism and PHB production were investigated.ConclusionsThe global transcriptional regulator RegA plays an important role in the regulation of carbon fixation and shows the possibility to improve autotrophic cell growth and PHB accumulation by increasing its expression level. This work represents another step forward in better understanding and improving the lithoautotrophic PHB production by C. necator H16.

Aerobic hydrogen-oxidizing bacteria in soil: from cells to ecosystems

Aerobic hydrogen-oxidizing bacteria in soil: from cells to ecosystems

Continuous Supply of Non-Combustible Gas Mixture for Safe Autotrophic Culture to Produce Polyhydroxyalkanoate by Hydrogen-Oxidizing Bacteria.

Polyhydroxyalkanoates (PHAs) are eco-friendly plastics that are thermoplastic and biodegradable in nature. The hydrogen-oxidizing bacterium Ralstonia eutropha can biosynthesize poly[(R)-3-hydroxybutyrate] [P(3HB)], the most common PHA, from carbon dioxide using hydrogen and oxygen as energy sources. In conventional autotrophic cultivation using R. eutropha, a gas mixture containing 75–80 vol% hydrogen is supplied; however, a gas mixture with such a high hydrogen content has a risk of explosion due to gas leakage. In this study, we aimed to develop an efficient cell culture system with a continuous supply of a non-combustible gas mixture (H2: O2: CO2: N2 = 3.8: 7.3: 13.0: 75.9) for safe autotrophic culture to produce P(3HB) by hydrogen-oxidizing bacteria, with a controlled hydrogen concentration under a lower explosive limit concentration. When the gas mixture was continuously supplied to the jar fermentor, the cell growth of R. eutropha H16 significantly improved compared to that in previous studies using flask cultures. Furthermore, an increased gas flow rate and agitation speed enhanced both cell growth and P(3HB) production. Nitrogen source deficiency promoted P(3HB) production, achieving up to 2.94 g/L P(3HB) and 89 wt% P(3HB) content in the cells after 144 h cultivation. R. eutropha NCIMB 11599, recombinant R. eutropha PHB-4, and Azohydromonas lata grew in a low-hydrogen-content gas mixture. R. eutropha H16 and recombinant R. eutropha PHB-4 expressing PHA synthase from Bacillus cereus YB-4 synthesized P(3HB) with a high weight-average molecular weight of 13.5–16.9 × 105. Thus, this autotrophic culture system is highly beneficial for PHA production from carbon dioxide using hydrogen-oxidizing bacteria as the risk of explosion is eliminated.

Coupled microscale zero valent iron-autotrophic hydrogen bacteria dechlorination system is not always superior to its standalone counterparts: A sustainable remediation perspective

The coupling of microscale zero-valent iron with autotrophic hydrogen bacteria (mZVI-AHB) are often believed to show greater potential than the single abiotic or biotic systems in remediating chlorinated aliphatic hydrocarbon-contaminated groundwater. However, our understanding of the remediation performance of this system under real field conditions, especially by incorporating the concept of sustainable remediation, remains limited. In this study, the performances of the mZVI, H2-AHB, and mZVI-AHB systems in dechlorinating groundwater containing complex electron acceptors were compared by evaluating their removal efficiency (RE), reaction products, and electron efficiency (EE), using trichloroethylene (TCE) as the target contaminant and NO3− and SO42− as the coexisting natural electron acceptors. Ultimately, which of these systems had TCE removal superiority was dependent on the coexisting electron acceptor. mZVI-AHB and mZVI resulted in more complete dechlorination, whereas H2-AHB exhibited higher N2 selectivity in reducing NO3−. Regardless of the coexisting electron acceptor, the mZVI-alone system showed the highest EE. Finally, the sustainability concerns and applicability of the three systems were evaluated on the basis of their TCE RE, complete dechlorination ratio, N2 selectivity, EE, and cost, which were integrated into a comparison of overall benefits. Our findings provide comprehensive and insightful information on the factors that determine remediation scheme selection in real practice.

Regulation of the high-specificity Rubisco genes by the third CbbR-type regulator in a hydrogen-oxidizing bacterium Hydrogenovibriomarinus

The obligate chemolithoautotrophic bacterium, Hydrogenovibrio marinus MH-110, has three ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) isoenzymes, CbbM, CbbLS-1, and CbbLS-2, which differ in CO2/O2 specificity factor values. Expressions of CbbM and CbbLS-1 are regulated differently by transcriptional regulators of the LysR family, CbbRm and CbbR1, respectively. CbbLS-2 has the highest specificity and is induced under low CO2 conditions, but the regulator for the cbbL2S2 genes encoding CbbLS-2 remains unidentified. In this study, the cbbR2 gene encoding the third CbbR-type regulator was identified in the downstream region of the cbbL2S2 and carboxysome gene cluster via transposon mutagenesis. CO2 depletion induced the cbbR2 gene. The cbbR2 knockout mutant could not grow under low CO2 conditions and did not produce CbbLS-2. Recombinant CbbR2 protein was bound to the promoter region of the cbbL2S2 genes. These results indicate that CbbR2 is the specific regulator for CbbLS-2 expression.

Salinity impact on the metabolic and taxonomic profiles of acid and alkali treated inoculum for hydrogen production from food waste

This study evaluated the combined impact of salinity (2.5, 13, and 19.3 g NaCl/L) and inoculum pretreatment (acid/alkali) on the genomic and metabolic profiles of mesophilic fermentative bacteria for hydrogen (H2) production from food waste. Experimental results revealed that acid-treated inoculum showed the highest H2 yield (201.12 ± 13.84 mL H2/g of volatile solids added) under medium salinity levels compared to other experimental conditions. A 7–56% increase in H2 yield was observed for pretreated inoculum than untreated inoculum. Genomic analysis and metabolic pattern revealed that the H2 production was mainly through Clostridial-type fermentation under medium to high salinity levels, whereas Enterococcus-type fermentation under low salinity levels. Further, the genomic analysis uncovered that phyla Firmicutes (69.71–96.81%) and genus Clostridium sensu stricto 1 (33.28–94.04%) dominated during the exponential gas production phase. Overall, this study showed the significance of inoculum pretreatment for the bioconversion of food waste at different salinity levels.

Microbial conversion of syngas to single cell protein: The role of carbon monoxide

Syngas has been widely utilized as substrate in microbial processes to produce various high-value products. Nevertheless, its applicability for single cell protein (SCP) production by hydrogen-oxidizing bacteria (HOB) has never been explored. Especially, the role of carbon monoxide in SCP synthesis is unknown. Thus, this study first investigated the effect of different CO and H2 ratios in syngas on Cupriavidus necator H16 growth and SCP production. The growth of C. necator H16 was significantly restrained with the increase of CO content, and it almost ceased once the CO:H2 ratios were above 1. In addition, the growth rate of C. necator H16 increased with the increase of shaking frequency and inoculum volume. Furthermore, larger gas–liquid interfacial areas and gas input amount resulted in a higher growth rate and OD value. The raw protein contents were around 50–60% regardless of CO concentration, and the amino acid profiles showed no apparent differences. The results showed that although the presence of CO led to the reduction of the growth rate of C. necator H16, it had a limited effect on the SCP quality. H2 and CO2 in syngas were the primary substrates for SCP production, while CO served more as a toxic inhibitor. The successful demonstration of SCP synthesis from syngas may provide a superior route for the valorization of waste biomass by turning it into food or feed.

Electro-cultivation of hydrogen-oxidizing bacteria to accumulate ammonium and carbon dioxide into protein-rich biomass

Hydrogen-oxidizing bacteria (HOBs) are prime candidates for the sustainable production of microbial protein because of their high nutritional value and simple metabolic requirements, which could allow a simple resource recycling of NH4+ and CO2 into a valuable product. The modality of hydrogen production/supply to HOBs represents a challenge. In this work, bioelectrochemical hydrogen and oxygen productions were coupled with HOBs cultivation in the same reactor. Using this approach, the protein content was 59 ± 8% with Hydrogenophaga and Xanthobacter as the most abundant HOBs. Biomass concentration was found to be dependent of the current density with bulk liquid biomass increasing between 101 and 124 mg TSS·L−1 for an increase of 0.1 mA·cm−2. Electrodes directly immersed in the bioreactor promoted biofilm formation on the electrode surface, which could become an attractive alternative for biomass harvesting. The results of this work establish a novel proof-of-concept for bio-electro production of microbial protein.

Coupling microscale zero-valent iron and autotrophic hydrogen-bacteria provides a sustainable remediation solution for trichloroethylene-contaminated groundwater: Mechanisms, regulation, and engineering implications

Coupling microscale zero-valent iron (mZVI) and autotrophic hydrogen bacteria (AHB) has gained increasing attention owing to its potential to improve dechlorination performance by bridging H2 donors and acceptors. However, few studies have attempted to test its sustainable remediation performance and to comprehensively unveil the governing mechanisms. This study systematically compared the performances of different systems (mZVI, H2-AHB, and mZVI-AHB) for trichloroethylene (TCE) removal, and further optimized dechlorination and H2 evolution of mZVI-AHB synchronously by regulating the mZVI particle size and dosage to achieve a win-win remediation solution. The final removal efficiency and removal rate of TCE by mZVI-AHB were 1.67-fold and 5.30-fold of those by mZVI alone respectively, and mZVI-AHB resulted in more complete dechlorination than H2-AHB alone. Combining H2 evolution kinetics, material characterization data, and bacterial community analysis results, the improved dechlorination performance of mZVI-AHB was mainly due to the following mechanisms: H2 generated by mZVI corrosion was efficiently utilized by AHB, lasting corrosion of mZVI was facilitated by AHB, and dechlorination functional bacteria were highly enriched by mZVI. Finally, the remediation performance of mZVI-AHB with different mZVI particle sizes and dosages was evaluated comprehensively in terms of dechlorination reactivity, H2 utilization efficiency and chemical cost, and suggestions for possible engineering applications are provided.

From renewable energy to sustainable protein sources: Advancement, challenges, and future roadmaps

The concerns over food security and protein scarcity, driven by population increase and higher standards of living, have pushed scientists toward finding new protein sources. A considerable proportion of resources and agricultural lands are currently dedicated to proteinaceous feed production to raise livestock and poultry for human consumption. The 1st generation of microbial protein (MP) came into the market as land-independent proteinaceous feed for livestock and aquaculture. However, MP may be a less sustainable alternative to conventional feeds, such as soybean meal and fishmeal, because this technology currently requires natural gas and synthetic chemicals. These challenges have directed researchers toward the production of 2nd generation MP by integrating renewable energies, anaerobic digestion, nutrient recovery, biogas cleaning and upgrading, carbon-capture technologies, and fermentation. The fermentation of methane-oxidizing bacteria (MOB) and hydrogen-oxidizing bacteria (HOB), i.e., two protein rich microorganisms, has shown a great potential, on the one hand, to upcycle effluents from anaerobic digestion into protein rich biomass, and on the other hand, to be coupled to renewable energy systems under the concept of Power-to-X.This work compares various production routes for 2nd generation MP by reviewing the latest studies conducted in this context and introducing the state-of-the-art technologies, hoping that the findings can accelerate and facilitate upscaling of MP production. The results show that 2nd generation MP depends on the expansion of renewable energies. In countries with high penetration of renewable electricity, such as Nordic countries, off-peak surplus electricity can be used within MP-industry by supplying electrolytic H2, which is the driving factor for both MOB and HOB-based MP production. However, nutrient recovery technologies are the heart of the 2nd generation MP industry as they determine the process costs and quality of the final product. Although huge attempts have been made to date in this context, some bottlenecks such as immature nutrient recovery technologies, less efficient fermenters with insufficient gas-to-liquid transfer, and costly electrolytic hydrogen production and storage have hindered the scale up of MP production. Furthermore, further research into techno-economic feasibility and life cycle assessment (LCA) of coupled technologies is still needed to identify key points for improvement and thereby secure a sustainable production system.

Aerobic Hydrogen-oxidizing Bacteria and Utilization for Carbon Recycle and Reduction

Aerobic Hydrogen-oxidizing Bacteria and Utilization for Carbon Recycle and Reduction

Sustainable treatment of nitrate-containing wastewater by an autotrophic hydrogen-oxidizing bacterium

Bacteria are key denitrifiers in the reduction of nitrate (NO3−-N), which is a contaminant in wastewater treatment plants (WWTPs). They can also produce carbon dioxide (CO2) and nitrous oxide (N2O). In this study, the autotrophic hydrogen-oxidizing bacterium Rhodoblastus sp. TH20 was isolated for sustainable treatment of NO3−-N in wastewater. Efficient removal of NO3−-N and recovery of biomass nitrogen were achieved. Up to 99% of NO3−-N was removed without accumulation of nitrite and N2O, consuming CO2 of 3.25 mol for each mole of NO3−-N removed. The overall removal rate of NO3−-N reached 1.1 mg L−1 h−1 with a biomass content of approximately 0.71 g L−1 within 72 h. TH20 participated in NO3−-N assimilation and aerobic denitrification. Results from 15N-labeled-nitrate test indicated that removed NO3−-N was assimilated into organic nitrogen, showing an assimilation efficiency of 58%. Seventeen amino acids were detected, accounting for 43% of the biomass. Nitrogen loss through aerobic denitrification was only approximately 42% of total nitrogen. This study suggests that TH20 can be applied in WWTP facilities for water purification and production of valuable biomass to mitigate CO2 and N2O emissions.

Life cycle assessment of plant cell cultures

A novel food such as plant cell culture (PCC) is an important complementary asset for traditional agriculture to tackle global food insecurity. To evaluate environmental impacts of PCC, a life cycle assessment was applied to tobacco bright yellow-2 and cloudberry PCCs. Global warming potential (GWP), freshwater eutrophication potential (FEUP), marine eutrophication potential, terrestrial acidification potential (TAP), stratospheric ozone depletion, water consumption and land use were assessed. The results showed particularly high contributions (82–93%) of electricity consumption to GWP, FEUP and TAP. Sensitivity analysis indicated that using wind energy instead of the average Finnish electricity mix reduced the environmental impacts by 34–81%. Enhancement in the energy efficiency of bioreactor mixing processes and reduction in cultivation time also effectively improved the environmental performance (4–47% reduction of impacts). In comparison with other novel foods, the environmental impacts of the PCC products studied were mostly comparable to those of microalgae products but higher than those of microbial protein products produced by autotrophic hydrogen-oxidizing bacteria. Assayed fresh PCC products were similar or close to GWP of conventionally grown food products and, with technological advancements, can be highly competitive.

Biosynthesis of Poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) from CO2 by a Recombinant Cupriavidusnecator.

The copolyester of 3-hydroxybutyrate (3HB) and 3-hydoxyhexanoate (3HHx), PHBHHx, is one of the most practical kind of bacterial polyhydroxyalkanoates due to its high flexibility and marine biodegradability. PHBHHx is usually produced from vegetable oils or fatty acids through β-oxidation, whereas biosynthesis from sugars has been achieved by recombinant strains of hydrogen-oxidizing bacterium Cupriavidus necator. This study investigated the biosynthesis of PHBHHx from CO2 as the sole carbon source by engineered C. necator strains. The recombinant strains capable of synthesizing PHBHHx from fructose were cultivated in a flask using complete mineral medium and a substrate gas mixture (H2/O2/CO2 = 8:1:1). The results of GC and 1H NMR analyses indicated that the recombinants of C. necator synthesized PHBHHx from CO2 with high cellular content. When 1.0 g/L (NH4)2SO4 was used as a nitrogen source, the 3HHx composition of PHBHHx in the strain MF01∆B1/pBBP-ccrMeJ4a-emd was 47.7 ± 6.2 mol%. Further investigation demonstrated that the PHA composition can be regulated by using (R)-enoyl-CoA hydratase (PhaJ) with different substrate specificity. The composition of 3HHx in PHBHHx was controlled to about 11 mol%, suitable for practical applications, and high cellular content was kept in the strains transformed with pBPP-ccrMeJAc-emd harboring short-chain-length-specific PhaJ.

Self-sustained ammonium recovery from wastewater and upcycling for hydrogen-oxidizing bacteria-based power-to-protein conversion

Microbial protein (MP) production by autotrophic hydrogen-oxidizing bacteria is regarded as a potentially sustainable approach to mitigate food crisis, water pollution, and climate change. Herein, a hybrid biological-inorganic (HBI) system which coupled energy-neutral ammonium recovery and in-situ upcycling for MP production was demonstrated. No energy and acids/bases were needed for ammonium recovery and pH control. The system was tested with different amounts of CO2 supply and operated at different operational modes (microbial fuel cell or microbial electrolysis cell mode). 0.381 g/L of biomass containing 64.79% of crude protein was produced using the recovered nitrogen and therefore led to 76.8% of ammonium recovery and 84.6% of COD removal from real municipal wastewater. The system although not yet optimal in terms of efficiency has a meaning in alleviating food crisis and environmental issues. Altogether, this study offers insight into developing an energy and resource-efficient power-to-protein process to supplement conventional food production globally.

Green electricity-driven simultaneous ammonia recovery and in-situ upcycling for microbial protein production

Currently, hydrogen-oxidizing bacteria (HOB) based power-to-protein is a promising approach to produce alternative microbial protein (MP), however, the nitrogen source used was either derived from commercial products or was firstly recovered from waste streams and then diluted for HOB growth. In the present study, simultaneous ammonium recovery from wastewater and in-situ utilization for the green MP (derived from Cupriavidus necator 335) production was successfully demonstrated using a microbial electrochemical recovery conversion cell (MERC). 0.41 ∼ 0.82 g/L of dried biomass (protein content 49 ∼ 63%) was yielded in 36 h with a power supply of 3, 4, and 5 V. C. necator 335 could grow in the MERC system receiving wastewater with a broad range of ammonium (0.05 ∼ 8 g N/L) and the highest biomass production of 0.9 g/L (protein content 54%) was achieved at 2 g N/L. 2.69 g/L of dried biomass containing 57% protein was obtained in 120 h with an initial supply of 1 L CO2 and 2 g N-NH4+. Applied voltages and ammonium concentrations showed a minor impact on the amino acid profile. Furthermore, the MERC system was tested with real waste streams (e. g., municipal wastewater, and digestate) and 0.45 ∼ 1.22 g biomass/L (protein content 52 ∼ 62%) were harvested. The characteristics of the wastewater streams (e. g., ammonium concentration and conductivity) could significantly affect the system performances. The harvested MP from real wastewater showed a high quality of amino acid profile and implied a potential in substituting traditional plant/animal-based protein.