Temperature Compensation in Methanosarcina barkeri by Modulation of Hydrogen and Acetate Affinity

Effect of model methanogens on the electrochemical activity, stability, and microbial community structure of Geobacter spp. dominated biofilm anodes

Combining anaerobic digestion (AD) and microbial electrochemical technologies (MET) in AD-MET holds great potential. Methanogens have been identified as one cause of decreased electrochemical activity and deterioration of Geobacter spp. biofilm anodes. A better understanding of the different interactions between methanogenic genera/species and Geobacter spp. biofilms is needed to shed light on the observed reduction in electrochemical activity and stability of Geobacter spp. dominated biofilms as well as observed changes in microbial communities of AD-MET. Here, we have analyzed electrochemical parameters and changes in the microbial community of Geobacter spp. biofilm anodes when exposed to three representative methanogens with different metabolic pathways, i.e., Methanosarcina barkeri, Methanobacterium formicicum, and Methanothrix soehngenii. M. barkeri negatively affected the performance and stability of Geobacter spp. biofilm anodes only in the initial batches. In contrast, M. formicicum did not affect the stability of Geobacter spp. biofilm anodes but caused a decrease in maximum current density of ~37%. M. soehngenii induced a coloration change of Geobacter spp. biofilm anodes and a decrease in the total transferred charge by ~40%. Characterization of biofilm samples after each experiment by 16S rRNA metabarcoding, whole metagenome nanopore sequencing, and shotgun sequencing showed a higher relative abundance of Geobacter spp. after exposure to M. barkeri as opposed to M. formicicum or M. soehngenii, despite the massive biofilm dispersal observed during initial exposure to M. barkeri.

Electrical current disrupts the electron transfer in defined consortia

Improving methane production through electrical current application to anaerobic digesters has garnered interest in optimizing such microbial electrochemical technologies, with claims suggesting direct interspecies electron transfer (DIET) at the cathode enhances methane yield. However, previous studies with mixed microbial communities only reported interspecies interactions based on species co-occurrence at the cathode, lacking insight into how a poised cathode influences well-defined DIET-based partnerships. To address this, we investigated the impact of continuous and discontinuous exposure to a poised cathode (-0.7 V vs. standard hydrogen electrode) on a defined consortium of Geobacter metallireducens and Methanosarcina barkeri, known for their DIET capabilities. The physiology of DIET consortia exposed to electrical current was compared to that of unexposed consortia. In current-exposed incubations, overall metabolic activity and cell numbers for both partners declined. The consortium, receiving electrons from the poised cathode, accumulated acetate and hydrogen, with only 32% of the recovered electrons allocated to methane production. Discontinuous exposure intensified these detrimental effects. Conversely, unexposed control reactors efficiently converted ethanol to methane, transiently accumulating acetate and recovering 88% of electrons in methane. Our results demonstrate the overall detrimental effect of electrochemical stimulation on a DIET consortium. Besides, the data indicate that the presence of an alternative electron donor (cathode) hinders efficient electron retrieval by the methanogen from Geobacter, and induces catabolic repression of oxidative metabolism in Geobacter. This study emphasizes understanding specific DIET-based interactions to enhance methane production during electrical stimulation, providing insights for optimizing tailored interspecies partnerships in microbial electrochemical technologies.

Metabolomic rearrangement controls the intrinsic microbial response to temperature changes

Temperature is one of the key determinants of microbial behavior and survival, whose impact is typically studied under heat- or cold-shock conditions that elicit specific regulation to combat lethal stress. At intermediate temperatures, cellular growth rate varies according to the Arrhenius law of thermodynamics without stress responses, a behavior whose origins have not yet been elucidated. Using single-cell microscopy during temperature perturbations, we show that bacteria exhibit a highly conserved, gradual response to temperature upshifts with a time scale of ~1.5 doublings at the higher temperature, regardless of initial/final temperature or nutrient source. We find that this behavior is coupled to a temperature memory, which we rule out as being neither transcriptional, translational, nor membrane dependent. Instead, we demonstrate that an autocatalytic enzyme network incorporating temperature-sensitive Michaelis-Menten kinetics recapitulates all temperature-shift dynamics through metabolome rearrangement, which encodes a temperature memory and successfully predicts alterations in the upshift response observed under simple-sugar, low-nutrient conditions, and in fungi. This model also provides a mechanistic framework for both Arrhenius-dependent growth and the classical Monod Equation through temperature-dependent metabolite flux.

Complexity of temperature dependence in methanogenic microbial environments

There is virtually no environmental process that is not dependent on temperature. This includes the microbial processes that result in the production of CH₄, an important greenhouse gas. Microbial CH₄ production is the result of a combination of many different microorganisms and microbial processes, which together achieve the mineralization of organic matter to CO₂ and CH₄. Temperature dependence applies to each individual step and each individual microbe. This review will discuss the different aspects of temperature dependence including temperature affecting the kinetics and thermodynamics of the various microbial processes, affecting the pathways of organic matter degradation and CH₄ production, and affecting the composition of the microbial communities involved. For example, it was found that increasing temperature results in a change of the methanogenic pathway with increasing contribution from mainly acetate to mainly H₂/CO₂ as immediate CH₄ precursor, and with replacement of aceticlastic methanogenic archaea by thermophilic syntrophic acetate-oxidizing bacteria plus thermophilic hydrogenotrophic methanogenic archaea. This shift is consistent with reaction energetics, but it is not obligatory, since high temperature environments exist in which acetate is consumed by thermophilic aceticlastic archaea. Many studies have shown that CH₄ production rates increase with temperature displaying a temperature optimum and a characteristic apparent activation energy (E_a). Interestingly, CH₄ release from defined microbial cultures, from environmental samples and from wetland field sites all show similar E_a values around 100 kJ mol^-1 indicating that CH₄ production rates are limited by the methanogenic archaea rather than by hydrolysis of organic matter. Hence, the final rather than the initial step controls the methanogenic degradation of organic matter, which apparently is rarely in steady state.

Methane emissions from macrophyte beach wrack on Baltic seashores

Beach wrack of marine macrophytes is a natural component of many beaches. To test if such wrack emits the potent greenhouse gas methane, field measurements were made at different seasons on beach wrack depositions of different ages, exposure, and distance from the water. Methane emissions varied greatly, from 0 to 176 mg CH₄-C m^-2 day^-1, with a clear positive correlation between emission and temperature. Dry wrack had lower emissions than wet. Using temperature data from 2016 to 2020, seasonal changes in fluxes were calculated for a natural wrack accumulation area. Such calculated average emissions were close to zero during winter, but peaked in summer, with very high emissions when daily temperatures exceeded 20 °C. We conclude that waterlogged beach wrack significantly contributes to greenhouse gas emissions and that emissions might drastically increase with increasing global temperatures. When beach wrack is collected into heaps away from the water, the emissions are however close to zero.

Methanogenesis pathways of methanogens and their responses to substrates and temperature in sediments from the South Yellow Sea

Although coastal sediments are major contributors to the production of atmospheric methane, the effects of environmental conditions on methanogenesis and the community of methanogenic archaea are not well understood. Here, we investigated the methanogenesis pathways in nearshore and offshore sediments from the South Yellow Sea (SYS). Moreover, the effects of the supply of methanogenic substrates (H₂/CO₂, acetate, trimethylamine (TMA), and methanol) and temperature on methanogenesis and the community of methanogenic archaea were further determined. Methylotrophic, hydrogenotrophic and acetotrophic methanogenesis were found to be responsible for biogenic methane production in nearshore sediments. In the offshore sediments, methylotrophic methanogenesis was the predominant methanogenic pathway. The changes in methanogenic community structure under different substrate amendments were characterized. Lower diversities were detected in substrate-amended samples with methanogenic activity. Hydrogenotrophic Methanogenium, multitrophic Methanosarcina, methylotrophic Methanococcoide, Methanococcoide or methylotrophic Methanolobus were dominant in H₂/CO₂-, acetate-, TMA- and methanol-amended sediment slurries, respectively. PCoA showed that the methanogen community in H₂/CO₂ and acetate amendments exhibited greater differences than those in other treatments. Lower temperature (10 °C) limits hydrogenotrophic and acetoclastic methanogenesis, but methylotrophic methanogenesis is much less affected. The response of methanogen diversity to the incubation temperature varied among the different substrate-amended slurries. The multitrophic methanogen Methanosarcina became increasingly abundant in H₂/CO_2- and acetate-amended sediment slurries when the temperature increased from 10 to 30 °C.

Anthropogenic and Environmental Constraints on the Microbial Methane Cycle in Coastal Sediments

Large amounts of methane, a potent greenhouse gas, are produced in anoxic sediments by methanogenic archaea. Nonetheless, over 90% of the produced methane is oxidized via sulfate-dependent anaerobic oxidation of methane (S-AOM) in the sulfate-methane transition zone (SMTZ) by consortia of anaerobic methane-oxidizing archaea (ANME) and sulfate-reducing bacteria (SRB). Coastal systems account for the majority of total marine methane emissions and typically have lower sulfate concentrations, hence S-AOM is less significant. However, alternative electron acceptors such as metal oxides or nitrate could be used for AOM instead of sulfate. The availability of electron acceptors is determined by the redox zonation in the sediment, which may vary due to changes in oxygen availability and the type and rate of organic matter inputs. Additionally, eutrophication and climate change can affect the microbiome, biogeochemical zonation, and methane cycling in coastal sediments. This review summarizes the current knowledge on the processes and microorganisms involved in methane cycling in coastal sediments and the factors influencing methane emissions from these systems. In eutrophic coastal areas, organic matter inputs are a key driver of bottom water hypoxia. Global warming can reduce the solubility of oxygen in surface waters, enhancing water column stratification, increasing primary production, and favoring methanogenesis. ANME are notoriously slow growers and may not be able to effectively oxidize methane upon rapid sedimentation and shoaling of the SMTZ. In such settings, ANME-2d (Methanoperedenaceae) and ANME-2a may couple iron- and/or manganese reduction to AOM, while ANME-2d and NC10 bacteria (Methylomirabilota) could couple AOM to nitrate or nitrite reduction. Ultimately, methane may be oxidized by aerobic methanotrophs in the upper millimeters of the sediment or in the water column. The role of these processes in mitigating methane emissions from eutrophic coastal sediments, including the exact pathways and microorganisms involved, are still underexplored, and factors controlling these processes are unclear. Further studies are needed in order to understand the factors driving methane-cycling pathways and to identify the responsible microorganisms. Integration of the knowledge on microbial pathways and geochemical processes is expected to lead to more accurate predictions of methane emissions from coastal zones in the future.

Gas ebullition from petroleum hydrocarbons in aquatic sediments: A review

Gas ebullition in sediment results from biogenic gas production by mixtures of bacteria and archaea. It often occurs in organic-rich sediments that have been impacted by petroleum hydrocarbon (PHC) and other anthropogenic pollution. Ebullition occurs under a relatively narrow set of biological, chemical, and sediment geomechanical conditions. This process occurs in three phases: I) biogenic production of primarily methane and dissolved phase transport of the gases in the pore water to a bubble nucleation site, II) bubble growth and sediment fracture, and III) bubble rise to the surface. The rate of biogenic gas production in phase I and the resistance of the sediment to gas fracture in phase II play the most significant roles in ebullition kinetics. What is less understood is the role that substrate structure plays in the rate of methanogenesis that drives gas ebullition. It is well established that methanogens have a very restricted set of compounds that can serve as substrates, so any complex organic molecule must first be broken down to fermentable compounds. Given that most ebullition-active sediments are completely anaerobic, the well-known difficulty in degrading PHCs under anaerobic conditions suggests potential limitations on PHC-derived gas ebullition. To date, there are no studies that conclusively demonstrate that weathered PHCs can alone drive gas ebullition. This review consists of an overview of the factors affecting gas ebullition and the biochemistry of anaerobic PHC biodegradation and methanogenesis in sediment systems. We next compile results from the scholarly literature on PHCs serving as a source of methanogenesis. We combine these results to assess the potential for PHC-driven gas ebullition using energetics, kinetics, and sediment geomechanics analyses. The results suggest that short chain <C₁₀ alkanes are the only PHC class that alone may have the potential to drive ebullition, and that PHC-derived methanogenesis likely plays a minor part in driving gas ebullition in contaminated sediments compared to natural organic matter.

Increasing sulfate levels show a differential impact on synthetic communities comprising different methanogens and a sulfate reducer

Methane-producing microbial communities are of ecological and biotechnological interest. Syntrophic interactions among sulfate reducers and aceto/hydrogenotrophic and obligate hydrogenotrophic methanogens form a key component of these communities, yet, the impact of these different syntrophic routes on methane production and their stability against sulfate availability are not well understood. Here, we construct model synthetic communities using a sulfate reducer and two types of methanogens representing different methanogenesis routes. We find that tri-cultures with both routes increase methane production by almost twofold compared to co-cultures and are stable in the absence of sulfate. With increasing sulfate, system stability and productivity decreases and does so faster in communities with aceto/hydrogenotrophic methanogens despite the continued presence of acetate. We show that this is due to a shift in the metabolism of these methanogens towards co-utilization of hydrogen with acetate. These findings indicate the important role of hydrogen dynamics in the stability and productivity of syntrophic communities.

Thermodynamic modelling of synthetic communities predicts minimum free energy requirements for sulfate reduction and methanogenesis

Microbial communities are complex dynamical systems harbouring many species interacting together to implement higher-level functions. Among these higher-level functions, conversion of organic matter into simpler building blocks by microbial communities underpins biogeochemical cycles and animal and plant nutrition, and is exploited in biotechnology. A prerequisite to predicting the dynamics and stability of community-mediated metabolic conversions is the development and calibration of appropriate mathematical models. Here, we present a generic, extendable thermodynamic model for community dynamics and calibrate a key parameter of this thermodynamic model, the minimum energy requirement associated with growth-supporting metabolic pathways, using experimental population dynamics data from synthetic communities composed of a sulfate reducer and two methanogens. Our findings show that accounting for thermodynamics is necessary in capturing the experimental population dynamics of these synthetic communities that feature relevant species using low energy growth pathways. Furthermore, they provide the first estimates for minimum energy requirements of methanogenesis (in the range of −30 kJ mol⁻¹) and elaborate on previous estimates of lactate fermentation by sulfate reducers (in the range of −30 to −17 kJ mol⁻¹ depending on the culture conditions). The open-source nature of the developed model and demonstration of its use for estimating a key thermodynamic parameter should facilitate further thermodynamic modelling of microbial communities.

Methane emission and sulfide levels increase in tropical seagrass sediments during temperature stress: A mesocosm experiment

Climate change-induced ocean warming is expected to greatly affect carbon dynamics and sequestration in vegetated shallow waters, especially in the upper subtidal where water temperatures may fluctuate considerably and can reach high levels at low tides. This might alter the greenhouse gas balance and significantly reduce the carbon sink potential of tropical seagrass meadows. In order to assess such consequences, we simulated temperature stress during low tide exposures by subjecting seagrass plants (Thalassia hemprichii) and associated sediments to elevated midday temperature spikes (31, 35, 37, 40, and 45°C) for seven consecutive days in an outdoor mesocosm setup. During the experiment, methane release from the sediment surface was estimated using gas chromatography. Sulfide concentration in the sediment pore water was determined spectrophotometrically, and the plant's photosynthetic capacity as electron transport rate (ETR), and maximum quantum yield (Fv/Fm) was assessed using pulse amplitude modulated (PAM) fluorometry. The highest temperature treatments (40 and 45°C) had a clear positive effect on methane emission and the level of sulfide in the sediment and, at the same time, clear negative effects on the photosynthetic performance of seagrass plants. The effects observed by temperature stress were immediate (within hours) and seen in all response variables, including ETR, Fv/Fm, methane emission, and sulfide levels. In addition, both the methane emission and the size of the sulfide pool were already negatively correlated with changes in the photosynthetic rate (ETR) during the first day, and with time, the correlations became stronger. These findings show that increased temperature will reduce primary productivity and increase methane and sulfide levels. Future increases in the frequency and severity of extreme temperature events could hence reduce the climate mitigation capacity of tropical seagrass meadows by reducing CO2 sequestration, increase damage from sulfide toxicity, and induce the release of larger amounts of methane.

Anaerobic co-digestion of chicken manure and microalgae Chlorella sp.: Methane potential, microbial diversity and synergistic impact evaluation

Anaerobic digestion (AD) is a promising alternative for livestock manure management. This paper presents the experimental results obtained through a batch experiment by using chicken manure (CM) and microalgae Chlorella sp. as co-substrates. The effect of co-digestion was evaluated by varying CM to Chlorella sp. ratios (0:10, 2:8, 4:6, 6:4, 8:2, 10: 0 based on the volatile solids (VS)). The major objective of this study is to evaluate the feasibility and synergistic impact of co-digestion of CM and Chlorella sp. Enhanced 14.20% and 76.86% methane production than CM and Chlorella sp. mono-digestion respectively was achieved in co-digestion at the ratio 8:2. In addition, the co-digestion at the ratio 8:2 showed significantly higher methane yield than the weighted average of the individual substrates' specific methane yield (WSMY), indicating strong synergy effect. The Illumina Miseq sequencing analysis showed that the AD process suppressed the acetoclastic methanogenesis Methanosaeta content; but partly enhanced hydrogenotrophic methanogenesis Methanosarcina, Methanospirillum and Methanobacterium, which was responsible for the methane production. The pre-treated microalgae was then introduced at the optimal ratio 8:2 to estimate the effect of pre-treatment of microalgae on AD process. However, the pre-treatment exhibited no positive effect.

Variations in Temperature Sensitivity (Q10) of CH4 Emission from a Subtropical Estuarine Marsh in Southeast China

Understanding the functional relationship between greenhouse gas fluxes and environmental variables is crucial for predicting the impacts of wetlands on future climate change in response to various perturbations. We examined the relationships between methane (CH₄) emission and temperature in two marsh stands dominated by the Phragmites australis and Cyperus malaccensis, respectively, in a subtropical estuarine wetland in southeast China based on three years of measurement data (2007–2009). We found that the Q₁₀ coefficient of CH₄ emission to soil temperature (Q_s10) from the two marsh stands varied slightly over the three years (P > 0.05), with a mean value of 3.38 ± 0.46 and 3.89 ± 0.41 for the P. australis and C. malaccensis stands, respectively. On the other hand, the three-year mean Q_a10 values (Q₁₀ coefficients of CH₄ emission to air temperature) were 3.39 ± 0.59 and 4.68 ± 1.10 for the P. australis and C. malaccensis stands, respectively, with a significantly higher Q_a10 value for the C. malaccensis stand in 2008 (P < 0.05). The seasonal variations of Q₁₀ (Q_s10 and Q_a10) differed among years, with generally higher values in the cold months than those in the warm months in 2007 and 2009. We found that the Q_s10 values of both stands were negatively correlated with soil conductivity, but did not obtain any conclusive results about the difference in Q₁₀ of CH₄ emission between the two tidal stages (before flooding and after ebbing). There were no significant differences in both Q_s10 and Q_a10 values of CH₄ emission between the P. australis stand and the C. malaccensis stands (P > 0.05). Our results show that the Q₁₀ values of CH₄ emission in this estuarine marsh are highly variable across space and time. Given that the overall CH₄ flux is governed by a suite of environmental factors, the Q₁₀ values derived from field measurements should only be considered as a semi-empirical parameter for simulating CH₄ emissions.

Microbial kinetic for In-Storage-Psychrophilic Anaerobic Digestion (ISPAD)

In-Storage-Psychrophilic-Anaerobic-Digestion (ISPAD) is a wastewater storage tank converted into an anaerobic digestion (AD) system by means of an airtight floating geo-membrane. For process optimization, ISPAD requires modelling with well-established microbial kinetics coefficients. The present objectives were to: obtain kinetics coefficients for the modelling of ISPAD; compare the prediction of the conventional and decomposition fitting approach, an innovative fitting technique used in other fields of science, and; obtain equations to predict the maximum growth rate (μmax) of microbial communities as a function of temperature. The method consisted in conducting specific Substrate Activity Tests (SAT) using ISPAD inoculum to monitor the rate of degradation of specific substrates at 8, 18 and 35 °C. Microbial kinetics coefficients were obtained by fitting the Monod equations to SAT. The statistical procedure of Least Square Error analysis was used to minimize the Sum of Squared Errors (SSE) between the measured ISPAD experimental data and the Monod equation values. Comparing both fitting methods, the decomposition approach gave higher correlation coefficient (R) for most kinetics values, as compared to the conventional approach. Tested to predict μmax with temperature, the Square Root equation better predicted temperature dependency of both acidogens and propionate degrading acetogens, while the Arrhenius equation better predicted that of methanogens and butyrate degrading acetogens. Increasing temperature from 18 to 35 °C did not affect butyrate degrading acetogens, likely because of their dominance, as demonstrated by microbial population estimation. The estimated ISPAD kinetics coefficients suggest a robust psychrophilic and mesophilic coexisting microbial community demonstrating acclimation to ambient temperature.

Effects of temperature and pH on the biokinetic properties of thiocyanate biodegradation under autotrophic conditions

The simultaneous effects of temperature and pH on the biokinetic properties of thiocyanate biodegradation under mixed-culture, autotrophic conditions were investigated using response surface analysis (RSA) combined with biokinetic modeling. A partial cubic model, based on substrate inhibition biokinetics, was constructed for each kinetic coefficient in Andrew model (i.e., maximum specific growth rate (μ(m)), saturation coefficient (K(S)), and substrate inhibition coefficient (K(SI))). Each model proved statistically reliable to approximate the responses of the kinetic coefficients to temperature and pH changes (r(2) > 0.8, p < 0.05). The response surface plots demonstrated that the biokinetic coefficients change with respect to temperature and pH significantly and in different ways. The model response surfaces were substantially different to each other, indicating distinct correlations between the independent (temperature and pH) and dependent (model response) variables in the models. Based on the estimated response surface models, temperature was shown to have significant effects on all biokinetic coefficients tested. A dominant influence of temperature on μ(m) response was observed while the interdependence of temperature and pH was apparent in the K(S) and K(SI) models. Specific growth rate (μ) versus substrate (i.e., thiocyanate) concentration plots simulating using the obtained response surface models confirmed the significant effects of temperature and pH on the microbial growth rate and therefore on the thiocyanate degradation rate. Overall, the response surface models able to describe the biokinetic effects of temperature and pH on thiocyanate biodegradation within the explored region (20-30 °C and pH 6.0-9.0) were successfully constructed and validated, providing fundamental information for better process control in thiocyanate treatment.

Searching for links in the biotic characteristics and abiotic parameters of nine different biogas plants

To find links between the biotic characteristics and abiotic process parameters in anaerobic digestion systems, the microbial communities of nine full‐scale biogas plants in South Tyrol (Italy) and Vorarlberg (Austria) were investigated using molecular techniques and the physical and chemical properties were monitored. DNA from sludge samples was subjected to microarray hybridization with the ANAEROCHIP microarray and results indicated that sludge samples grouped into two main clusters, dominated either by Methanosarcina or by Methanosaeta, both aceticlastic methanogens. Hydrogenotrophic methanogens were hardly detected or if detected, gave low hybridization signals. Results obtained using denaturing gradient gel electrophoresis (DGGE) supported the findings of microarray hybridization. Real‐time PCR targeting Methanosarcina and Methanosaeta was conducted to provide quantitative data on the dominating methanogens. Correlation analysis to determine any links between the microbial communities found by microarray analysis, and the physicochemical parameters investigated was conducted. It was shown that the sludge samples dominated by the genus Methanosarcina were positively correlated with higher concentrations of acetate, whereas sludge samples dominated by representatives of the genus Methanosaeta had lower acetate concentrations. No other correlations between biotic characteristics and abiotic parameters were found. Methanogenic communities in each reactor were highly stable and resilient over the whole year.

Hydrogen transfer between methanogens and fermentative heterotrophs in hyperthermophilic cocultures

Interactions involving hydrogen transfer were studied in a coculture of two hyperthermophilic microorganisms: Thermotoga maritima, an anaerobic heterotroph, and Methanococcus jannaschii, a hydrogenotrophic methanogen. Cell densities of T. maritima increased 10-fold when cocultured with M. jannaschii at 85 degrees C, and the methanogen was able to grow in the absence of externally supplied H(2) and CO(2). The coculture could not be established if the two organisms were physically separated by a dialysis membrane, suggesting the importance of spatial proximity. The significance of spatial proximity was also supported by cell cytometry, where the methanogen was only found in cell sorts at or above 4.5 microm in samples of the coculture in exponential phase. An unstructured mathematical model was used to compare the influence of hydrogen transport and metabolic properties on mesophilic and hyperthermophilic cocultures. Calculations suggest the increases in methanogenesis rates with temperature result from greater interactions between the methanogenic and fermentative organisms, as evidenced by the sharp decline in H(2) concentration in the proximity of a hyperthermophilic methanogen. The experimental and modeling results presented here illustrate the need to consider the interactions within hyperthermophilic consortia when choosing isolation strategies and evaluating biotransformations at elevated temperatures.

Ecological control analysis: being(s) in control of mass flux and metabolite concentrations in anaerobic degradation processes

Identification of the functional groups of microorganisms that are predominantly in control of fluxes through, and concentrations in, microbial networks would benefit microbial ecology and environmental biotechnology: the properties of those controlling microorganisms could be studied or monitored specifically or their activity could be modulated in attempts to manipulate the behaviour of such networks. Herein we present ecological control analysis (ECA) as a versatile mathematical framework that allows for the quantification of the control of each functional group in a microbial network on its process rates and concentrations of intermediates. In contrast to current views, we show that rates of flow of matter are not always limited by a single functional group; rather flux control can be distributed over several groups. Also, control over intermediate concentrations is always shared. Because of indirect interactions, through other functional groups, the concentration of an intermediate can also be controlled by functional groups not producing or consuming it. Ecological control analysis is illustrated by a case study on the anaerobic degradation of organic matter, using experimental data obtained from the literature. During anaerobic degradation, fermenting microorganisms interact with terminal electron-accepting microorganisms (e.g. halorespirers, methanogens). The analysis indicates that flux control mainly resides with fermenting microorganisms, but can shift to the terminal electron-accepting microorganisms under less favourable redox conditions. Paradoxically, halorespiring microorganisms do not control the rate of perchloroethylene and trichloroethylene degradation even though they catalyse those processes themselves.

Anaerobic and complementary treatment of domestic sewage in regions with hot climates--a review

This study presents a literature review on the treatment of domestic sewage in controlled environments having the anaerobic process and specifically the upflow anaerobic sludge blanket (UASB) concept as the core, under natural hot conditions. The UASB process application is however beset by the preponderance of suspended solids, and the paper looks at its optimization via pre- and post-treatments to curb the prevailing problems, in the light of possible discharge and re-use/recycling/resource recovery, leading to efficient environmental protection. Pre-treatment clarification could be done with ferric chloride/polyelectrolyte, so that phosphate precipitates during the process. The pre-treated liquid phase can be submitted to a high rate anaerobic process, using the simple and robust UASB technology. In a subsequent post-treatment step, ammonium can be removed by ion exchange using a zeolite column through which the wastewater percolates after leaving the anaerobic digester. The various stages can also eliminate a large fraction of the pathogens present in the raw wastewater, mainly through the pre-treatment sedimentation and the ion exchange filtration. The sludge produced in the precipitation stage can be stabilized in a conventional anaerobic digester. Integration of the different treatment steps provides a sustainable technology to treat domestic sewage under hot climate conditions.

Comparison of pulsed and continuous addition of H2 gas via membranes for stimulating PCE biodegradation in soil columns

Column experiments were performed to investigate a technology for remediating aquifers contaminated with chlorinated solvents. The technology involves installation of hollow-fiber membranes in the subsurface to supply hydrogen gas (H2) to groundwater to support biological reductive dechlorination in situ. Three laboratory-scale columns [control (N2 only), continuous H2, and pulsed H2] were packed with aquifer material from a trichloroethene (TCE)-contaminated wetland in Minnesota and supplied with perchloroethene (PCE)-contaminated synthetic groundwater. The main goals of the research were: (1) evaluate the long-term performance of the H2 supply system and (2) compare the effects of pulsed (4 h on, 20 h off) versus continuous H2 supply (lumen partial pressure approximately 1.2 atm) on PCE dechlorination and production of by-products (i.e. methane and acetate). The silicone-coated fiberglass membranes employed in these experiments were robust, delivering H2 steadily over the entire 349-day experiment. Methane production decreased when H2 was added in a pulsed manner. Nevertheless, the percentage of added H2 used to support methanogenesis was similar in both H2-fed columns (92-93%). For much of the experiment, PCE dechlorination (observed end product = dichloroethene) in the continuous and pulsed H2 columns was comparable, and enhanced in comparison to the natural attenuation observed in the control column. Dechlorination began to decline in the pulsed H2 column after 210 days, however, while dechlorination in the continuous H2 column was sustained. Acetate was detected only in the continuous H2 column, at concentrations of up to 36 microM. The results of this research suggest that in situ stimulation of PCE dechlorination by direct H2 addition requires the continuous application of H2 at high partial pressures, favoring the production of bioavailable organic matter such as acetate to provide a carbon source, electron donor, or both for dechlorinators. Unfortunately, this strategy has proven to be inefficient, with the bulk of the added H2 used to support methanogenesis.

Acidogenesis of gelatin-rich wastewater in an upflow anaerobic reactor: influence of pH and temperature

The influence of temperature and pH on the acidification of a synthetic gelatin based wastewater was investigated using an upflow anaerobic reactor. Gelatin degradation efficiency and rate, degree of acidification, and formation rate of volatile fatty acids and alcohols all slightly increased with temperature. Temperature affected the acidogenesis of gelatin according to the Arrhenius equation with an activation energy of 1.83 kcal/mol. Compared with temperature, pH had a more significant effect on the acidogenesis. Gelatin degradation efficiency substantially increased with pH, from 60.0% at pH 4.0 to 97.5% at pH 7.0. The degree of acidification increased from 32.0% at pH 4.0 to 71.6% at pH 6.5, but dropped to 66.8% when pH increased to 7.0. The optimum pH for the overall acidogenic activity was found to be 6.0, close to 5.9, the optimum pH calculated using a semi-empirical model. Operation at pH of 4.0-5.0 favored the production of propionate, hydrogen, whereas the operation at pH 6.0-7.0 encouraged the production of acetate, butyrate, and i-butyrate. The region between pH 5.0 and 6.0 was the transition zone.

Evaluation of kinetic coefficients using integrated monod and haldane models for low-temperature acetoclastic methanogenesis

The integrated Monod and Haldane models were used to evaluate the kinetic coefficients and their standard deviations using the methane accumulation curves of low-temperature acetoclastic methanogenesis. The linear and exponential approximations and the limitations of their applicability were deduced from the integrated models. The samples of lake sediments and biomass taken from a low-temperature upflow anaerobic sludge blanket (UASB) reactor were used as inoculum in batch assays for acetate methanation. In comparison, the Monod and Haldane models were applied to evaluate the kinetic coefficients for mesophilic acetoclastic methanogenesis accomplished by the pure culture of Methanosarcina barkeri strain MS. The Monod and Haldane models and their approximations were fitted by using non-linear regression. For the wide range of initial acetateconcentrations (4.2-84 mM: 5-100 mM) applied to the UASB biomass at 11 and 22 degrees C and for the lake sediment samples at 6 and 15 degrees C, a better fit was obtained with the Haldane models and their exponential approximations, respectively. For the lake sediments the values of inhibition coefficients decreased at decreasing temperatures. At the highest temperature of 30 degrees C no difference was found between the Haldane and Monod models and the simpler Monod model should be preferred. The values of the maximum growth rate of biomass were highest at 30 degrees C (lake sediment) and 22 degrees C (the UASB biomass) being in a range presented in the literature for mesophilic acetoclastic methanogenesis.

Effect of temperature on carbon and electron flow and on the archaeal community in methanogenic rice field soil

Temperature is an important factor controlling CH(4) production in anoxic rice soils. Soil slurries, prepared from Italian rice field soil, were incubated anaerobically in the dark at six temperatures of between 10 to 37 degrees C or in a temperature gradient block covering the same temperature range at intervals of 1 degrees C. Methane production reached quasi-steady state after 60 to 90 days. Steady-state CH(4) production rates increased with temperature, with an apparent activation energy of 61 kJ mol(-1). Steady-state partial pressures of the methanogenic precursor H(2) also increased with increasing temperature from <0.5 to 3.5 Pa, so that the Gibbs free energy change of H(2) plus CO(2)-dependent methanogenesis was kept at -20 to -25 kJ mol of CH(4)(-1) over the whole temperature range. Steady-state concentrations of the methanogenic precursor acetate, on the other hand, increased with decreasing temperature from <5 to 50 microM. Simultaneously, the relative contribution of H(2) as methanogenic precursor decreased, as determined by the conversion of radioactive bicarbonate to (14)CH(4), so that the carbon and electron flow to CH(4) was increasingly dominated by acetate, indicating that psychrotolerant homoacetogenesis was important. The relative composition of the archaeal community was determined by terminal restriction fragment length polymorphism (T-RFLP) analysis of the 16S rRNA genes (16S rDNA). T-RFLP analysis differentiated the archaeal Methanobacteriaceae, Methanomicrobiaceae, Methanosaetaceae, Methanosarcinaceae, and Rice clusters I, III, IV, V, and VI, which were all present in the rice field soil incubated at different temperatures. The 16S rRNA genes of Rice cluster I and Methanosaetaceae were the most frequent methanogenic groups. The relative abundance of Rice cluster I decreased with temperature. The substrates used by this microbial cluster, and thus its function in the microbial community, are unknown. The relative abundance of acetoclastic methanogens, on the other hand, was consistent with their physiology and the acetate concentrations observed at the different temperatures, i.e., the high-acetate-requiring Methanosarcinaceae decreased and the more modest Methanosaetaceae increased with increasing temperature. Our results demonstrate that temperature not only affected the activity but also changed the structure and the function (carbon and electron flow) of a complex methanogenic system.

Structure and function of the methanogenic archaeal community in stable cellulose-degrading enrichment cultures at two different temperatures (15 and 30 degrees C)

Methanogenic cultures were enriched from an air-dried rice field soil and incubated under anaerobic conditions at 30 degrees C with cellulose as substrate (ET1). The culture was then transferred and further incubated at either 15 degrees C (E15) or 30 degrees C (E30), to establish stable cultures that methanogenically degrade cellulose. After five transfers, the rates of CH(4) production became reproducible. At 30 degrees C, CH(4) production rates were (mean+/-S.D.) 15.2+/-0.7 nmol h(-1) ml(-1) culture for the next 16 transfers and at 15 degrees C, they were 0.38+/-0.07 nmol h(-1) ml(-1) for the next six transfers. When E30 was assayed at temperatures between 5-50 degrees C, CH(4) production rates increased with the temperature, reached a maximum at 40 degrees C and then decreased. The same temperature optimum was observed in E15, but with a lower maximum CH(4) production rate. The apparent activation energies of CH(4) production were similar (about 120 kJ mol(-1)4 mM at the beginning of the assay. The structure of the archaeal community was analyzed by molecular techniques. Total DNA was extracted from the microbial cultures before the transfer to different temperatures (ET1) and afterwards (E15, E30). The archaeal small subunit (SSU) ribosomal RNA-encoding genes (rDNA) of these DNA samples were amplified by PCR with archaeal-specific primers and characterized by terminal restriction fragment length polymorphism (T-RFLP). After obtaining a constant T-RFLP pattern in the cultural transfers at 15 and 30 degrees C, the PCR amplicons were used for the generation of clone libraries. Representative rDNA clones (n=10 for each type of culture) were characterized by T-RFLP and sequence analysis. In the primary culture (ET1), the archaeal community was dominated by clones representing 'rice cluster I', a novel lineage of methanogenic Euryarchaeota. However, further transfers resulted in the dominance of Methanosarcinaceae and Methanosaetaceae at 30 and 15 degrees C, respectively. This dominance was confirmed by fluorescence in situ hybridization (FISH) of archaeal cells. Obviously, different archaeal communities were established at the two different temperatures, but their activities nevertheless exhibited similar temperature optima.

Effect of temperature on sulphate reduction, growth rate and growth yield in five psychrophilic sulphate-reducing bacteria from Arctic sediments

Five psychrophilic sulphate-reducing bacteria (strains ASv26, LSv21, PSv29, LSv54 and LSv514) isolated from Arctic sediments were examined for their adaptation to permanently low temperatures. All strains grew at -1.8 degrees C, the freezing point of sea water, but their optimum temperature for growth (T(opt)) were 7 degrees C (PSv29), 10 degrees C (ASv26, LSv54) and 18 degrees C (LSv21, LSv514). Although T(opt) was considerably above the in situ temperatures of their habitats (-1.7 degrees C and 2.6 degrees C), relative growth rates were still high at 0 degrees C, accounting for 25-41% of those at T(opt). Short-term incubations of exponentially growing cultures showed that the highest sulphate reduction rates occurred 2-9 degrees C above T(opt). In contrast to growth and sulphate reduction rates, growth yields of strains ASv26, LSv54 and PSv29 were almost constant between -1.8 degrees C and T(opt). For strains LSv21 and LSv514, however, growth yields were highest at the lowest temperatures, around 0 degrees C. The results indicate that psychrophilic sulphate-reducing bacteria are specially adapted to permanently low temperatures by high relative growth rates and high growth yields at in situ conditions.

Microbial phenol degradation of organic compounds in natural systems: Temperature-inhibition relationships

The combined influence of high phenol concentrations and low temperatures on aerobic and anaerobic phenol degradation kinetics was investigated in microbial enrichment cultures to evaluate temperature-inhibition relationships with respect to the ambient conditions in polluted habitats. The inhibition of microbial phenol degradation by excess substrate was found to be temperature-dependent. Substrate inhibition was intensified when temperatures were lower. This results in an elevated temperature sensitivity of phenol degradation at inhibitory substrate concentrations. The synergistic amplification of substrate inhibition at low temperatures may help to explain the limited self-purification potential of contaminated habitats such as soils, sediments and groundwater aquifers where high pollutant concentrations and low temperatures prevail.

Temperature-dependent growth kinetics of Escherichia coli ML 30 in glucose-limited continuous culture

Detailed comparison of growth kinetics at temperatures below and above the optimal temperature was carried out with Escherichia coli ML 30 (DSM 1329) in continuous culture. The culture was grown with glucose as the sole limiting source of carbon and energy (100 mg liter(-1) in feed medium), and the resulting steady-state concentrations of glucose were measured as a function of the dilution rate at 17.4, 28.4, 37, and 40 degrees C. The experimental data could not be described by the conventional Monod equation over the entire temperature range, but an extended form of the Monod model [mu = mu(max) x (s - s(min))/(Ks + s - s(min))], which predicts a finite substrate concentration at 0 growth rate (s(min)), provided a good fit. The two parameters mu(max) and s(min) were temperature dependent, whereas, surprisingly, fitting the model to the experimental data yielded virtually identical Ks values (approximately 33 microg liter(-1)) at all temperatures. A model that describes steady-state glucose concentrations as a function of temperature at constant growth rates is presented. In similar experiments with mixtures of glucose and galactose (1:1 mixture), the two sugars were utilized simultaneously at all temperatures examined, and their steady-state concentrations were reduced compared with to growth with either glucose or galactose alone. The results of laboratory-scale kinetic experiments are discussed with respect to the concentrations observed in natural environments.

Effects of hydrogen and formate on the degradation of propionate and butyrate in thermophilic granules from an upflow anaerobic sludge blanket reactor

Degradation of propionate and butyrate in whole and disintegrated granules from a thermophilic (55 degrees C) upflow anaerobic sludge blanket reactor fed with acetate, propionate, and butyrate as substrates was examined. The propionate and butyrate degradation rates in whole granules were 1.16 and 4.0 mumol/min/g of volatile solids, respectively, and the rates decreased 35 and 25%, respectively, after disintegration of the granules. The effect of adding different hydrogen-oxidizing bacteria (both sulfate reducers and methanogens), some of which used formate in addition to hydrogen, to disintegrated granules was tested. Addition of either Methanobacterium thermoautotrophicum delta H, a hydrogen-utilizing methanogen that does not use formate, or Methanobacterium sp. strain CB12, a hydrogen- and formate-utilizing methanogen, to disintegrated granules increased the degradation rate of both propionate and butyrate. Furthermore, addition of a thermophilic sulfate-reducing bacterium (a Desulfotomaculum sp. isolated in our laboratory) to disintegrated granules improved the degradation of both substrates even more than the addition of methanogens. By monitoring the hydrogen partial pressure in the cultures, a correlation between the hydrogen partial pressure and the degradation rate of propionate and butyrate was observed, showing a decrease in the degradation rate with increased hydrogen partial pressure. No significant differences in the stimulation of the degradation rates were observed when the disintegrated granules were supplied with methanogens that utilized hydrogen only or hydrogen and formate. This indicated that interspecies formate transfer was not important for stimulation of propionate and butyrate degradation.