Methanogenic Organisms Research Articles

Numerical modelling of the transport of trace gases including methane in the subsurface of Mars

We model the transport of gas through the martian subsurface in order to quantify the timescales of release of a trace gas with a source at depth using a Fickian model of diffusion through a putative martian regolith column. The model is then applied to the case of methane to determine if diffusive transport of gas can explain previous observations of methane in the martian atmosphere.We investigate which parameters in the model have the greatest effect on transport timescales and show that the calculated diffusivity is very sensitive to the pressure profile of the subsurface, but relatively insensitive to the temperature profile, though diffusive transport may be affected by other temperature dependent properties of the subsurface such as the local vapour pressure. Uncertainties in the structure and physical conditions of the martian subsurface also introduce uncertainties in the timescales calculated.It was found that methane may take several hundred thousand Mars-years to diffuse from a source at depth. Purely diffusive transport cannot explain transient release that varies on timescales of less than one martian year from sources such as serpentinization or methanogenic organisms at depths of more than 2km. However, diffusion of gas released by the destabilisation of methane clathrate hydrates close to the surface, for example caused by transient mass wasting events or erosion, could produce a rapidly varying flux of methane into the atmosphere of more than 10−3kgm−2s−1 over a duration of less than half a martian year, consistent with observations of martian methane variability. Seismic events, magmatic intrusions or impacts could also potentially produce similar patterns of release, but are far more complex to simulate.

Climate Change and Global Warming Is Produced by Human Endosymbiotic Archaeal Overgrowth and Methanogenesis

Climate Change and Global Warming Is Produced by Human Endosymbiotic Archaeal Overgrowth and Methanogenesis

Investigation into the effect of high concentrations of volatile fatty acids in anaerobic digestion on methanogenic communities

A study was conducted to determine whether differences in the levels of volatile fatty acids (VFAs) in anaerobic digester plants could result in variations in the indigenous methanogenic communities. Two digesters (one operated under mesophilic conditions, the other under thermophilic conditions) were monitored, and sampled at points where VFA levels were high, as well as when VFA levels were low. Physical and chemical parameters were measured, and the methanogenic diversity was screened using the phylogenetic microarray ANAEROCHIP. In addition, real-time PCR was used to quantify the presence of the different methanogenic genera in the sludge samples. Array results indicated that the archaeal communities in the different reactors were stable, and that changes in the VFA levels of the anaerobic digesters did not greatly alter the dominating methanogenic organisms. In contrast, the two digesters were found to harbour different dominating methanogenic communities, which appeared to remain stable over time. Real-time PCR results were inline with those of microarray analysis indicating only minimal changes in methanogen numbers during periods of high VFAs, however, revealed a greater diversity in methanogens than found with the array.

Eremophila glabra reduces methane production and methanogen populations when fermented in a Rusitec

Eremophila glabra Juss. (Scrophulariaceae), a native Australian shrub, has been demonstrated to have low methanogenic potential in a batch in vitro fermentation system. The present study aimed to test longer-term effects of E. glabra on rumen fermentation characteristics, particularly methane production and the methanogen population, when included as a component of a fermentation substrate in an in vitro continuous culture system (Rusitec). E. glabra was included at 150, 250, 400 g/kg DM (EG15, EG25, and EG40) with an oaten chaff and lupin-based substrate (control). Overall, the experiment lasted 33 days, with 12 days of acclimatization, followed by two periods during which fermentation characteristics (total gas, methane and VFA productions, dry matter disappearance, pH) were measured. The number of copies of genes specifically associated with total bacteria and cellulolytic bacteria (16S rRNA gene) and total ruminal methanogenic archaeal organisms (the methyl coenzyme M reductase A gene (mcrA)) was also measured during this time using quantitative real-time PCR. Total gas production, methane and volatile fatty acid concentrations were significantly reduced with addition of E. glabra. At the end of the experiment, the overall methane reduction was 32% and 45% for EG15 and EG25 respectively, compared to the control, and the reduction was in a dose-dependent manner. Total bacterial numbers did not change, but the total methanogen population decreased by up to 42.1% (EG40) when compared to the control substrate. The Fibrobacter succinogenes population was reduced at all levels of E. glabra, while Ruminococcus albus was reduced only by EG40. Our results indicate that replacing a portion of a fibrous substrate with E. glabra maintained a significant reduction in methane production and methanogen populations over three weeks in vitro, with some minor inhibition on overall fermentation at the lower inclusion levels.

Methanoculleus horonobensis sp. nov., a methanogenic archaeon isolated from a deep diatomaceous shale formation

A methanogenic organism from the domain Archaea, designated strain T10(T), was isolated from groundwater sampled from a deep diatomaceous shale formation located in Horonobe, Hokkaido, Japan. The strain utilized H2/CO2 and formate as substrates for methanogenesis. Cells were strictly anaerobic, Gram-negative-staining, flagellated, irregular coccoids, 0.7-1.6 µm in diameter, and occurred singly. The strain grew at 25-45 °C (optimum 37-42 °C), at pH 5.8-8.2 (optimum pH 6.7-6.8) and in the presence of 0-1.3 M NaCl (optimum 0.1-0.2 M NaCl). The G+C content of the genomic DNA was 62.9 mol%. 16S rRNA gene sequencing revealed that, although the strain is a member of the genus Methanoculleus, it clearly differed from all described species of this genus (95.5-98.3 % sequence similarity). Values for DNA-DNA hybridization with type strains of closely related Methanoculleus species were less than 50 %. Phenotypic and phylogenetic features of strain T10(T) clearly indicate that it represents a novel species of the genus Methanoculleus, for which the name Methanoculleus horonobensis sp. nov. is proposed. The type strain is T10(T) ( = DSM 21626(T) = JCM 15517(T)).

Metagenome and metaproteome analyses of microbial communities in mesophilic biogas-producing anaerobic batch fermentations indicate concerted plant carbohydrate degradation

Microbial communities in biogas batch fermentations, using straw and hay as co-substrates, were analyzed at the gene and protein level by metagenomic and metaproteomic approaches. The analysis of metagenomic data revealed that the Clostridiales and Bacteroidales orders were prevalent in the community. However, the number of sequences assigned to the Clostridiales order decreased during fermentation, whereas the number of sequences assigned to the Bacteroidales order increased. In addition, changes at the functional level were monitored and the metaproteomic analyses detected transporter proteins and flagellins, which were expressed mainly by members of the Bacteroidetes and Firmicutes phyla. A high number of sugar transporters, expressed by members of the Bacteroidetes, proved their potential to take up various glycans efficiently. Metagenome data also showed that methanogenic organisms represented less than 4% of the community, while 20–30% of the identified proteins were of archeal origin. These data suggested that methanogens were disproportionally active.In conclusion, the community studied was capable of digesting the recalcitrant co-substrate. Members of the Firmicutes phylum seemed to be the main degraders of cellulose, even though expression of only a few glycoside hydrolases was detected. The Bacteroidetes phylum expressed a high number of sugar transporters and seemed to specialize in the digestion of other polysaccharides. Finally, it was found that key enzymes of methanogenesis were expressed in high quantities, indicating the high metabolic activity of methanogens, although they only represented a minor group within the microbial community.

Impact of protein-, lipid- and cellulose-containing complex substrates on biogas production and microbial communities in batch experiments

In the present study, nine complex organic substrates from three classes (protein-, lipid-, and cellulose-rich) were investigated in batch experiments and compared with a control in order to evaluate their potential for utilisation as substrates for biogas production. High methane production was observed from protein-rich substrates; problems arose from lipid-containing, lactose and cellulose fermentation. Using DGGE analysis it could be shown that different classes of substrate resulted in different microbial communities, whereupon similar substrates tended to show a similar microbial structure. By means of qPCR Methanoculleus sp., a hydrogenotrophic methanogen was found to be the most abundant organism in the batch experiments. Additionally, it could be demonstrated that methanogenic organisms withstood adverse environmental conditions for at least an incubation period of 55days, pointing to a high stability of the archaeal community even in times of decreasing or even failing fermenter performance.

A proteomic view at the biochemistry of syntrophic butyrate oxidation in Syntrophomonas wolfei.

In syntrophic conversion of butyrate to methane and CO2, butyrate is oxidized to acetate by secondary fermenting bacteria such as Syntrophomonas wolfei in close cooperation with methanogenic partner organisms, e.g., Methanospirillum hungatei. This process involves an energetically unfavourable shift of electrons from the level of butyryl-CoA oxidation to the substantially lower redox potential of proton and/or CO2 reduction, in order to transfer these electrons to the methanogenic partner via hydrogen and/or formate.In the present study, all prominent membrane-bound and soluble proteins expressed in S. wolfei specifically during syntrophic growth with butyrate, in comparison to pure-culture growth with crotonate, were examined by one- and two-dimensional gel electrophoresis, and identified by peptide fingerprinting-mass spectrometry. A membrane-bound, externally oriented, quinone-linked formate dehydrogenase complex was expressed at high level specifically during syntrophic butyrate oxidation, comprising a selenocystein-linked catalytic subunit with a membrane-translocation pathway signal (TAT), a membrane-bound iron-sulfur subunit, and a membrane-bound cytochrome. Soluble hydrogenases were expressed at high levels specifically during growth with crotonate. The results were confirmed by native protein gel electrophoresis, by formate dehydrogenase and hydrogenase-activity staining, and by analysis of formate dehydrogenase and hydrogenase activities in intact cells and cell extracts. Furthermore, constitutive expression of a membrane-bound, internally oriented iron-sulfur oxidoreductase (DUF224) was confirmed, together with expression of soluble electron-transfer flavoproteins (EtfAB) and two previously identified butyryl-CoA dehydrogenases.Our findings allow to depict an electron flow scheme for syntrophic butyrate oxidation in S. wolfei. Electrons derived from butyryl-CoA are transferred through a membrane-bound EtfAB:quinone oxidoreductase (DUF224) to a menaquinone cycle and further via a b-type cytochrome to an externally oriented formate dehydrogenase. Hence, an ATP hydrolysis-driven proton-motive force across the cytoplasmatic membrane would provide the energy input for the electron potential shift necessary for formate formation.

Lower operational limits to volatile fatty acid degradation with dilute wastewaters in an anaerobic fluidized bed reactor

A general concern that anaerobic treatment of dilute wastewaters is limited by the inability of methanogenic and related syntrophic organisms to reduce substrate concentrations adequately was evaluated using a 35°C granular activated carbon-containing laboratory-scale fluidized bed reactor fed an acetate-propionate equal chemical oxygen demand (COD) mixture synthetic wastewater. Contrary to general expectations, effluent acetate and propionate concentrations remained near or below their detection limits of 0.4mg COD/L with influent COD of 200mg/L, 17min hydraulic retention time, and organic loading as high as 17kg COD/m3d, or with influent COD values ranging from 45 to 2010mg COD/L and organic loadings of 4.2–4.5kg COD/m3d. The effluent acetate concentrations in these well-fed systems were at or much below reported threshold limits for starving non-fed cultures, suggesting that a better understanding of threshold values and factors affecting treatment efficiency with anaerobic treatment of dilute wastewaters is needed.

Spatial and temporal changes in microbial diversity of the Marmara Sea Sediments

Spatial (10 different locations) and temporal (2years) changes in characteristics of the Marmara Sea Sediments were monitored to determine interactions between the chemical and microbial diversity. The sediments were rich in terms of hydrocarbon, nitrate, Ni and microbial cell content. Denitrifying, sulfate reducing, fermentative and methanogenic organisms were co-abundant in 15cm below the sea floor. The local variations in the sediments’ characteristics were more distinctive than the temporal ones. The sulfate and nitrate contents were the main drivers of the changes in the microbial community compositions. N and P were limited for microbial growth in the sediments, and their levels determined the total cell abundance and activity. Seasonal shifts in temperatures of the shallow sediments were also reflected in the active cell abundances. It was concluded that the Marmara Sea is a promising ecosystem for the further investigation of the ecologically important microbial processes.

Coping with the Environment: How Microbes Survive Environmental Challenges

Microorganisms are exposed to constantly changing environments in their natural habitats either in planktonic form or microbial communities. Examples of these environmental changes encompass nutrient limitation, temperature, pH, and osmolarity fluctuations, radiation, and other harmful agents, such as excessive amount of superoxides and heavy metals. To respond and adapt to adverse environmental changes, microorganisms employ a striking combination of transcriptional regulatory circuits to sense and translate extracellular stimuli into specific cellular signals, resulting in altered gene expression and protein activities. Investigation of these underlying mechanisms and strategies could improve our understanding of microbial physiology in general and potentially lead to discoveries of practical value in the field of health care and environment protection. In this special issue, we have invited a few papers that explore this topic from various perspectives. The first paper “Exposure to glycolytic carbon sources reveals a novel layer of regulation for the MalT regulon” presents the study on a synthetic lethal mutant ompR malTcon of Escherichia coli in which the constitutively expressed maltose system regulator MalT in its active form causes cell death in the absence of the osmoregulator OmpR. The authors propose that glycolysis provides a new layer of regulation to the maltose system on the basis that addition of glycolytic carbon sources promotes viability of the mutant. The second paper “The effect of sub-MIC β-lactam antibiotic exposure of Pseudomonas aeruginosa strains from people with cystic fibrosis in a desiccation survival model” examines resistance of Pseudomonas aeruginosa strains to desiccation, which is an important environmental factor to the loss of viability of cells. Strains with a mucoid phenotype exhibit significantly improved desiccation survival when compared with nonmucoid ones, but effects of preincubation with sub-MIC beta-lactam antibiotics on desiccation resistance appear to be agent specific. The third paper “Detection of bacterial endospores in soil by terbium fluorescence” of this special issue addresses the relationship of soil parameters (carbon-to-nitrogen ratio) on the occurrence of bacterial spores and distribution of spores in relation to sampling depth. The results demonstrate that the combination of microwave treatment of soil samples and measurement of terbium dipicolinate (DPA) photoluminescence is a rapid and reliable method for the assessment of bacterial spores. The fourth paper “The sulfate-rich and extreme saline sediment of the ephemeral Tirez lagoon: a biotope for acetoclastic sulfate-reducing bacteria and hydrogenotrophic methanogenic archaea” is on the composition of methanogenic archaea, sulfate-reducing and sulfur-oxidizing prokaryotes in the extreme athalassohaline and particularly sulfate-rich sediment of Tirez Lagoon. The occurrence of hydrogenotrophic methanogenic and acetotrophic sulfate-reducing organisms and winter-summer community structures in Tirez sediment are analyzed by using the PCR-DGGE fingerprint technique for the functional adenosine-5′-phosphosulfate (aprA) and the methyl coenzyme M reductase (mcrA) gene markers. The last paper “Stress responses of Shewanella” of this special issue focuses on stress responses of Shewanella, a group of facultative anaerobes capable of respiring on an array of compounds. As important and potential microorganisms for bioremediation, stress responses of Shewanella have been subjected to an array of analyses, especially with high-throughput technologies such as whole-genome microarrays. This comprehensive review highlights the current understanding of mechanisms by which Shewanella survive and thrive within varied environments, as well as points out promising future research directions. Haichun Gao Tao Weitao Qiang He

Anaerobic Digestion of Domestic Wastewater: The Role of Alkalinity in the Rate and Extent of Digestion

For an anaerobic baffled reactor (ABR) treating domestic wastewater, the major variables affecting the rate and extent of digestion are the organic loading/residence time, the upflow velocity and the pH/alkalinity characteristics of the wastewater. In this study, an ABR was operated at two different flow rates; in Phase A, a higher loading rate of 0.74 kgCOD/m3.d was employed, while in Phase B, the loading rate was reduced to 0.40 kgCOD/m3.d. At the higher organic loading rate, significantly higher solids accumulation rates per kgCOD treated were obtained, and it was estimated that only 30% of the influent COD was converted to CH4. At the lower loading rate the estimated conversion to methane was 60%. The most probable cause for the poor COD removal was failure of stable anaerobic microbial consortia to establish under the relatively high selection pressure experienced at the high loading rate, due to washout of anaerobic species. It was concluded that low wastewater alkalinity (240 mgCaCO3/l) characteristic of the KwaZulu-Natal East Coast region resulted in low compartment pH values and associated inhibition of microbial activity, causing slower digestion of organics, and greater washout, particularly of methanogenic organisms, at higher up-flow velocities. The implication was that critical value for up-flow velocity, above which washout of anaerobic species occurs, depends on the organic loading and the prevailing pH and alkalinity. This has implications for the stability of any anaerobic system, and the extent of treatment of the effluent, specifically, that low wastewater alkalinity has the potential to significantly affect reactor design in any anaerobic system.

Methanosarcina horonobensis sp. nov., a methanogenic archaeon isolated from a deep subsurface Miocene formation

A methanogenic organism, designated strain HB-1(T), from the domain Archaea was isolated from groundwater sampled from a subsurface Miocene formation located in Horonobe, Hokkaido, Japan. The strain grew on methanol, dimethylamine, trimethylamine, dimethylsulfide and acetate but not on monomethylamine, H(2)/CO(2), formate, 2-propanol, 2-butanol or cyclopentanol. Cells were Gram-reaction-negative, non-motile, irregular cocci that were 1.4-2.9 µm in diameter and occurred singly or in pairs. The strain grew at 20-42 °C (optimum 37 °C), at pH 6.0-7.75 (optimum pH 7.0-7.25) and in 0-0.35 M NaCl (optimum 0.1 M). The G+C content of the genomic DNA was 41.4 mol%. 16S rRNA gene sequencing revealed that the strain was a member of the genus Methanosarcina but that it clearly differed from all recognized species of this genus (93.1-97.9 % sequence similarity). The phenotypic and phylogenetic features of strain HB-1(T) indicate that it represents a novel species of the genus Methanosarcina, for which the name Methanosarcina horonobensis sp. nov. is proposed. The type strain is HB-1(T) ( = DSM 21571(T) = JCM 15518(T) = NBRC 102577(T)).

Wastewater transformations and fertilizer value when co-digesting differing ratios of swine manure and used cooking grease in low-cost digesters

A nine-month co-digestion investigation was conducted in Costa Rica to optimize animal wastewater treatment, renewable energy production, and fertilizer creation using 12 Taiwanese-model, plug-flow digesters (250 L each) constructed of tubular polyethylene and PVC piping, operating without mechanical or heating components. The experiment tested three replications of four treatment groups: the control (T0), which contained only swine manure, and T2.5, T5, and T10, which contained 2.5%, 5%, and 10% used cooking grease (by volume) combined with swine manure. T2.5 had the greatest methane production (45 L d −1), a 124% increase from the control. No adverse effects were observed from co-digesting 2.5% grease in terms of organic matter removal, pathogen reduction, grease removal, and pH. Chemical oxygen demand (COD) was reduced 94.7% to 1.96 g L −1, fecal coliforms and Escherichia coli were reduced 99.2 and 97.1%, respectively, and grease removal was 99.9%. The average effluent pH (7.05) and alkalinity in T2.5 was within the optimal range for methanogens and increased significantly during the nine-month experiment, likely due to adaptation of the methanogenic organisms to the influent grease concentrations. Total nitrogen concentration decreased 34.0%, and NH 4-N increased 97.1% during digestion in T2.5, with no significant differences between T2.5 and T0. There was less phosphorus reduction with co-digestion, with 181 mg g −1 of total phosphorus (TP) in T2.5 and only 90.6 mg g −1 of TP in T0, resulting in lower N:P ratios in the grease treatment groups due to the greater concentration of phosphorus in the effluent.

Molecular Characterization of the Archaeal Community in an Amazonian Wetland Soil and Culture-Dependent Isolation of Methanogenic Archaea

Tropical wetlands are the major natural source of methane released into the atmosphere, producing about 60% of all natural emissions. The great wetland areas of the Amazon basin are the largest source of methane in this region, contributing an estimated 5% of the total emissions from the world’s flooded areas. However, despite the important role that methanogenic archaea play in these environments, there have been few studies on the composition of their archaeal communities. In this survey, four 16S rRNA archaeal clone libraries from different depths were constructed to examine the archaeal community in an Amazon wetland soil. A total of 599 clones were used to perform diversity and phylogenetic analyses. A broad, diverse archaeal community was found at the site, with the diversity decreasing as the depth increased (Shannon index range: 2.40–1.94). Phylogenetic analysis revealed sequences belonging to two archaeal phyla, with 65% classified as Crenarchaeota and 35% classified as Euryarchaeota. Within the Euryarchaeota group, most sequences were clustered into the Methanococci and Methanomicrobia classes, two groups of methanogens. Based on the abundance of methanogenic organisms, culture–dependent isolation was used to isolate these organisms. To enhance the growth of methanogenic archaea, a modified atmosphere (H2:CO2 = 80:20) was established combined with an anoxic environment for 18 months. Among the isolates, the genera Methanosarcina and Methanobacterium were detected throughout the anaerobic in vitro cultivation, indicating a possible role for these organisms in methane production. In conclusion, these exploratory molecular and culture–dependent approaches enhance our understanding of the archaeal community and methanogenic archaea living in wetland soils of the eastern Amazon and their role in methane production.

A methanogen hosted the origin of the genetic code

A comparison is made between orthologous proteins from a methanogen ( Methanopyrus kandleri) and from a non-methanogen ( Pyrococcus abyssi) in order to determine the amino acid substitution pattern. This analysis makes it possible to establish which amino acids are significantly and asymmetrically utilised by these two organisms. A methanophily index (MI) based on this asymmetry makes it possible for any protein to be associated with a numerical value which, when calculated for the same orthologous protein from methanogenic and non-methanogenic organisms, turns out to have the power to discriminate between these two groups of organisms, even if only for about 20% of the analysed proteins. The MI can also be associated to the genetic code under the assumption that the frequency of synonymous codons specifying the amino acids in the genetic code also reflects the frequency with which amino acids appeared in ancestral proteins. Finally a t-test shows that the MI value associated to the genetic code is not different from the mean value of the MI deriving from methanogen proteins, but it differs from the mean MI of non-methanogen proteins. This might indicate that the genetic code evolved in a methanogenic ‘organism’.

Methanolobus zinderi sp. nov., a methylotrophic methanogen isolated from a deep subsurface coal seam

A methanogenic organism from the domain Archaea (SD1(T)) was isolated from saline water released from a coal seam located 926 m below the surface via a methane-producing well near Monroe, Louisiana, USA. Growth and methanogenesis were supported with methanol, monomethylamine, dimethylamine or trimethylamine, but not with dimethylsulfide, formate, acetate or H(2)/CO(2). Cells grew in high-salt minimal medium but growth was stimulated with yeast extract or tryptone. Cells were single, non-motile, irregular coccoids 0.5-1.0 microm in diameter and the cell wall contained protein. Conditions for the maximum rate of growth were 40-50 degrees C, 0.2-0.6 M NaCl, 100->or=200 mM MgCl(2), and pH 7.0-8.0. The G+C content of the genomic DNA was 42+/-1mol %. A comparison of 16S rRNA gene sequences indicated that strain SD1(T) was most closely related to Methanolobus oregonensis DSM 5435(T) with 96 % gene sequence similarity. It is proposed that strain SD1(T) represents a novel species, Methanolobus zinderi sp. nov. The type strain is SD1(T) (=ATCC BAA-1601(T)=DSM 21339(T)).

Improved approach for transferring and cultivatingMethanosarcina acetivoransC2A (DSM 2834)

A method for cultivating Methanosarcina acetivorans was further developed to handle these anaerobic archaea without special equipment such as an anaerobic chamber. Medium was filtered and oxygen removed under a nitrogen gas-phase. A dithiothreitol-filled syringe was used to transfer cells from high density grown cultures to new medium. Growth time and cell mass were determined, as well as cell viability was proven by light microscopy. Cell transfer and growth was successful using this approach. This updated technique allows almost every laboratory the opportunity to grow these methanogenic organisms for further studies. The described method could be used for proteomic analysis and is also interesting for further protein structure determination.

Dominant sugar utilizers in sediment of Lake Constance depend on syntrophic cooperation with methanogenic partner organisms

Six strains of novel bacteria were isolated from profundal sediment of Lake Constance, a deep freshwater lake in Germany, by direct dilution of the sediment in mineral agar medium containing a background lawn of the hydrogen-scavenging Methanospirillum hungatei as a syntrophic partner. The numbers of colony-forming units obtained after incubation for more than 2 months were in the same range as those of total bacterial counts determined by DAPI staining (up to 10(8) cells per millilitre) suggesting that these organisms were dominant members of the community. Identical dilution series in the absence of methanogenic partners yielded numbers that were lower by two to three orders of magnitude. The dominant bacteria were isolated in defined co-culture with M. hungatei, and were further characterized. Growth was slow, with doubling times of 22-28 h at 28 degrees C. Cells were small, 0.5 x 5 microm in size, Gram-positive, and formed terminal oval spores. At 20 degrees C, glucose was fermented by the co-culture strain BoGlc83 nearly stoichiometrically to 2 mol of acetate and 1 mol of methane plus CO(2). At higher temperatures, also lactate and traces of succinate were formed. Anaerobic growth depended strictly on the presence of a hydrogen-scavenging partner organism and was inhibited by bromoethane sulfonate, which together indicate the need for a syntrophic partnership for this process. Strain BoGlc83 grew also aerobically in the absence of a partner organism. All enzymes involved in ATP formation via glycolysis and acetyl CoA were found, most of them at activities equivalent to the physiological substrate turnover rate. This new type of sugar-fermenting bacterium appears be the predominant sugar utilizer in this environment. The results show that syntrophic relationships can play an important role also for the utilization of substrates which otherwise can be degraded in pure culture.

Effects of bed materials on the performance of an anaerobic sequencing batch biofilm reactor treating domestic sewage

The objective of this study was to determine the best performance of an anaerobic sequencing batch biofilm reactor (AnSBBR) based on the use of four different bed materials as support for biomass immobilization. The bed materials utilized were polyurethane foam (PU), vegetal carbon (VC), synthetic pumice (SP), and recycled low-density polyethylene (PE). The AnSBBR, with a total volume of 7.2 L, was operated in 8-h batch cycles over 10 months, and fed with domestic sewage with an average influent chemical oxygen demand (COD) of 358±110 mg/L. The average effluent COD values were 121±31, 208±54, 233±52, and 227±51 mg/L, for PU, VC, SP, and PE, respectively. A modified first-order kinetic model was adjusted to temporal profiles of COD during a batch cycle, and the apparent kinetic constants were 0.52±0.05, 0.37±0.05, 0.80±0.04, and 0.30±0.02 h −1 for PU, VC, SP, and PE, respectively. Specific substrate utilization rates of 1.08, 0.11, and 0.86 mg COD/mg VS day were obtained for PU, VC, and PE, respectively. Although SP yielded the highest kinetic coefficient, PU was considered the best support, since SP presented loss of chemical constituents during the reactor's operational phase. In addition, findings on the microbial community were associated with the reactor's performance data. Although PE did not show a satisfactory performance, an interesting microbial diversity was found on its surface. Based on the morphology and denaturing gradient gel electrophoresis (DGGE) results, PE showed the best capacity for promoting the attachment of methanogenic organisms, and is therefore a material that merits further analysis. PU was considered the most suitable material showing the best performance in terms of efficiency of solids and COD removal.