Phylogeny of Acetate-Utilizing Microorganisms in Soils along a Nutrient Gradient in the Florida Everglades

The consumption of acetate in soils taken from a nutrient gradient in the northern Florida Everglades was studied by stable isotope probing. Bacterial and archaeal 16S rRNA gene clone libraries from eutrophic and oligotrophic soil microcosms strongly suggest that a significant amount of acetate is consumed by syntrophic acetate oxidation in nutrient-enriched soil.     

外源氧化铁对水稻土中有机酸含量的影响

在水稻土泥浆中添加Fe(OH) 3 可显著降低乙酸浓度 .在新鲜水稻土样品中 ,由于添加Fe(OH) 3导致对乙酸的竞争消耗 ,在培养 5d后 ,乙酸浓度降至 10～ 2 0 μmol·L-1的稳态浓度 ,而此刻对照中的乙酸浓度仍在 12 0 0 μmol·L-1以上 .在乙酸产生量较低的土壤中 ,添加Fe(OH) 3 可完全消耗体系中的乙酸 ,并导致产CH4过程的完全被抑制 .添加纤铁矿同样可使乙酸浓度显著减少 ,但作用效果不如无定形氧化铁 .添加赤铁矿可造成培养初期 (10d以内 )乙酸的大量积累 ,但并不引起产CH4量的增大 .添加Fe(OH) 3 、纤铁矿及铝取代针铁矿 ,能引起厌氧培养的水稻土中丙酸浓度的降低 ,其抑制效率为Fe(OH) 3 >纤铁矿 >铝取代针铁矿 .新鲜土样和经过 11周厌氧处理后的土样中 ,有机酸种类和含量有较大差别 .     

Acetogenic Capacities and the Anaerobic Turnover of Carbon in a Kansas Prairie Soil

To assess the anaerobic capacities of a temperate grassland soil, a Kansas prairie soil was incubated anaerobically as either soil-water (1:2) suspensions or as soil microcosms at 78% soil water-holding capacity. Prairie soil formed acetate and CO(inf2) as the two main initial carbonaceous products from the anaerobic turnover of endogenous organic matter. Metabolic capacities of soil suspensions and microcosms were similar. Rates of acetate formation from endogenous organic matter in soil-water suspensions incubated at 40, 30, and 15(deg)C approximated 3.3, 2.4, and 1.1 (mu)g of acetate per g (dry weight) of soil per h, respectively. Supplemental H(inf2) and CO(inf2) were subject to consumption with the apparent concomitant synthesis of acetate in both soil suspensions and soil microcosms. In soil microcosms, rates of H(inf2)-dependent acetogenesis at 30 and 55(deg)C were nearly equivalent. The uptake of supplemental H(inf2) was not coupled to methanogenesis under any condition examined. These anaerobic activities were relatively stable when soils were subjected to either aerobic drying or alternating periods of O(inf2) enrichment. On the basis of the formation of nitrogen (N(inf2)), denitrification was engaged during anaerobic incubation periods; nitrous oxide (N(inf2)O) was also formed under certain conditions. Although extended incubation of soil induced the delayed methanogenic turnover of acetate, acetate was subject to immediate turnover under either O(inf2)- or nitrate-enriched conditions. These studies support the following concepts: (i) obligately anaerobic bacteria such as acetogenic bacteria are stable to periods of aerobiosis and are active in the anaerobic microsites of oxic soils, and (ii) acetate synthesized in anaerobic microsites of oxic terrestrial soils constitutes a trophic link to both aerobic and anaerobic microbial communities.     

Effects of Environmental Parameters on the Formation and Turnover of Acetate by Forest Soils

The capacity to form acetate from endogenous matter was a common property of diverse forest soils when incubated under anaerobic conditions. At 15 to 20(deg)C, acetate synthesis occurred without appreciable delay when forest soils were incubated as buffered suspensions or in microcosms at various percentages of their maximum water holding capacity. Rates for acetate formation with soil suspensions ranged from 35 to 220 (mu)g of acetate per g (dry weight) of soil per 24 h, and maximal acetate concentrations obtained in soil suspensions were two- to threefold greater than those obtained with soil microcosms at the average water holding capacity of the soil. Cellobiose degradation in soil suspensions yielded H(inf2) as a transient product. Under anaerobic conditions, supplemental H(inf2) and CO(inf2) were directed towards the acetogenic synthesis of acetate, and enrichments yielded a syringate-H(inf2)-consuming acetogenic consortium. At in situ temperatures, acetate was a relatively stable anaerobic end product; however, extended incubation periods induced acetoclastic methanogenesis and sulfate reduction. Higher mesophilic and thermophilic temperatures greatly enhanced the capacity of soils to form methane. Although methanogenic and sulfate-reducing activities under in situ-relevant conditions were negligible, these findings nonetheless demonstrated the occurrence of methanogens and sulfate-reducing bacteria in these aerated terrestrial soils. In contrast to the protracted stability of acetate under anaerobic conditions at 15 to 20(deg)C with unsupplemented soils, acetate formed by forest soils was rapidly consumed in the presence of oxygen and nitrate, and substrate-product stoichiometries indicated that acetate turnover was coupled to oxygen-dependent respiration and denitrification. The collective results suggest that acetate formed under anaerobic conditions might constitute a trophic link between anaerobic and aerobic processes in forest soils.     

Acetate synthesis in soil from a bavarian beech forest

Soil obtained from a beech forest formed significant amounts of acetate when incubated in a bicarbonate-buffered, mineral salt solution under anaerobic conditions at both 5 and 20 degrees C (21 and 38 g of acetate per kg [dry weight] of soil, respectively). At 20 degrees C, following an 18-day lag period, rates of 0.07 mmol of acetate synthesized per g (dry weight) of soil per day were observed. Acetate was not subject to immediate turnover; methane and hydrogen were not formed during the time intervals (5 degrees C, 335 days; 20 degrees C, 95 days) evaluated. The synthesis of acetate from endogenous materials was coincident with acetogenic potentials, i.e., the capacity to catalyze the H(2)-dependent synthesis of acetate. Hydrogen consumption was not directed towards the synthesis of methane. Collectively, these results suggest that acetogenesis may be an underlying microbial activity of this forest soil.     

Microbial Activity in Organic Soils as Affected by Soil Depth and Crop

The microbial activity of Pahokee muck, a lithic medisaprist, and the effect of various environmental factors, such as position in the profile and type of plant cover, were examined. Catabolic activity for [7-¹⁴C]salicylic acid, [1,4-¹⁴C]succinate, and [1,2-¹⁴C]acetate remained reasonably constant in surface (0 to 10 cm) soil samples from a fallow (bare) field from late in the wet season (May to September) through January. Late in January, the microbial activity toward all three compounds decreased approximately 50%. The microbial activity of the soil decreased with increasing depth of soil. Salicylate catabolism was the most sensitive to increasing moisture deep in the soil profile. At the end of the wet season, a 90% decrease in activity between the surface and the 60- to 70-cm depth occurred. Catabolism of acetate and succinate decreased approximately 75% in the same samples. Little effect of crop was observed. Variation in the microbial activity, as measured by the catabolism of labeled acetate, salicylate, or succinate, was not significant between a sugarcane (Saccharum officinarum L.) field and a fallow field. The activity with acetate was insignificantly different in a St. Augustine grass [Stenotaphrum secundatum (Walt) Kuntz] field, whereas the catabolism of the remaining substrates was elevated in the grass field. These results indicate that the total carbon evolved from the different levels of the soil profile by the microbial community oxidizing the soil organic matter decreased as the depth of the soil column increased. However, correction of the amount of carbon yielded at each level for the bulk density of that level reveals that the microbial contribution to the soil subsidence is approximately equivalent throughout the soil profile above the water table.     

Effect of nitrate, acetate, and hydrogen on native perchlorate-reducing microbial communities and their activity in vadose soil

The effect of nitrate, acetate, and hydrogen on native perchlorate-reducing bacteria (PRB) was examined by conducting microcosm tests using vadose soil collected from a perchlorate-contaminated site. The rate of perchlorate reduction was enhanced by hydrogen amendment and inhibited by acetate amendment, compared with unamendment. Nitrate was reduced before perchlorate in all amendments. In hydrogen-amended and unamended soils, nitrate delayed perchlorate reduction, suggesting that the PRB preferentially use nitrate as an electron acceptor. In contrast, nitrate eliminated the inhibitory effect of acetate amendment on perchlorate reduction and increased the rate and the extent, possibly because the preceding nitrate reduction/denitrification decreased the acetate concentration that was inhibitory to the native PRB. In hydrogen-amended and unamended soils, perchlorate reductase gene (pcrA) copies, representing PRB densities, increased with either perchlorate or nitrate reduction, suggesting that either perchlorate or nitrate stimulates the growth of the PRB. In contrast, in acetate-amended soil pcrA increased only when perchlorate was depleted: a large portion of the PRB may have not utilized nitrate in this amendment. Nitrate addition did not alter the distribution of the dominant pcrA clones in hydrogen-amended soil, likely because of the functional redundancy of PRB as nitrate-reducers/denitrifiers, whereas acetate selected different pcrA clones from those with hydrogen amendment.     

Metabolism of position-labelled glucose in anoxic methanogenic paddy soil and lake sediment

Abstract Turnover times of radioactive glucose were shorter in paddy soil (4–16 min) than in Lake Constance sediment (18–62 min). In the paddy soil, 65–75% of the radioactive glucose was converted to soluble metabolites. In the sediment, only about 25% of the radioactive glucose was converted to soluble metabolites, the rest to particulate material. In anoxic paddy soil, the degradation pattern of position-labelled glucose was largely consistent with glucose degradation via the Embden-Meyerhof-Parnas (EMP) pathway followed by methanogenic acetate cleavage: CO₂ mainly originated from C-3,4, whereas CH₄ mainly originated from C-1 and C-6 of glucose. Acetate-carbon originated from C-1, C-2 and C-6 rather than from C-3,4 of glucose. In both paddy soil and Lake Constance sediment acetate and CO₂ were the most important early metabolites of radioactive glucose. Other early products included propionate, ethanol/butyrate, succinate, and lactate, but accounted each for less than 1–8% of the glucose utilized. The labelling of propionate by [3,4-¹⁴C]glucose suggests that it was mainly produced from glucose or lactate rather than from ethanol. Isopropanol and caproate were also detectable in paddy soil, but were not produced from radioactive glucose. Chloroform inhibited methanogenesis, inhibited the further degradation of radioactive acetate and resulted in the accumulation of H₂, however, did not inhibit glucose degradation. Since acetate was the main soluble fermentation product of glucose and was produced at a relatively high molar acetate: CO₂ ratio (2.5:1), homoacetogenesis appeared to be the most important glucose fermentation pathway.     

Reduction of perchlorate and nitrate by microbial communities in vadose soil

Perchlorate contamination is a concern because of the increasing frequency of its detection in soils and groundwater and its presumed inhibitory effect on human thyroid hormone production. Although significant perchlorate contamination occurs in the vadose (unsaturated) zone, little is known about perchlorate biodegradation potential by indigenous microorganisms in these soils. We measured the effects of electron donor (acetate and hydrogen) and nitrate addition on perchlorate reduction rates and microbial community composition in microcosm incubations of vadose soil. Acetate and hydrogen addition enhanced perchlorate reduction, and a longer lag period was observed for hydrogen (41 days) than for acetate (14 days). Initially, nitrate suppressed perchlorate reduction, but once perchlorate started to be degraded, the process was stimulated by nitrate. Changes in the bacterial community composition were observed in microcosms enriched with perchlorate and either acetate or hydrogen. Denaturing gradient gel electrophoresis analysis and partial sequencing of 16S rRNA genes recovered from these microcosms indicated that formerly reported perchlorate-reducing bacteria were present in the soil and that microbial community compositions were different between acetate- and hydrogen-amended microcosms. These results indicate that there is potential for perchlorate bioremediation by native microbial communities in vadose soil.     

Pattern of non-methanogenic and methanogenic degradation of cellulose in anoxic rice field soil

Rice field soils turn anoxic upon flooding. The complete mineralization of organic matter, e.g. cellulose, to gaseous products is then accomplished by the sequential reduction of nitrate, ferric iron, sulfate and finally by methanogenesis. Therefore, the anaerobic turnover of [U-(14)C]cellulose was investigated in fresh, non-methanogenic and in preincubated, methanogenic slurries of Italian rice field soil. In anoxic soil slurries freshly prepared from air-dried soil [U-(14)C]cellulose was converted to (14)CO(2) and (14)CH(4) in a ratio of 3:1. In methanogenic soil slurries, on the other hand, which had been preincubated for 45 days under anaerobic conditions, [U-(14)C]cellulose was converted to (14)CO(2) and (14)CH(4) in the ratio of 1:1. The turnover times (7-14 days) of cellulose degradation were not significantly different (P0.05) in fresh and methanogenic soil. Chloroform addition abolished CH(4) production, but only slightly (30%) inhibited cellulose degradation in both fresh and methanogenic soil. Under both soil conditions, [(14)C]acetate was the only labeled intermediate detected. A maximum of 24% of the applied radioactivity was transiently accumulated as [(14)C]acetate in both fresh and methanogenic soil slurries. However, when methanogenesis was inhibited by chloroform, 46% and 66% of the applied radioactivity were recovered as [(14)C]acetate in fresh and methanogenic soil, respectively. Only non-radioactive propionate accumulated during the incubation with [U-(14)C]cellulose, especially in the presence of chloroform, indicating that propionate was produced from substrates other than cellulose.     

Reduction of Perchlorate and Nitrate by Microbial Communities in Vadose Soil

Perchlorate contamination is a concern because of the increasing frequency of its detection in soils and groundwater and its presumed inhibitory effect on human thyroid hormone production. Although significant perchlorate contamination occurs in the vadose (unsaturated) zone, little is known about perchlorate biodegradation potential by indigenous microorganisms in these soils. We measured the effects of electron donor (acetate and hydrogen) and nitrate addition on perchlorate reduction rates and microbial community composition in microcosm incubations of vadose soil. Acetate and hydrogen addition enhanced perchlorate reduction, and a longer lag period was observed for hydrogen (41 days) than for acetate (14 days). Initially, nitrate suppressed perchlorate reduction, but once perchlorate started to be degraded, the process was stimulated by nitrate. Changes in the bacterial community composition were observed in microcosms enriched with perchlorate and either acetate or hydrogen. Denaturing gradient gel electrophoresis analysis and partial sequencing of 16S rRNA genes recovered from these microcosms indicated that formerly reported perchlorate-reducing bacteria were present in the soil and that microbial community compositions were different between acetate- and hydrogen-amended microcosms. These results indicate that there is potential for perchlorate bioremediation by native microbial communities in vadose soil.     

铅对几种作物生长的影响及其在植物体内的积累

根据将醋酸铅溶液施入土壤及喷洒叶片的盆栽试验可以确定：(1)铅对植物的毒性不大,植物对铅的忍耐力很强。目前自然界中的铅污染程度不足以直接伤害植物本身。(2)溶液中的铅可以被植物的根系吸收,也可以被叶片直接吸收。吸收量与环境中的铅浓度成正比。(3)铅在植物体中移动性很小,根吸收的铅主要积累在根部,叶片吸收的铅主要积累在叶部。有少量铅可以向上或向下转移,但极少能进入果实的内部及块根的淀粉中。     

Bicarbonate-dependent production and methanogenic consumption of acetate in anoxic paddy soil

Abstract Acetate turnover was measured in slurries of anoxic methanogenic paddy soil after addition of carrier-free [2-¹⁴C]-acetate. Acetate concentrations stayed fairly constant for about 1–2 days indicating steady state between production and consumption reactions. Depending on the experiment, acetate concentrations were between 100 and 3000 μM. Turnover rates were determined from the logarithmic decrease of [2-¹⁴C]-acetate or from the accumulation of acetate in the presence of chloroform resulting in similar values, i.e. 12–13 nmol h⁻¹g⁻¹d.w. soil at 17°C and 36–88 nmol h⁻¹g⁻¹d.w. at 30°C. Acetate consumption was completely inhibited by chloroform. The respiratory index (RI) was < 0.27. Hence, acetate was apparently consumed by methanogenic bacteria. About 80–90% of the CH₄ produced originated from the methyl group of acetate. The role of homoacetogenesis for acetate production was studied by measuring the incorporation of radioactive bicarbonate into acetate. In different experiments, CO₂ incorporation accounted for fractions of 1–60% of the acetate produced, about 10% being the most likely value for steady-state conditions. The fraction increased at high H₂ concentrations and decreased at high acetate concentrations. The rate of H₂ production that was required for chemolithotrophic acetate production from CO₂ was two orders of magnitude higher than the actually measured rate. Hence, most of the CO₂ incorporation into acetate was caused by electron donors other than H₂ (e.g., carbohydrates) and/or by exchange reactions.     

The occurrence and ecology of microbial chain elongation of carboxylates in soils

Chain elongation is a growth-dependent anaerobic metabolism that combines acetate and ethanol into butyrate, hexanoate, and octanoate. While the model microorganism for chain elongation, Clostridium kluyveri, was isolated from a saturated soil sample in the 1940s, chain elongation has remained unexplored in soil environments. During soil fermentative events, simple carboxylates and alcohols can transiently accumulate up to low mM concentrations, suggesting in situ possibility of microbial chain elongation. Here, we examined the occurrence and microbial ecology of chain elongation in four soil types in microcosms and enrichments amended with chain elongation substrates. All soils showed evidence of chain elongation activity with several days of incubation at high (100 mM) and environmentally relevant (2.5 mM) concentrations of acetate and ethanol. Three soils showed substantial activity in soil microcosms with high substrate concentrations, converting 58% or more of the added carbon as acetate and ethanol to butyrate, butanol, and hexanoate. Semi-batch enrichment yielded hexanoate and octanoate as the most elongated products and microbial communities predominated by C. kluyveri and other Firmicutes genera not known to undergo chain elongation. Collectively, these results strongly suggest a niche for chain elongation in anaerobic soils that should not be overlooked in soil microbial ecology studies.Subject terms: Soil microbiology, Microbial ecology     

Measurement of Monosaccharides and Conversion of Glucose to Acetate in Anoxic Rice Field Soil

Degradation of glucose has been implicated in acetate production in rice field soil, but the abundance of glucose, the temporal change of glucose turnover, and the relationship between glucose and acetate catabolism are not well understood. We therefore measured the pool sizes of glucose and acetate in rice field soil and investigated the turnover of [U-¹⁴C]glucose and [2-¹⁴C]acetate. Acetate accumulated up to about 2 mM during days 5 to 10 after flooding of the soil. Subsequently, methanogenesis started and the acetate concentration decreased to about 100 to 200 μM. Glucose always made up >50% of the total monosaccharides detected. Glucose concentrations decreased during the first 10 days from 90 μM initially to about 3 μM after 40 days of incubation. With the exception at day 0 when glucose consumption was slow, the glucose turnover time was in the range of minutes, while the acetate turnover time was in the range of hours. Anaerobic degradation of [U-¹⁴C]glucose released [¹⁴C]acetate and ¹⁴CO₂ as the main products, with [¹⁴C]acetate being released faster than ¹⁴CO₂. The products of [2-¹⁴C]acetate metabolism, on the other hand, were ¹⁴CO₂ during the reduction phase of soil incubation (days 0 to 15) and ¹⁴CH₄ during the methanogenic phase (after day 15). Except during the accumulation period of acetate (days 5 to 10), approximately 50 to 80% of the acetate consumed was produced from glucose catabolism. However, during the accumulation period of acetate, the rate of acetate production from glucose greatly exceeded that of acetate consumption. Under steady-state conditions, up to 67% of the CH₄ was produced from acetate, of which up to 56% was produced from glucose degradation.     

Transport of ammonium and nitrate in saturated porous media incorporating physiobiotransformations and bioclogging

The vertical transport of nitrates from fertilizer application and wastewater irrigation through the subsurface and saturated zone is of major concern to assess the vulnerability of groundwater contamination. The present study addresses the transport of nitrogenous fertilizers such as ammonium and nitrate in the presence of organic carbon (acetate) in a one-dimensional soil column under saturated conditions, considering the effect of adsorption and biotransformation. The soil had a neutral pH range and was classified as loamy sand, with a 0.89% organic carbon content. Batch studies revealed that sorption occurred in the order of ammonium > acetate > nitrate following a Freundlich isotherm model. Mixed heterotrophic native soil bacteria for aerobic nitrification and anoxic denitrification were developed, and the growth kinetic parameters were simulated using a Haldane inhibition model for nitrification and a Monod inhibition model for denitrification. Results from biotransformation studies suggested that denitrification was the predominant process, with significant bacterial growth and clogging of pores occurring monotonously reaching a stationary phase by 12 days. Pore-clogging phenomenon not only reduces the permeability of the soil by 5 orders of magnitude but also increases the contact time of the contaminant with the soil microbe and thereby delays the transport process and decreases the effluent ammonium and nitrate concentrations. A tailing breakthrough in a leaching study illustrates that water flux variation (0.153 and 0.509 cm/min) did not influence the transport of solutes, rather irreversible chemical bonding retains more ammonium than nitrate in the soil matrix.     

Localization of processes involved in methanogenic degradation of rice straw in anoxic paddy soil

In anoxic paddy soil, rice straw is decomposed to CH(4) and CO(2) by a complex microbial community consisting of hydrolytic, fermenting, syntrophic and methanogenic microorganisms. Here, we investigated which of these microbial groups colonized the rice straw and which were localized in the soil. After incubation of rice straw in anoxic soil slurries for different periods, the straw pieces were removed from the soil, and both slurry and straw were studied separately. Although the potential activities of polysaccharolytic enzymes were higher in the soil slurry than in the straw incubations, the actual release of reducing sugars was higher in the straw incubations. The concentrations of fermentation products, mainly acetate and propionate, increased steadily in the straw incubations, whereas only a little CH(4) was formed. In the soil slurries, on the other hand, fermentation products were low, whereas CH(4) production was more pronounced. The production of CH(4) or of fermentation products in the separated straw and soil incubations accounted in sum for 54-82% of the CH(4) formed when straw was not removed from the soil. Syntrophic propionate degradation to acetate, CO(2) and H(2) was thermodynamically more favourable in the soil than in the straw fraction. These results show that hydrolysis and primary fermentation reactions were mainly localized on the straw pieces, whereas the syntrophic and methanogenic reactions were mainly localized in the soil. The percentage of bacterial relative to total microbial 16S rRNA content was higher on the straw than in the soil, whereas it was the opposite for the archaeal 16S rRNA content. It appears that rice straw is mainly colonized by hydrolytic and fermenting bacteria that release their fermentation products into the soil pore water where they are further degraded to CH(4). Hence, complete methanogenic degradation of straw in rice soil seems to involve compartmentalization.     

Occurrence of Isocitrate Lyase in a Thermophilic Bacillus Species

A thermophilic, sporeforming bacterium has been isolated from soil on a medium containing acetate as a carbon source. This organism is similar to Bacillus stearothermophilus in most respects but differs in its inability to hydrolyze starch. Isocitrate lyase is present in cell-free extracts of organisms grown in a medium with acetate as a carbon source. The specific activity was 400 times lower in extracts of organisms utilizing glucose as a carbon source. With crude extracts, enzyme activity was strongly stimulated by Mg(++), but cysteine and ethylenediaminetetraacetate had little effect. It appeared to be more heat-stable than the pure isocitrate lyase from Pseudomonas indigofera.     

Effect of several environmental parameters on carbon metabolism in histosols

High specific activity¹⁴C-labeled glucose, succinate, acetate, salicylate, and amino acids were used to examine carbon metabolism by the microbial community of Pahokee muck (aLithic medisaprist), a drained, cultivated soil of the Florida Everglades. Variations in carbon oxidation were observed from the end of the wet season through the dry season in a fallow (bare) field. Evolution of¹⁴CO₂ varied with the substrate added and time. Calculation of¹⁴CO₂ evolution for each substrate as a proportion of total respiration of the microbial community which was measured by succinate oxidation (relative oxidation) allowed for determination of the proportion of metabolic activity contributed by the oxidation of each carbon source. Except for the May sample when an approximate 30% decline in relative salicylate oxidation activity was observed, the proportion of total catabolic activity contributed by salicylate oxidation and acetate degradation was constant with time. Relative oxidation of glucose and amino acids ranged from 0.12 to 0.52 and 0.10 to 0.23, respectively. At two times during the dry season, the effect of depth of soil and crop on the carbon oxidation was examined. Relative acetate and amino acid oxidation were constant with depth whereas statistically significant variation was observed in glucose and salicylate oxidation. Generally, with the latter substrates, the activity declined with increased soil depth. Greatest effect of crop on these metabolic activities was noted with oxidation of salicylate in soils from a St. Augustinegrass [Stenatophrum secundatum (Walt.) Kuntz] pasture. In these soils, oxidation of salicylate was nearly double that of the fallow field or of soil planted with sugarcane (Saccharum sp.).     

Methanol as the Primary Methanogenic and Acetogenic Precursor in the Cold Zoige Wetland at Tibetan Plateau

Previous studies suggested that methanol and acetate were the likely methanogenic precursors in the cold Zoige wetland. In this study, the contribution of the two substances to methanogenesis and the conversion in Zoige wetland were analyzed. It was determined that methanol supported the highest CH₄ formation rate in the enrichments of the soil grown with Eleocharis valleculosa, and even higher at 15°C than at 30°C; while hydrogenotrophic methanogenesis was higher at 30°C. Both methanol- and acetate-using methanogens were counted at the highest (10⁷ g⁻¹) in the soil, whereas methanol-using acetogens (10⁸ g⁻¹) were ten times more abundant than either methanol- or acetate-using methanogens. Both methanol and acetate were detected in the methanogenesis-inhibited soil samples, so that both could be the primary methanogenic precursors in E. valleculosa soil. However, the levels of methanol and acetate accumulated in 2-bromoethane-sulfonate (BES)- and CHCl₃-treated soils were in reverse, i.e., higher methanol in CHCl₃- and higher acetate in BES-treated soil, so that methanol-derived methanogenesis could be underestimated due to the consumption by acetogens. Analysis of the soil 16S rRNA genes revealed Acetobacterum bakii and Trichococcus pasteurii to be the dominant methanol-using acetogens in the soil, and a strain of T. pasteurii was isolated, which showed the high conversion of methanol to acetate at 15°C.