Simon Rittmann

A comprehensive and quantitative review of dark fermentative biohydrogen production

Biohydrogen production (BHP) can be achieved by direct or indirect biophotolysis, photo-fermentation and dark fermentation, whereof only the latter does not require the input of light energy. Our motivation to compile this review was to quantify and comprehensively report strains and process performance of dark fermentative BHP. This review summarizes the work done on pure and defined co-culture dark fermentative BHP since the year 1901. Qualitative growth characteristics and quantitative normalized results of H2 production for more than 2000 conditions are presented in a normalized and therefore comparable format to the scientific community.Statistically based evidence shows that thermophilic strains comprise high substrate conversion efficiency, but mesophilic strains achieve high volumetric productivity. Moreover, microbes of Thermoanaerobacterales (Family III) have to be preferred when aiming to achieve high substrate conversion efficiency in comparison to the families Clostridiaceae and Enterobacteriaceae.The limited number of results available on dark fermentative BHP from fed-batch cultivations indicates the yet underestimated potential of this bioprocessing application. A Design of Experiments strategy should be preferred for efficient bioprocess development and optimization of BHP aiming at improving medium, cultivation conditions and revealing inhibitory effects. This will enable comparing and optimizing strains and processes independent of initial conditions and scale.

Nitrososphaera viennensis gen. nov., sp. nov., an aerobic and mesophilic, ammonia-oxidizing archaeon from soil and a member of the archaeal phylum Thaumarchaeota

A mesophilic, neutrophilic and aerobic, ammonia-oxidizing archaeon, strain EN76T, was isolated from garden soil in Vienna (Austria). Cells were irregular cocci with a diameter of 0.6–0.9 µm and possessed archaella and archaeal pili as cell appendages. Electron microscopy also indicated clearly discernible areas of high and low electron density, as well as tubule-like structures. Strain EN76T had an S-layer with p3 symmetry, so far only reported for members of the Sulfolobales. Crenarchaeol was the major core lipid. The organism gained energy by oxidizing ammonia to nitrite aerobically, thereby fixing CO2, but growth depended on the addition of small amounts of organic acids. The optimal growth temperature was 42 °C and the optimal pH was 7.5, with ammonium and pyruvate concentrations of 2.6 and 1 mM, respectively. The genome of strain EN76T had a DNA G+C content of 52.7 mol%. Phylogenetic analyses of 16S rRNA genes showed that strain EN76T is affiliated with the recently proposed phylum Thaumarchaeota, sharing 85 % 16S rRNA gene sequence identity with the closest cultivated relative ‘Candidatus Nitrosopumilus maritimus’ SCM1, a marine ammonia-oxidizing archaeon, and a maximum of 81 % 16S rRNA gene sequence identity with members of the phyla Crenarchaeota and Euryarchaeota and any of the other recently proposed phyla (e.g. ‘Korarchaeota’ and ‘Aigarchaeota’). We propose the name Nitrososphaera viennensis gen. nov., sp. nov. to accommodate strain EN76T. The type strain of Nitrososphaera viennensis is strain EN76T ( = DSM 26422T = JMC 19564T). Additionally, we propose the family Nitrososphaeraceae fam. nov., the order Nitrososphaerales ord. nov. and the class Nitrososphaeria classis nov.

Essential prerequisites for successful bioprocess development of biological CH4 production from CO2 and H2

Abstract The production and storage of energy from renewable resources steadily increases in importance. One opportunity is to utilize carbon dioxide (CO2)-type hydrogenotrophic methanogens, which are an intriguing group of microorganisms from the domain Archaea, for conversion of hydrogen and CO2 to methane (CH4). This review summarizes the current state of the art of bioprocess development for biological CH4 production (BMP) from pure cultures with pure gasses. The prerequisites for successful quantification of BMP by using closed batch, as well as fed-batch and chemostat culture cultivation, are presented. This review shows that BMP is currently a much underexplored field of bioprocess development, which mainly focuses on the application of continuously stirred tank reactors. However, some promising alternatives, such as membrane reactors have already been adapted for BMP. Moreover, industrial-based scale-up of BMP to pilot scale and larger has not been conducted. Most crucial parameters have been found to be those, which influence gas-limitation fundamentals, or parameters that contribute to the complex effects that arise during medium development for scale-up of BMP bioprocesses, highly stressing the importance of holistic BMP quantification by the application of well-defined physiological parameters. The much underexplored number of different genera, which is mainly limited to Methanothermobacter spp., offers the possibility of additional scientific and bioprocess development endeavors for the investigation of BMP. This indicates the large potential for future bioprocess development considering the possible application of bioprocessing technological aspects for renewable energy storage and power generation.

Dynamic process conditions in bioprocess development

In this review, we summarise recent studies that purposefully employed dynamic conditions, such as shifts, pulses, ramps and oscillations, for fast physiological strain characterisation and bioprocess development. We show the broad applicability of dynamic conditions and the various objectives that can thereby be investigated in a short time. Dynamic processes reveal information about the analysed system faster than traditional strategies, like continuous cultivations, as process parameters can directly be linked to platform and product parameters. Furthermore, we demonstrate that dynamic operations can result in increased productivity and high product quality, making this strategy a valuable tool for bioprocess development. With this review, we would like to encourage bioprocess engineers to an increased use of dynamic conditions in bioprocess development.

Method for assessing the impact of emission gasses on physiology and productivity in biological methanogenesis

This contribution presents a method for quantification of the impact of emission gasses on the methane production with hydrogenotrophic methanogenic archaea. The developed method allows a robust quantification of the influence of real gasses on the volumetric productivity of methanogenic cultures by uncoupling physiological and mass transfer effects. This is achieved over reference experiments with pure H2 and CO2, simulating the mass transfer influence of the non-convertible side components by addition of N2 to the reactant stream. Furthermore, this method was used to examine the performance of Methanothermobacter marburgensis on different emission gasses. None of the present side components had a negative effect on the volumetric methane production rate. The presented method showed to be ready to use as a generic tool for feasibility studies and quantification of the physiological impact regarding the use of exhaust gasses as reactant gas for the biological methanogenesis.

One-carbon substrate-based biohydrogen production: Microbes, mechanism, and productivity

Among four basic mechanisms for biological hydrogen (H2) production, dark fermentation has been considered to show the highest hydrogen evolution rate (HER). H2 production from one-carbon (C1) compounds such as formate and carbon monoxide (CO) is promising because formate is an efficient H2 carrier, and the utilization of CO-containing syngas or industrial waste gas may render the industrial biohydrogen production process cost-effective. A variety of microbes with the formate hydrogen lyase (FHL) system have been identified from phylogenetically diverse groups of archaea and bacteria, and numerous efforts have been undertaken to improve the HER for formate through strain optimization and bioprocess development. CO-dependent H2 production has been investigated to enhance the H2 productivity of various carboxydotrophs via an increase in CO gas-liquid mass transfer rates and the construction of genetically modified strains. Hydrogenogenic CO-conversion has been applied to syngas and by-product gas of the steel-mill process, and this low-cost feedstock has shown to be promising in the production of biomass and H2. Here, we focus on recent advances in the isolation of novel phylogenetic groups utilizing formate or CO, the remarkable genetic engineering that enhances H2 productivity, and the practical implementation of H2 production from C1 substrates.

Biofuels and CO2 neutrality: an opportunity

CO2-neutral bioprocesses are of immanent concern and can be coupled by using integrated bioprocess and biofuel production systems. Existing biofuel generations are, therefore, reclassified according to the current possible bioprocessing routes. Only the first biofuel generation has been successfully carried into a commercial scale, while the second is still being improved at laboratory scale or in pilot-scale processes. Biodiesel and biohydrogen, as third- and fourth-generation biofuels, respectively, are also being studied at the laboratory scale. Here, we introduce the fifth biofuel generation, which is based on biological CH4 production from gaseous raw materials. The integration of bioprocess systems and the coupling between different biofuel generations under CO2 neutrality is analyzed and presented to be of great interest for industry and science. Value-added production (i.e., recombinant proteins) can be coupled to CO2-neutral integrated biofuel production systems and, hence, integration of different biofuel generations within a biorefinery concept could be translated into a reality.

Assessing the Ecophysiology of Methanogens in the Context of Recent Astrobiological and Planetological Studies

Among all known microbes capable of thriving under extreme and, therefore, potentially extraterrestrial environmental conditions, methanogens from the domain Archaea are intriguing organisms. This is due to their broad metabolic versatility, enormous diversity, and ability to grow under extreme environmental conditions. Several studies revealed that growth conditions of methanogens are compatible with environmental conditions on extraterrestrial bodies throughout the Solar System. Hence, life in the Solar System might not be limited to the classical habitable zone. In this contribution we assess the main ecophysiological characteristics of methanogens and compare these to the environmental conditions of putative habitats in the Solar System, in particular Mars and icy moons. Eventually, we give an outlook on the feasibility and the necessity of future astrobiological studies concerning methanogens.

A Critical Assessment of Microbiological Biogas to Biomethane Upgrading Systems

Microbiological biogas upgrading could become a promising technology for production of methane (CH(4)). This is, storage of irregular generated electricity results in a need to store electricity generated at peak times for use at non-peak times, which could be achieved in an intermediate step by electrolysis of water to molecular hydrogen (H(2)). Microbiological biogas upgrading can be performed by contacting carbon dioxide (CO(2)), H(2) and hydrogenotrophic methanogenic Archaea either in situ in an anaerobic digester, or ex situ in a separate bioreactor. In situ microbiological biogas upgrading is indicated to require thorough bioprocess development, because only low volumetric CH(4) production rates and low CH(4) fermentation offgas content have been achieved. Higher volumetric production rates are shown for the ex situ microbiological biogas upgrading compared to in situ microbiological biogas upgrading. However, the ex situ microbiological biogas upgrading currently suffers from H(2) gas liquid mass transfer limitation, which results in low volumetric CH(4) productivity compared to pure H(2)/CO(2) conversion to CH(4). If waste gas utilization from biological and industrial sources can be shown without reduction in volumetric CH(4) productivity, as well as if the aim of a single stage conversion to a CH(4) fermentation offgas content exceeding 95 vol% can be demonstrated, ex situ microbiological biogas upgrading with pure or enrichment cultures of methanogens could become a promising future technology for almost CO(2)-neutral biomethane production.

Identification of lily pollen 14-3-3 isoforms and their subcellular and time-dependent expression profile.

Abstract 14-3-3 proteins are major regulators in plant development and physiology including primary metabolism and signal transduction pathways, typically via a phosphorylation-dependent interaction with a target protein. Four full-length 14-3-3 isoforms were identified in pollen grains of Lilium longiflorum by screening of a cDNA library and RACE (rapid amplification of cDNA ends)-PCR. Mass spectrometry analysis of partially purified 14-3-3s confirmed the presence of the four isoforms but also indicated the presence of additional, less abundant 14-3-3 isoforms in lily pollen. Separation of partially purified 14-3-3 proteins by two-dimensional gel electrophoresis resulted in nine spots that mainly contained the four major 14-3-3 isoforms. In a first step to examine putative physiological roles of specific 14-3-3 isoforms, their subcellular expression profile during pollen germination and tube growth was monitored using a characterized set of antibodies against 14-3-3 proteins with distinct crossreactivity. The abundance profile of 14-3-3 proteins associated with the cytosol, endomembranes (tonoplast, endoplasmic reticulum, Golgi, mitochondria) and plasma membrane showed high spatial-temporal dynamics. This indicates different targets of 14-3-3 proteins at different organelles and time points during pollen germination and growth.