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Agriculture is one of the major fields, where sewage sludge can be used. Its high nutrient content can contribute to the improvement of important soil properties, such as nutrient content, water balance and soil structure. However, sewage sludge may contain hazardous components, such as pathogens and pollutants. Therefore, it is important to monitor the effects of its field application. In this paper, we assessed the impacts of two low-dose (2.5 m3/ha) municipal sewage sludge compost applications (in 2013 and in 2017) in a 5.6 ha arable land in southeast Hungary (near Újkígyós), located in the Hungarian Great Plain. The nutrient and the heavy metal contents in the upper soil layer (0-30 cm) of the studied Chernozem soils were compared between two sampling campaigns in 2013 (before the compost applications) and in 2018 (after the compost applications). Basic soil properties (pH, salinity, humus content, carbonate content, Arany yarn number) complemented with nutrient content (K2O, P2O5, NO2+ NO3) and heavy metal content (Cd, Co, Cr, Cu, Ni, Pb and Zn) analyses were performed. The results show that no significant change can be noticed in the baseline parameters over the 5-year period. The slight increase in the P2O5, NO2+ NO3 content is closely related to the beneficial effects of the sewage sludge deposition. The soil-bound heavy metal load did not increase significantly as a result of the compost treatments, only nickel showed a slight increase in the topsoil. In all cases the heavy metal concentrations did not reach the contamination thresholds set by Hungarian standards. The results provided positive evidences proving that low dose municipal sewage sludge compost disposal on agricultural land is safe, and can be considered as a sustainable soil amendment for agriculture in compliance with legal requirements.

Bioremediation provides an environmentally sound solution for hydrocarbon removal. Although bioremediation under anoxic conditions is slow, it can be coupled with methanogenesis and is suitable for energy recovery. By altering conditions and supplementing alternative terminal electron acceptors to the system to induce syntrophic partners of the methanogens, this process can be enhanced. In this study, we investigated a hydrocarbon-degrading microbial community derived from chronically contaminated soil. Various hydrocarbon mixtures were used during our experiments in the presence of different electron acceptors. In addition, we performed whole metagenome sequencing to identify the main actors of hydrocarbon biodegradation in the samples. Our results showed that the addition of ferric ions or sulphate increased the methane yield. Furthermore, the addition of CO 2 , ferric ion or sulphate enhanced the biodegradation of alkanes. A significant increase in biodegradation was observed in the presence of ferric ions or sulphate in the case of all aromatic components, while naphthalene and phenanthrene degradation was also enhanced by CO 2 . Metagenome analysis revealed that Cellulomonas sp. is the most abundant in the presence of alkanes, while Ruminococcus and Faecalibacterium spp. are prevalent in aromatics-supplemented samples. From the recovery of 25 genomes, it was concluded that the main pathway of hydrocarbon activation was fumarate addition in both Cellulomonas, Ruminococcus and Faecalibacterium. Chloroflexota bacteria can utilise the central metabolites of aromatics biodegradation via ATP-independent benzoyl-CoA reduction. KEY POINTS: • Methanogenesis and hydrocarbon biodegradation were enhanced by Fe 3+ or SO4 2- • Cellulomonas, Ruminococcus and Faecalibacterium can be candidates for the main hydrocarbon degraders • Chloroflexota bacteria can utilise the central metabolites of aromatics degradation., (© 2024. The Author(s).)

Plastics have revolutionised human industries, thanks to their versatility and durability. However, their extensive use, coupled with inadequate waste disposal, has resulted in plastic becoming ubiquitous in every environmental compartment, posing potential risks to the economy, human health and the environment. Additionally, under natural conditions, plastic waste breaks down into microplastics (MPs<5 mm). The increasing quantity of MPs exerts a significant burden on the soil environment, particularly in agroecosystems, presenting a new stressor for soil-dwelling organisms. In this review, we delve into the effects of MP pollution on soil ecosystems, with a specific attention to (a) MP transport to soils, (b) potential changes of MPs under environmental conditions, (c) and their interaction with the physical, chemical and biological components of the soil. We aim to shed light on the alterations in the distribution, activity, physiology and growth of soil flora, fauna and microorganisms in response to MPs, offering an ecotoxicological perspective for environmental risk assessment of plastics. The effects of MPs are strongly influenced by their intrinsic traits, including polymer type, shape, size and abundance. By exploring the multifaceted interactions between MPs and the soil environment, we provide critical insights into the consequences of plastic contamination. Despite the growing body of research, there remain substantial knowledge gaps regarding the long-term impact of MPs on the soil. Our work underscores the importance of continued research efforts and the adoption of standardised approaches to address plastic pollution and ensure a sustainable future for our planet., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 The Authors. Published by Elsevier Inc. All rights reserved.)

Six different TiO 2 /CNT nanocomposite-coated polyvinylidene-fluoride (PVDF) microfilter membranes (including -OH or/and -COOH functionalized CNTs) were evaluated in terms of their performance in filtering oil-in-water emulsions. In the early stages of filtration, until reaching a volume reduction ratio (VRR) of ~1.5, the membranes coated with functionalized CNT-containing composites provided significantly higher fluxes than the non-functionalized ones, proving the beneficial effect of the surface modifications of the CNTs. Additionally, until the end of the filtration experiments (VRR = 5), notable flux enhancements were achieved with both TiO 2 (~50%) and TiO 2 /CNT-coated membranes (up to ~300%), compared to the uncoated membrane. The irreversible filtration resistances of the membranes indicated that both the hydrophilicity and surface charge (zeta potential) played a crucial role in membrane fouling. However, a sharp and significant flux decrease (~90% flux reduction ratio) was observed for all membranes until reaching a VRR of 1.1-1.8, which could be attributed to the chemical composition of the oil. Gas chromatography measurements revealed a lack of hydrocarbon derivatives with polar molecular fractions (which can act as natural emulsifiers), resulting in significant coalescent ability (and less stable emulsion). Therefore, this led to a more compact cake layer formation on the surface of the membranes (compared to a previous study). It was also demonstrated that all membranes had excellent purification efficiency (97-99.8%) regarding the turbidity, but the effectiveness of the chemical oxygen demand reduction was slightly lower, ranging from 93.7% to 98%.

Plastics have inundated the world, with microplastics (MPs) being small particles, less than 5 mm in size, originating from various sources. They pervade ecosystems such as freshwater and marine environments, soils, and the atmosphere. MPs, due to their small size and strong adsorption capacity, pose a threat to plants by inhibiting seed germination, root elongation, and nutrient absorption. The accumulation of MPs induces oxidative stress, cytotoxicity, and genotoxicity in plants, which also impacts plant development, mineral nutrition, photosynthesis, toxic accumulation, and metabolite production in plant tissues. Furthermore, roots can absorb nanoplastics (NPs), which are then distributed to stems, leaves, and fruits. As MPs and NPs harm organisms and ecosystems, they raise concerns about physical damage and toxic effects on animals, and the potential impact on human health via food webs. Understanding the environmental fate and effects of MPs is essential, along with strategies to reduce their release and mitigate consequences. However, a full understanding of the effects of different plastics, whether traditional or biodegradable, on plant development is yet to be achieved. This review offers an up-to-date overview of the latest known effects of plastics on plants.

Personal protective equipment, used extensively during the COVID-19 pandemic, heavily burdened the environment due to improper waste management. Owing to their fibrous structure, layered non-woven polypropylene (PP) disposable masks release secondary fragments at a much higher rate than other plastic waste types, thus, posing a barely understood new form of ecological hazard. Here we show that PP mask fragments of different sizes induce morphogenic responses in plants during their early development. Using in vitro systems and soil-filled rhizotrons, we found that several PP mask treatments modified the root growth of Brassica napus (L.) regardless of the experimental system. The environment around the root and mask fragments seemed to influence the effect of PP fabric fragment contamination on early root growth. In soil, primary root length was clearly inhibited by larger PP mask fragments at 1 % concentration, while the two smallest sizes of applied mask fragments caused distinct, concentration-dependent changes in the lateral root numbers. Our results indicate that PP can act as a stressor: contamination by PP surgical masks affects plant growth and hence, warrants attention. Further investigations regarding the effects of plastic pollution on plant-soil interactions involving various soil types are urgently needed., (Copyright © 2022 The Authors. Published by Elsevier B.V. All rights reserved.)

Chronic pollution by used lubricant oils (ULOs) poses a serious challenge to the environment. Under stress conditions, microorganisms, including potential degraders, can enter a viable but non-culturable (VBNC) state, complicating the bioremediation of ULO-polluted areas. Resuscitation-promoting factors (Rpfs) can reverse this transition and/or enhance the biodegradation performance of both native and augmented strains. Here, Rpf-containing extracellular organic matter (EOM) from Micrococcus luteus was used to enhance the ex situ ULO removal in biostimulated and bioaugmented (with Rhodococcus qingshengii KAG C, R. erythropolis PR4) soils. ULO bioconversion, microbial activity, and CFUs were significantly higher in EOM-treated soils compared to corresponding control soils. After 60 days, the initial ULO concentration (52,500 mg kg -1 ) was reduced by 37% and 45% with EOM-supplemented biostimulation and bioaugmentation, respectively. Based on high-throughput 16S rRNA analysis, the enhancement was attributable both to the reactivation of EOM-responsive hydrocarbonoclastic bacterial genera (e.g., Pseudomonas, Comamonas, Stenotrophomonas, Gordonia) and to the long-term positive effect of EOM on the degradative efficacy of the introduced rhodococci. Ecotoxicological responses revealed that reduced ULO concentration did not correlate with decreased soil toxicity. Our findings provide an insight into the applicability of EOM in bioremediation and its effects on the soil microbial activity and community composition., (Copyright © 2021 The Authors. Published by Elsevier B.V. All rights reserved.)

The accumulation of petroleum hydrocarbons in the environment substantially endangers terrestrial and aquatic ecosystems. Many microbial strains have been recognized to utilize aliphatic and aromatic hydrocarbons under aerobic conditions. Nevertheless, most of these pollutants are transferred by natural processes, including rain, into the underground anaerobic zones where their degradation is much more problematic. In oxic zones, anaerobic microenvironments can be formed as a consequence of the intensive respiratory activities of (facultative) aerobic microbes. Even though aerobic bioremediation has been well-characterized over the past few decades, ample research is yet to be done in the field of anaerobic hydrocarbon biodegradation. With the emergence of high-throughput techniques, known as omics (e.g., genomics and metagenomics), the individual biodegraders, hydrocarbon-degrading microbial communities and metabolic pathways, interactions can be described at a contaminated site. Omics approaches provide the opportunity to examine single microorganisms or microbial communities at the system level and elucidate the metabolic networks, interspecies interactions during hydrocarbon mineralization. Metatranscriptomics and metaproteomics, for example, can shed light on the active genes and proteins and functional importance of the less abundant species. Moreover, novel unculturable hydrocarbon-degrading strains and enzymes can be discovered and fit into the metabolic networks of the community. Our objective is to review the anaerobic hydrocarbon biodegradation processes, the most important hydrocarbon degraders and their diverse metabolic pathways, including the use of various terminal electron acceptors and various electron transfer processes. The review primarily focuses on the achievements obtained by the current high-throughput (multi-omics) techniques which opened new perspectives in understanding the processes at the system level including the metabolic routes of individual strains, metabolic/electric interaction of the members of microbial communities. Based on the multi-omics techniques, novel metabolic blocks can be designed and used for the construction of microbial strains/consortia for efficient removal of hydrocarbons in anaerobic zones., (Copyright © 2020 Laczi, Erdeiné Kis, Szilágyi, Bounedjoum, Bodor, Vincze, Kovács, Rákhely and Perei.)

Semisolid dosage forms are recommended for the dermal care of babies and children. If we look at the ingredients of these preparations, there are still many cases in which there are substances (occlusive agents, preservatives) that no longer meet certain requirements of the modern age, so it is timely to replace them with other substances. The aim of this work was to formulate a science-based formulation with new components that keep or improve its moisturizing properties, rheological parameters, and microbiological stability. Occlusive oils, like white petrolatum and liquid paraffin and the preservative parabens are traditional ingredients in oil in water creams, were replaced with white beeswax, sunflower oil, and phenoxyethanol, respectively. Cocoa butter, urea, and glycerol were added to improve long-lasting hydration and support the barrier function of the reformulated creams. The rheological properties of the formulations were determined. The effects of the preparations on skin hydration and on the barrier function of the skin were tested. Furthermore, microbiological stability was investigated. The result of the reformulation was an o/w cream that provided a good longer-lasting hydration effect; supported the barrier function of the baby skin without occlusion; and had adequate consistency, easy spreading, a pleasant skin feeling, proper pH, and good microbiological stability.

Metal-polluted areas, especially where municipal sewage is used as fertilizer, often have high concentrations of more than one metal. The development of the root system is regulated by a complex signaling network, which includes reactive oxygen and nitrogen species. The delicate balance of the endogenous signal system can be affected by various environmental stimuli including heavy metals (HMs) in excess. Our goal was to analyze the microelement homeostasis, root architecture, and to determine the underlying changes in the nitro-oxidative status in the root system of rapeseed ( Brassica napus L.) and sunflower ( Helianthus annuus L.) subjected to combined HM treatments. The effect of model-sewage in two different layouts was simulated in rhizotron system by only supplementing the highest HM concentrations (Cd, Cr, Cu, Hg, Ni, Pb, and Zn) legally allowed. The two species reacted differently to combined HM treatment; compared to the relatively sensitive sunflower, rapeseed showed better metal translocation capability and root growth even at the more severe treatment, where the pattern of protein tyrosine nitration was reorganized. The obtained results, especially the increased nitric oxide content and changed pattern of tyrosine nitration in rapeseed, can indicate acclimation and species-specific nitro-oxidative responses to combined HM stress.

Used lubricant oils (ULOs) strongly bind to soil particles and cause persistent pollution. In this study, soil microcosm experiments were conducted to model the ex situ bioremediation of a long term ULO-polluted area. Biostimulation and various inoculation levels of bioaugmentation were applied to determine the efficacy of total petrol hydrocarbon (TPH) removal. ULO-contaminated soil microcosms were monitored for microbial respiration, colony-forming units (CFUs) and TPH bioconversion. Biostimulation with inorganic nutrients was responsible for 22% of ULO removal after 40 days. Bioaugmentation using two hydrocarbon-degrader strains: Rhodococcus quingshengii KAG C and Rhodococcus erythropolis PR4 at a small inoculum size (10 7 CFUs g -1 soil), reduced initial TPH concentration by 24% and 29%, respectively; the application of a higher inoculum size (10 9 CFUs g -1 soil) led to 41% and 32% bioconversion, respectively. After 20 days, all augmented CFUs decreased to the same level as measured in the biostimulated cases, substantiating the challenge for the newly introduced hydrocarbon-degrading strains to cope with environmental stressors. Our results not only highlight that an increased number of degrader cells does not always correlate with enhanced TPH bioconversion, but they also indicate that biostimulation might be an economical solution to promote ULO biodegradation in long term contaminated soils.

Roots have a noteworthy plasticity: due to different stress conditions their architecture can change to favour seedling vigour and yield stability. The development of the root system is regulated by a complex and diverse signalling network, which besides hormonal factors, includes reactive oxygen (ROS) - and nitrogen species (RNS). The delicate balance of the endogenous signal system can be affected by various environmental stimuli, such as the excess of essential heavy metals, like zinc (Zn). Zn at low concentration, is able to induce the morphological and physiological adaptation of the root system, but in excess it exerts toxic effects on plants. In this study the effect of a low, growth-inducing, and a high, growth inhibiting Zn concentrations on the early development of Brassica napus (L.) root architecture and the underlying nitro-oxidative mechanisms were studied in a soil-filled rhizotron system. The growth-inhibiting Zn treatment resulted in elevated protein tyrosine nitration due to the imbalance in ROS and RNS homeostasis, however its pattern was not changed compared to the control. This nitro-oxidative stress was accompanied by serious changes in the cell wall composition and decrease in the cell proliferation and viability, due to the high Zn uptake and disturbed microelement homeostasis in the root tips. During the positive root growth response, a tyrosine nitration-pattern reorganisation was observed; there were no substantial changes in ROS and RNS balance and the viability and proliferation of the root tips' meristematic zone decreased to a lesser extent, as a result of a lower Zn uptake. The obtained results suggest that Zn in different amounts triggers different root growth responses accompanied by distinct changes in the pattern and strength of tyrosine nitration, proposing that nitrosative processes have an important role in the stress-induced root growth responses., (Copyright © 2019 Elsevier Inc. All rights reserved.)

Novosphingobium resinovorum SA1 was the first single isolate capable of degrading sulfanilic acid, a widely used representative of sulfonated aromatic compounds. The genome of the strain was recently sequenced, and here, we present whole-cell transcriptome analyses of cells exposed to sulfanilic acid as compared to cells grown on glucose. The comparison of the transcript profiles suggested that the primary impact of sulfanilic acid on the cell transcriptome was a starvation-like effect. The genes of the peripheral, central, and common pathways of sulfanilic acid biodegradation had distinct transcript profiles. The peripheral genes located on a plasmid had very high basal expressions which were hardly upregulated by sulfanilic acid. The genomic context and the codon usage preference of these genes suggested that they were acquired by horizontal gene transfer. The genes of the central pathways were remarkably inducible by sulfanilic acid indicating the presence of a substrate-specific regulatory system in the cells. Surprisingly, the genes of the common part of the metabolic pathway had low and sulfanilic acid-independent transcript levels. The approach applied resulted in the identification of the genes of proteins involved in auxiliary processes such as electron transfer, substrate and iron transports, sulfite oxidases, and sulfite transporters. The whole transcriptome analysis revealed that the cells exposed to xenobiotics had multiple responses including general starvation-like, substrate-specific, and substrate-related effects. From the results, we propose that the genes of the peripheral, central, and common parts of the pathway have been evolved independently.

Petroleum hydrocarbons and derivatives are widespread contaminants in both aquifers and soil, their elimination is in the primary focus of environmental studies. Microorganisms are key components in biological removal of pollutants. Strains capable to utilize hydrocarbons usually appear at the contaminated sites, but their metabolic activities are often restricted by the lack of nutrients and/or they can only utilize one or two components of a mixture. We isolated a novel Rhodococcus sp. MK1 strain capable to degrade the components of diesel oil simultaneously. The draft genome of the strain was determined and besides the chromosome, the presence of one plasmid could be revealed. Numerous routes for oxidation of aliphatic and aromatic compounds were identified. The strain was tested in ex situ applications aiming to compare alternative solutions for microbial degradation of hydrocarbons. The results of bioaugmentation and biostimulation experiments clearly demonstrated that - in certain cases - the indigenous microbial community could be exploited for bioremediation of oil-contaminated soils. Biostimulation seems to be efficient for removal of aged contaminations at lower concentration range, whereas bioaugmentation is necessary for the treatment of freshly and highly polluted sites.

Sulfanilic acid (4-aminobenzenesulfonic acid) is a sulfonated aromatic amine widely used in chemical industries for synthesis of various organic dyes and sulfa drugs. There are quite a few microbial co-cultures or single isolates capable of completely degrading this compound. Novosphingobium resinovorum SA1 was the first single bacterium which could utilize sulfanilic acid as its sole carbon, nitrogen and sulfur source. The strain has versatile catabolic routes for the bioconversion of numerous other aromatic compounds. Here, the complete genome sequence of the N. resinovorum SA1 strain is reported. The genome consists of a circular chromosome of 3.8 Mbp and four extrachromosomal elements between 67 and 1 759.8 kbp in size. Three alternative 3-ketoadipate pathways were identified on the plasmids. Sulfanilic acid is decomposed via a modified 3-ketoadipate pathway and the oxygenases involved form a phylogenetically separate branch on the tree. Sequence analysis of these elements might provide a genetic background for deeper insight into the versatile catabolic metabolism of various aromatic xenobiotics, including sulfanilic acid and its derivatives. Moreover, this is also a good model strain for understanding the role and evolution of multiple genetic elements within a single strain., (Copyright © 2016 Elsevier B.V. All rights reserved.)

Rhodococcus erythropolis PR4 is able to degrade diesel oil, normal-, iso- and cycloparaffins and aromatic compounds. The complete DNA content of the strain was previously sequenced and numerous oxygenase genes were identified. In order to identify the key elements participating in biodegradation of various hydrocarbons, we performed a comparative whole transcriptome analysis of cells grown on hexadecane, diesel oil and acetate. The transcriptomic data for the most prominent genes were validated by RT-qPCR. The expression of two genes coding for alkane-1-monooxygenase enzymes was highly upregulated in the presence of hydrocarbon substrates. The transcription of eight phylogenetically diverse cytochrome P450 (cyp) genes was upregulated in the presence of diesel oil. The transcript levels of various oxygenase genes were determined in cells grown in an artificial mixture, containing hexadecane, cycloparaffin and aromatic compounds and six cyp genes were induced by this hydrocarbon mixture. Five of them were not upregulated by linear and branched hydrocarbons. The expression of fatty acid synthase I genes was downregulated by hydrocarbon substrates, indicating the utilization of external alkanes for fatty acid synthesis. Moreover, the transcription of genes involved in siderophore synthesis, iron transport and exopolysaccharide biosynthesis was also upregulated, indicating their important role in hydrocarbon metabolism. Based on the results, complex metabolic response profiles were established for cells grown on various hydrocarbons. Our results represent a functional annotation of a rhodococcal genome, provide deeper insight into molecular events in diesel/hydrocarbon utilization and suggest novel target genes for environmental monitoring projects.

Background: Pathogens can influence allergic respiratory diseases. We previously found that multiple infections with Chlamydophila pneumoniae induce the production of interleukin-17A (IL-17A) and IL-17E, which have roles in the pathogenesis of asthma. The present work was designed to investigate our hypothesis that infections with another pathogen can induce the production of IL-17A and IL-17E., Materials and Methods: At an internal of 28 days, mice were infected twice with Chlamydia muridarum; the kinetics of IL-17A and IL-17E expression was subsequently determined at the mRNA and protein levels. The amounts of IL-17 cytokines produced by the stimulated spleen cells were determined by enzyme-linked immunosorbent assay (ELISA). The presence of IL-17E in the lungs was revealed by an indirect immunofluorescence test., Results: The infection with C. muridarum induced the production of IL-17A at the early stages of infection. The quantity of IL-17E was highest on days 28 and 56 after the first infection (28 days after the second infection). In the later stages of infection, IL-17E was produced by epithelial cells. The re-stimulated peripheral spleen cells produced IL-17A., Conclusion: Multiple infection with C. muridarum induces the production of a high amount of IL-17E, which plays an important part in the pathogenesis of allergic pulmonary diseases.

A bacterium capable to grow on sulfanilic acid as sole carbon, nitrogen and sulfur source has been isolated. A unique feature of this strain is that it contains the full set of enzymes necessary for the biodegradation of sulfanilic acid. Taxonomical analysis identified our isolate as Sphingomonas subaretica SA1 sp. The biodegradation pathway of sulfanilic acid was investigated at the molecular level. Screening the substrate specificity of the strain disclosed its capacity to degrade six analogous aromatic compounds including p-aminobenzoic acid. Moreover, the strain was successfully used for removal of oil contaminations. S. subarctica SA1 seemed to use distinct enzyme cascades for decomposition of these molecules, since alternative enzymes were induced in cells grown on various substrates. However, the protein patterns appearing upon induction by sulfanilic acid and sulfocatechol were very similar to each other indicating common pathways for the degradation of these substrates. Cells grown on sulfanilic acid could convert p-aminobenzoic acid to some extent and vice versa. Two types of ring cleaving dioxygenases were detected in the cells grown on various substrates: one preferred protocatechol, while the other had higher activity with sulfocatechol. This latter enzyme, named as sulfocatechol dioxygenase was partially purified and characterized.

A two-stage fermentation system was constructed to test and demonstrate the feasibility of biohydrogen generation from keratin-rich biowaste. We isolated a novel aerobic Bacillus strain (Bacillus licheniformis KK1) that displays outstanding keratinolytic activity. The isolated strain was employed to convert keratin-containing biowaste into a fermentation product that is rich in amino acids and peptides. The process was optimized for the second fermentation step, in which the product of keratin fermentation--supplemented with essential minerals--was metabolized by Thermococcus litoralis, an anaerobic hyperthermophilic archaeon. T. litoralis grew on the keratin hydrolysate and produced hydrogen gas as a physiological fermentation byproduct. Hyperthermophilic cells utilized the keratin hydrolysate in a similar way as their standard nutrient, i.e., bacto-peptone. The generalization of the findings to protein-rich waste treatment and production of biohydrogen is discussed and possible means of further improvements are listed.

A fundamental and principal difficulty of the future energy supply is that the formation of fossil fuels is much slower than the rate of their exploitation. Therefore the reserves which can be recovered in an energetically feasible manner are shrinking parallel with an increasing world-wide energy demand. Among the alternative energy carriers, hydrogen is preferred because it is easy to transport and store and it burns to environmentally friendly water vapour when utilized. Hydrogen can be produced in biological systems, however, our understanding of the molecular details is just emerging.