Methanogenesis from acetate: enrichment studies

Fungal Solubilisation and Subsequent Microbial Methanation of Coal Processing Wastes

Large quantities of rejects from coal processing plants are currently disposed of as waste piles or in ponds and rivers, resulting in environmental concerns including pollution of rivers, and ground and surface water contamination. This work investigates for the first time, a two-stage microbial process for converting coal processing wastes (coal rejects) to methane, involving (1) fungal solubilisation of coal rejects and (2) microbial methanation of the solubilised products. Phanerochaete chrysosporium, Trichoderma viride and Neurospora discreta were screened for their ability to solubilise coal rejects. N. discreta was found to be the most suitable candidate based on the extent of bio-solubilisation, laccase activity and reversed-phase high-performance liquid chromatography (RP-HPLC) analysis. Bio-methanation of fungal-solubilised coal rejects was carried out in mesophilic anaerobic reactors with no additional carbon source, using inoculum from an anaerobic food digester. Coal rejects solubilised by N. discreta produced 3- to 6-fold higher methane compared to rejects solubilised by the other two fungi. No methane was produced from untreated coal rejects, demonstrating the importance of the fungal solubilisation stage. A total of 3.7 mmol of methane was generated per gram of carbon in 15 days from N. discreta-solubilised coal rejects. This process offers a timely, environment-friendly, and sustainable solution for the treatment of coal rejects and the generation of value-added products such as methane and volatile fatty acids.

Chemically Stressed Bacterial Communities in Anaerobic Digesters Exhibit Resilience and Ecological Flexibility

Anaerobic digestion is a technology known for its potential in terms of methane production. During the digestion process, multiple metabolites of high value are synthesized. However, recent works have demonstrated the high robustness and resilience of the involved microbiomes; these attributes make it difficult to manipulate them in such a way that a specific metabolite is predominantly produced. Therefore, an exact understanding of the manipulability of anaerobic microbiomes may open up a treasure box for bio-based industries. In the present work, the effect of nalidixic acid, γ-aminobutyric acid (GABA), and sodium phosphate on the microbiome of digested sewage sludge from a water treatment plant fed with glucose was investigated. Despite of the induced process perturbations, high stability was observed at the phylum level. However, strong variations were observed at the genus level, especially for the genera Trichococcus, Candidatus Caldatribacterium, and Phascolarctobacterium. Ecological interactions were analyzed based on the Lotka–Volterra model for Trichococcus, Rikenellaceae DMER64, Sedimentibacter, Candidatus Cloacimonas, Smithella, Cloacimonadaceae W5 and Longilinea. These genera dynamically shifted among positive, negative or no correlation, depending on the applied stressor, which indicates a surprisingly dynamic behavior. Globally, the presented work suggests a massive resilience and stability of the methanogenic communities coupled with a surprising flexibility of the particular microbial key players involved in the process.

Anaerobic degradability and acid hydrolysis of organic manure as an illustration of dietary organic matter utilization in cows in relation to lactation period

The objective of the present paper was to verify whether the method of studying the anaerobic degradability of organic matter of excrements could reveal the utilization of dietary organic matter in the digestive tract of ruminants in relation to the lactation period, and whether it could be replaced by a cheaper and easier method of acid hydrolysis of excrements. Changes in anaerobic degradability and hydrolysis yields of excrements were investigated in an experimental herd of 30 cows divided into two groups differing in their lactation period by 30 days. The results document that anaerobic degradability is a suitable indicator of anaerobic digestion conditions in the digestive tract of animals and of the fitness of their organism. However, the results of excrement hydrolysis according to the Rovira and Vallejo (2002) method were hardly reproducible and so they could not be used, when only the very labile organic fraction is evaluated. The evaluation of the sum of very labile fractions and semi-labile fraction provides easily available values, but these are only orientative values that cannot replace the costly and labour-consuming determination of anaerobic degradability of excrements.

Kinetic study and mathematical modeling of methanogenesis of acetate using pure cultures of methanogens

Kinetics of methanogenesis from acetate was studied using pure cultures of Methanosarcina barkeri and Methanosarcina mazei. Methane formation was found to be associated with cell growth. Nearly equimolar methane was produced from acetate during the methanogenic growth, and about 1.94 g of cells were formed from each mole of acetate consumed. Cell growth can be estimated from methane production. Significant substrate inhibition was found when acetate concentration was higher than 0.12 M. Among the three methanogenic strains studied, M. mazei strain S6 had the highest specific growth rate at all acetate concentrations studied and was least sensitive to environmental factors investigated (e.g., acetate concentration). The maximum specific growth rate found for strain S6 was 0.022 hr(-1) at acetic acid concentration around 7 g/L. The other two strains studied were M. barkeri strain 227 and strain MS. Growth of M. barkeri was completely inhibited at sodium acetate concentrations higher than 0.24 M. The maximum specific growth rate found for strains 227 and MS was 0.019 and 0.021 h(-1) at acetic acid concentrations of 3.6 and 6.8 g/L, respectively. A kinetic model with substrate inhibition was developed and can be used to simulate the methane formation from M. mazei strain S6 grown on acetate at 35 degrees C, pH 7.

Isolation and characterization of an h(2)-oxidizing thermophilic methanogen

A thermophilic methanogen was isolated from enrichment cultures originally inoculated with sludge from an anaerobic kelp digester (55 degrees C). This isolate exhibited a temperature optimum of 55 to 60 degrees C and a maximum near 70 degrees C. Growth occurred throughout the pH range of 5.5 to 9.0, with optimal growth near pH 7.2. Although 4% salt was present in the isolation medium, salt was not required for optimal growth. The thermophile utilized formate or H(2)-CO(2) but not acetate, methanol, or methylamines for growth and methanogenesis. Growth in complex medium was very rapid, and a minimum doubling time of 1.8 h was recorded in media supplemented with rumen fluid. Growth in defined media required the addition of acetate and an unknown factor(s) from digester supernatant, rumen fluid, or Trypticase. Cells in liquid culture were oval to coccoid, 0.7 to 1.8 mum in diameter, often occurring in pairs. The cells were easily lysed upon exposure to oxygen or 0.08 mg of sodium dodecyl sulfate per ml. The isolate was sensitive to tetracycline and chloramphenicol but not penicillin G or cycloserine. The DNA base composition was 59.69 mol% guanine plus cytosine.

Acetate as sole carbon and energy source for growth of methanosarcina strain 227

Methanosarcina strain 227 grew rapidly and produced methane on a mineral medium containing acetate as the sole added organic substrate. Cell yields but not doubling times were affected by the presence or absence of yeast extract. Greater cell yields occurred in yeast extract medium than in mineral medium. Radioactive labeling studies showed that acetate was decarboxylated in mineral medium, as was shown previously in complex medium. The specific radioactivity of methane produced per specific acitvity of acetate added was not significantly different in yeast extract medium compared with mineral medium. Unequivocal evidence indicates that the cleavage of acetate to methane and carbon dioxide provided the energy for growth in the presence or absence of other organic compounds; these latter compounds do not serve as energy sources, electron donors, or significant sources of methane during this aceticlastic reaction.

Terminal reactions in the anaerobic digestion of animal waste

An anaerobic mesophilic digestor was operated using beef cattle waste (diluted to 5.75% volatile solids) as substrate; retention time was 10 days with daily batch feed. Volatile solids destruction was 36%. Daily gas production rate was 1.8 liters of gas (standard temperature and pressure) per liter of digestor contents (0.99 liters of CH(4) per liter of digestor contents). Acetate turnover was measured, and it was calculated that 68% of the CH(4) was derived from the methyl group of acetate. When the methanogenic substrates acetic acid or H(2)/CO(2) were added to the digestor on a continuous basis, the microflora were able to adapt and convert them to terminal products while continuing to degrade animal waste to the same extent as without additions. The methanogenic substrates were added at a rate at least 1.5 times the microbial production rate which was measured in the absence of added substrates. Added acetate was converted directly to CH(4) by acetoclastic methanogens; H(2) addition greatly stimulated acetate production in the digestor. A method is described for the measurement of acetate turnover in batch-fed digestors.

Methanosarcina mazei LYC, a New Methanogenic Isolate Which Produces a Disaggregating Enzyme

A methanogenic coccoid organism, Methanosarcina mazei LYC, was isolated from alkaline sediment obtained from an oil exploration drilling site. The isolate resembled M. mazei S-6 by exhibiting different morphophases during its normal growth cycle. It differed from M. mazei S-6 by undergoint a spontaneous shift from large, irregular aggregates of cells to small, individual, irregular, coccoid units. In batch cultures at pH 7.0, M. mazei LYC grew as aggregates during the early growth stage. As the batch culture began exponential growth, the cell aggregates spontaneously dispersed: the culture liquid became turbid, and myriads of tiny (diameter, 1 to 3 mum) coccoid units were observed under phase-contrast microscopy. Disaggregation apparently was accomplished by the production of an enzyme which hydrolyzed the heteropolysaccharide component of the cell wall; the enzyme was active on other Methanosarcina strains as well. Although the enzyme was active when tested at pH 6.0, it apparently was not produced at that pH: when strain LYC was grown at pH 6.0, only cell aggregates were present throughout batch growth. Individual coccoid cells of M. mazei LYC were sensitive to sodium dodecyl sulfate, but the large aggregates of cells were not. Strain LYC rapidly used H(2)-CO(2), in addition to methanol, and mono-, di-, and trimethylamine as methanogenic substrates; acetate was used very slowly. Its optimum growth temperature was 40 degrees C, and its optimum pH was 7.2.

Effects of Organic Acid Anions on the Growth and Metabolism of Syntrophomonas wolfei in Pure Culture and in Defined Consortia

The effects of organic acid anions on the growth of Syntrophomonas wolfei was determined by varying the initial concentration of the acid anion in the medium. The addition of 15 mM acetate decreased the growth rate of a butyrate-catabolizing coculture containing Methanospirillum hungatei from 0.0085 to 0.0029 per hour. Higher initial acetate concentrations decreased the butyrate degradation rate and the yield of cells of S. wolfei per butyrate degraded. Inhibition was not due to the counter ion or the effect of acetate on the methanogen. Initial acetate concentrations above 25 mM inhibited crotonate-using pure cultures and cocultures of S. wolfei. Benzoate and lactate inhibited the growth of S. wolfei on crotonate in pure culture and coculture. Lactate was an effective inhibitor of S. wolfei cultures at concentrations greater than 10 mM. High concentrations of acetate and lactate altered the electron flow in crotonate-catabolizing cocultures, resulting in the formation of less methane and more butyrate and caproate. The inclusion of the acetate-using methanogen, Methanosarcina barkeri, in a methanogenic butyrate-catabolizing coculture increased both the yield of S. wolfei cells per butyrate degraded and the efficacy of butyrate degradation. Butyrate degradation by acetate-inhibited cocultures occurred only after the addition of Methanosarcina barkeri. These results showed that the metabolism of S. wolfei was inhibited by high levels of organic acid anions. The activity of acetate-using methanogens is important for the syntrophic degradation of fatty acids when high levels of acetate are present.

Isolation and Characterization of Haloanaerobacter chitinovorans gen. nov., sp. nov., a Halophilic, Anaerobic, Chitinolytic Bacterium from a Solar Saltern

Two halophilic anaerobic bacteria, one of which had chitinolytic activity, were isolated from a solar saltern in southern California. These organisms were long, gram-negative, motile, flexible rods. The biochemical and physiological characteristics of these bacteria were very similar but were different from the characteristics of other haloanaerobic bacteria. Both grew at salt concentrations ranging from 0.5 to 5 M and at temperatures ranging from 23 to 50 degrees C. They were sensitive to chloramphenicol but resistant to penicillin, carbenicillin, d-cycloserine, streptomycin, and tetracycline. An analysis of DNAs and whole-cell proteins showed that they were closely related taxonomically and distinguishable from other halophilic anaerobic bacteria. They exhibited 92.3 to 100% DNA homology as determined by DNA-DNA hybridization. The guanine-plus-cytosine contents of their DNAs were 34.8+/-1 mol%. The two isolates, strains W5C8 and W3C1, differed from other halophilic anaerobic bacteria sufficiently to support establishment of a new genus and species, Haloanaerobacter chitinovorans. Strain W5C8 exhibited chitinolytic activity and is designated the type strain. Two chitin-induced extracellular proteins with molecular weights of 38 x 10 and 40 x 10 were detected in strain W5C8.

Effect of H(2)-CO(2) on Methanogenesis from Acetate or Methanol in Methanosarcina spp

Growth of Methanosarcina sp. strain 227 and Methanosarcina mazei on H(2)-CO(2) and mixtures of H(2)-CO(2) and acetate or methanol was examined. The growth yield of strain 227 on H(2)-CO(2) in complex medium was 8.4 mg/mmol of methane produced. Growth in defined medium was characteristically slower, and cell yields were proportionately lower. Labeling studies confirmed that CO(2) was rapidly reduced to CH(4) in the presence of H(2), and little acetate was used for methanogenesis until H(2) was exhausted. This resulted in a biphasic pattern of growth similar to that reported for strain 227 grown on methanol-acetate mixtures. Biphasic growth was not observed in cultures on mixtures of H(2)-CO(2) and methanol, and less methanol oxidation occurred in the presence of H(2). In M. mazei the aceticlastic reaction was also inhibited by the added H(2), but since the cultures did not immediately metabolize H(2), the duration of the inhibition was much longer.

Methanogenesis from sucrose by defined immobilized consortia

A bacterial consortium capable of sucrose degradation primarily to CH(4) and CO(2) was constructed, with acetate as the key methanogenic precursor. In addition, the effect of agar immobilization on the activity of the consortium was determined. The primary fermentative organism, Escherichia coli, produced acetate, formate, H(2), and CO(2) (known substrates for methanogens), as well as ethanol and lactate, compounds that are not substrates for methanogens. Oxidation of the nonmethanogenic substrates, lactate and ethanol, to acetate was mediated by the addition of Acetobacterium woodii and Desulfovibrio vulgaris. The methanogenic stage was accomplished by the addition of the acetophilic methanogen Methanosarcina barkeri and the hydrogenophilic methanogen Methanobacterium formicicum. Results of studies with low substrate concentrations (0.05 to 0.2% [wt/vol]), a growth-limiting medium, and the five-component consortium indicated efficient conversion (40%) of sucrose carbon to CH(4). Significant decreases in yields of CH(4) and rates of CH(4) production were observed if any component of the consortium was omitted. Approximately 70% of the CH(4) generated occurred via acetate. Agar-immobilized cells of the consortium exhibited yields of CH(4) and rates of CH(4) production from sucrose similar to those of nonimmobilized cells. The rate of CH(4) production decreased by 25% when cysteine was omitted from reaction conditions and by 40% when the immobilized consortium was stored for 1 week at 4 degrees C.

Isolation and characterization of a moderately halophilic methanogen from a solar saltern

A moderately halophilic methanogenic bacterium was enriched with trimethylamine and isolated from the sediment of a solar salt pond (total dissolved solids of pond water, 250 g/liter; pH 7.5). The isolate (strain SF1, DSM 3243) was an irregular coccus which stained gram negative, with a diameter of 1 mum and a thin monolayered cell wall. The organism grew singly, in pairs, and in irregular clumps. Colonies were tannish yellow, circular, with entire edges, and about 1 mm in diameter within 1 week. Only methylamines or methanol was used for growth and methanogenesis. Most rapid growth (doubling time, 10.2 h) occurred at a temperature of 37 degrees C and a pH of 7.4. The optimum NaCl concentration was 2.1 M. Yeast extract or rumen fluid was required. The isolate was lysed by sodium dodecyl sulfate (0.1 g/liter) and was sensitive to chloramphenicol. The G+C content of the DNA was 41 (+/-1) mol%.

Isolation and Characterization of a Thermophilic Strain of Methanosarcina Unable to Use H(2)-CO(2) for Methanogenesis

A thermophilic strain of Methanosarcina, designated Methanosarcina strain TM-1, was isolated from a laboratory-scale 55 degrees C anaerobic sludge digestor by the Hungate roll-tube technique. Penicillin and d-cycloserine, inhibitors of peptidoglycan synthesis, were used as selective agents to eliminate contaminating non-methanogens. Methanosarcina strain TM-1 had a temperature optimum for methanogenesis near 50 degrees C and grew at 55 degrees C but not at 60 degrees C. Substrates used for methanogenesis and growth by Methanosarcina strain TM-1 were acetate (12-h doubling time), methanol (7- to 10-h doubling time), methanol-acetate mixtures (5-h doubling time), methylamine, and trimethylamine. When radioactively labeled acetate was the sole methanogenic substrate added to the growth medium, it was predominantly split to methane and carbon dioxide. When methanol was also present in the medium, the metabolism of acetate shifted to its oxidation and incorporation into cell material. Electrons derived from acetate oxidation apparently were used to reduce methanol. H(2)-CO(2) was not used for growth and methanogenesis by Methanosarcina strain TM-1. When presented with both H(2)-CO(2) and methanol, Methanosarcina strain TM-1 was capable of limited hydrogen metabolism during growth on methanol, but hydrogen metabolism ceased once the methanol was depleted. Methanosarcina strain TM-1 required a growth factor (or growth factors) present in the supernatant of anaerobic digestor sludge. Growth factor requirements and the inability to use H(2)-CO(2) are characteristics not found in other described Methanosarcina strains. The high numbers of Methanosarcina-like clumps in sludges from thermophilic digestors and the fast generation times reported here for Methanosarcina TM-1 indicate that Methanosarcina may play an important role in thermophilic methanogenesis.

Control of the Life Cycle of Methanosarcina mazei S-6 by Manipulation of Growth Conditions

The morphology of Methanosarcina mazei was controlled by magnesium, calcium, and substrate concentrations and by inoculum size; these factors allowed manipulation of the morphology and interconversions between pseudosarcinal aggregates and individual, coccoid cells. M. mazei grew as aggregates in medium with a low concentration of catabolic substrate (either 50 mM acetate, 50 mM methanol, or 10 mM trimethylamine) unless Ca and Mg concentrations were high. Growth in medium high in Ca, Mg, and substrate (i.e., 150 mM acetate, 150 mM methanol, or 40 mM trimethylamine) converted pseudosarcinal aggregates to individual cocci. In such media, aggregates separated into individual cells which continued to grow exclusively as single cells during subsequent transfers. Conversion of single cells back to aggregates was complicated, because conditions which supported the aggregated morphology (e.g., low calcium or magnesium concentration) caused lysis of coccoid inocula. We recovered aggregates from coccoid cells by inoculating serial dilutions into medium high in calcium and magnesium. Cells from very dilute inocula grew into aggregates which disaggregated on continued incubation. However, timely transfer of the aggregates to medium low in calcium, magnesium, and catabolic substrates allowed continued growth as aggregates. We demonstrated the activity of the enzyme (disaggregatase) which caused the dispersion of aggregates into individual cells; disaggregatase was produced not only during disaggregation but also in growing cultures of single cells. Uronic acids, the monomeric constituents of the Methanosarcina matrix, were also produced during disaggregation and during growth as coccoids.

Improved Technique for Identification and Enumeration of Methanogenic Bacterial Colonies on Roll Tubes by Epifluorescence Microscopy

Methanogenic fluorescent colonies can be clearly identified on roll tubes by using an epifluorescence microscope equipped with a × 2 objective. Methanogenic and nonmethanogenic colonies could be counted in roll tubes prepared from methanogenic enrichment cultures. Late-developing colonies appearing after 25 days of incubation were mainly methanogenic.

Methanogenic cleavage of acetate by lysates of Methanosarcina barkeri

Cell lysates of acetate-grown Methanosarcina barkeri 227 were found to cleave acetate to CH4 and CO2. The aceticlastic reaction was identified by using radioactive methyl-labeled acetate. Cell lysates decarboxylated acetate in a nitrogen atmosphere, conserving the methyl group in methane. The rate of methanogenesis from acetate in the cell lysates was comparable to that observed with whole cells. Aceticlastic activity was found in the particulate fraction seperate from methylcoenzyme M methylreductase activity, which occurs in the soluble fraction. Pronase treatment eliminated methylcoenzyme M methylreductase activity in lysates and stimulated aceticlastic activity, indicating the aceticlastic activity was not derived from unbroken cells, which are unaffected by proteolytic treatment.

Isolation and Characterization of an Anaerobic, Cellulolytic Bacterium, Clostridium cellulovorans sp. nov

A new anaerobic, mesophilic, spore-forming cellulolytic bacterium is described. Cellulose is cleared within 24 to 48 h around colonies formed in cellulose agar roll tubes. Cells stain gram negative and are nonmotile rods which form oblong spores either centrally or subterminally in a clostridial swelling. Colonies are irregular with an opaque edge and a center devoid of both vegetative cells and spores. Cellulose, xylan, pectin, cellobiose, glucose, maltose, galactose, sucrose, lactose, and mannose serve as substrates for growth. H 2 , CO 2 , acetate, butyrate, formate, and lactate are produced during fermentation of cellulose or cellobiose. The temperature and pH for optimum growth are 37°C and 7.0, respectively. The DNA composition is 26 to 27 mol% guanine plus cytosine. This bacterium resembles “ Clostridium lochheadii ” in morphological and some biochemical characteristics but is not identical to it. The name Clostridium cellulovorans sp. nov. is proposed. The type strain is 743B (ATCC 35296).

Hydrogen-using bacteria in a methanogenic acetate enrichment culture

In a study of the anaerobic utilization of acetate, an enrichment culture of sewage sludge organisms was initiated with calcium acetate as the sole carbon and energy source. A mixed bacterial population became established from which 14 anaerobic species were isolated. Two of the isolates were methanogenic bacteria but only one of these, Methanosarcina barkeri, utilised acetate as an energy source in axenic culture. The other methanogenic isolate, a Methanobacterium sp., utilised H2/CO2 but not acetate. A third methanogen, which was morphologically identical to Methanothrix soehngenii, was detected in the enrichment but was not obtained in monoculture. 2-Bromoethanesulphonate, a specific inhibitor of methanogenesis, completely inhibited the enrichment at a concentration of 10 mumol/l. Addition of H2 formate or methanol to the enrichment did not affect the rate of methanogenesis. An H2-utilizing Desulfovibrio sp. was also isolated from the enrichment.

Growth and methanogenesis by Methanosarcina strain 227 on acetate and methanol

Methanosarcina strain 227 exhibited exponential growth on sodium acetate in the absence of added H(2). Under these conditions, rates of methanogenesis were limited by concentrations of acetate below 0.05 M. One mole of methane was formed per mole of acetate consumed. Additional evidence from radioactive labeling studies indicated that sufficient energy for growth was obtained by the decarboxylation of acetate. Diauxic growth and sequential methanogenesis from methanol followed by acetate occurred in the presence of mixtures of methanol and acetate. Detailed studies showed that methanol-grown cells did not metabolize acetate in the presence of methanol, although acetate-grown cells did metabolize methanol and acetate simultaneously before shifting to methanol. Acetate catabolism appeared to be regulated in response to the presence of better metabolizable substrates such as methanol or H(2)-CO(2) by a mechanism resembling catabolite repression. Inhibition of methanogenesis from acetate by 2-bromoethanesulfonate, an analog of coenzyme M, was reversed by addition of coenzyme M. Labeling studies also showed that methanol may lie on the acetate pathway. These results suggested that methanogenesis from acetate, methanol, and H(2)-CO(2) may have some steps in common, as originally proposed by Barker. Studies with various inhibitors, together with molar growth yield data, suggest a role for electron transport mechanisms in energy metabolism during methanogenesis from methanol, acetate, and H(2)-CO(2).