Acetate Mineralization Research Articles

Microbiological Comparisons within and across Contiguous Lacustrine, Paleosol, and Fluvial Subsurface Sediments

Twenty-six subsurface samples were collected from a borehole at depths of 173.3 to 196.8 m in the saturated zone at the Hanford Site in south-central Washington State. The sampling was performed throughout strata that included fine-grained lacustrine (lake) sediments, a paleosol (buried soil) sequence, and coarse-grained fluvial (river) sediments. A subcoring method and tracers were used to minimize and quantify contamination to obtain samples that were representative of subsurface strata. Sediment samples were tested for total organic carbon, inorganic carbon, total microorganisms by direct microscopic counts, culturable aerobic heterotrophs by plate counts, culturable anaerobes by most-probable-number enumeration, basal respiration rates, and mineralization of (sup14)C-labeled glucose and acetate. Total direct microscopic counts of microorganisms were low, ranging from below detection to 1.9 x 10(sup5) cells g (dry weight)(sup-1). Culturable aerobes and anaerobes were below minimum levels of detection in most samples. Direct microscopic counts, basal respiration rates, and (sup14)C-glucose mineralization were all positively correlated with total organic carbon and were highest in the lacustrine sediments. In contrast to previous subsurface studies, these saturated-zone samples did not have higher microbial abundance and activities than unsaturated sediments sampled from the same borehole, the fine-textured lacustrine sediment had higher microbial numbers and activities than the coarse-textured fluvial sands, and the paleosol samples did not have higher biomass and activities relative to the other sediments. The results of this study expand the subsurface microbiology database to include information from an environment very different from those previously studied.

Stimulatory and toxic effects of acid, pentachlorophenol or zinc on the mineralization of acetate in acid or calcareous soils and subsoils

Abstract The toxic effects of pollutants on the soil microflora was studied as part of a research program aimed at the setting of soil quality standards. The effects of pentachlorophenol, zinc or hydrochloric acid on the mineralization of 1 μg/L [14C] acetate to 14CO2 was studied in an acid surface soil, an acid subsoil, an calcareous surface soil and a calcareous subsoil. The chalky surface soil was most sensitive for pentachlorophenol (PCP) which caused a marked stimulation of the 14CO2 production at low doses. The chalky subsurface soil was most sensitive for zinc. The chalky soil and subsoil neutralized added HCl more rapidly and showed a stronger sorption of zinc compared with the acidic soils. Nevertheless these soils showed a much higher sensitivity for acid, zinc and also for pentachlorophenol. The microflora of the acid surface soil were relatively resistant to acid, PCP or zinc. This resistant microflora showed a relatively low acetate mineralization rate.

Toxic effects of pollutants on the mineralization of acetate in methanogenic river sediment.

The highly industrialized drainage basin of the river has a total area of 160,000 km 2 before it enters the Netherlands (Van der Weijden and Middelburg 1989). About 58% of the river's load of suspended matter is deposited in sedimentation areas in the Netherlands (Admiraal and Van Zanten 1988) where the river eventually reaches the North Sea. These sediments are heavily polluted with persistent organic compounds and heavy metals and form a major environmental problem in the Netherlands. The Dutch research program on the 'Ecological Rehabilitation of the River Rhine included research on the effects of toxic compounds on the biodegradation in river sediments. The input of organic matter into the sediment is estimated to be I0' kg C yr -I (Admiraal and Van Zanten 1988). High numbers of bacteria are present (Van Beelen and Fleuren-Kemil~ 1989) and oxygen supplied by the overlying water will be rapidly consumed in the top layer of the sediment. The underlying part of the sediment is anoxic and there biodegradation of natural as well as anthropogenic organic substrates is dependent on anaerobic processes. Anaerobic mineralization of organic matter by micro-organisms is an essential component of the carbon cycle. Acetate is a key intermediate in anaerobic degradation of organic matter and a major component of anaerobic waste water. Organic polymers like proteins, carbohydrates, and lipids are hydrolysed to amino acids, sugars and fatty acids. These are converted by acidogenic bacteria which produce hydrogen, acetate, propionate, butyrate, lactate, and alcohols (Gorris 1987). Acetogenic bacteria convert these products to acetate. Hydrogen can be oxidized by hydrogenotrophic acetogens with the use of carbon dioxide to form acetate. Hydrogen and carbon dioxide are also used directly to form methane but about 70% of the methane formation in anaerobic freshwater sediments is derived from acetate (Lovley and Klug 1986). The following reaction is performed: CHsCOOH -> CH 4 + CO 2 AG ~ = -32.5 kJ/mol The energy liberated by this reaction is only 4% of the energy which is liberated upon the aerobic oxidation of acetate (Thauer et al. 1977). Hence the fraction of the acetate which is converted to biomass is small. During the aerobic mineralization of [14C] acetate about 50% of the label is converted to biomass while during the anaerobic mineralization 50% of the label is converted to methane. The mineralization of acetate under methanogenic conditions is performed by a few specialized methanogenic bacteria like Send reprint requests to Dr. P. van Beelen at the above address.

Degradation and mineralization of cellulose acetate in simulated thermophilic compost environments

Residual cellulose acetate (CA) films with initial degree of substitution (DS) values of 1.7 and 2.5 (CA DS-1.7 and DS-2.5) were recovered from a simulated thermophilic compost exposure and characterized by gel permeation chromatography (GPC), proton nuclear magnetic resonance (1H NMR), and scanning electron microscopy (SEM) to determine changes in polymer molecular weight and DS and to study microbial colonization and surface morphology, respectively. During the aerobic degradation of CA DS-1.7 and CA DS-2.5 films exposed for 7 and 18 days, respectively, the number-average molecular weight (Mn) of residual polymer decreased by 30.4% on day 5 and 20.3% on day 16, respectively. Furthermore, a decrease in the degree of substitution from 1.69 to 1.27 (4-day exposure) and from 2.51 to 2.18 (12-day exposure) was observed for the respective CA samples. In contrast, CA films (DS-1.7 and DS-2.5) which were exposed to abiotic control vessels for identical time periods showed no significant changes inMn and DS. SEM photographs of CA (DS-1.7 and DS-2.5) film surfaces after compost exposures revealed severe erosion and corresponding microbial colonization. Similar exposure times for CA films in abiotic control vessels resulted in only minor changes in surface characteristics by SEM observations. The conversion of CA DS-1.7 and DS-2.5 to CO2 was monitored by respirometry. In these studies, powdered CA was placed in a predigested compost matrix which was maintained at 53°C and 60% moisture content throughout the incubation period. A lag phase of 10- and 25-day duration for CA DS-1.7 and DS-2.5, respectively, was observed, after which the rate of degradation increased rapidly. Mineralization of exposed CA DS-1.7 and DS-2.5 powders reported as the percentage theoretical CO2 recovered reached 72.4 and 77.6% in 24 and 60 days, respectively. The results of this study demonstrated that microbial degradation of CA films exposed to aerobic thermophilic laboratory-scale compost reactors not only results in film weight loss but also causes severe film pitting and a corresponding decrease in chainMn and degree of substitution for the residual material. Furthermore, conversions to greater than 70% of the theoretical recovered CO2 for CA (DS 1.7 and 2.5) substrates indicate high degrees of CA mineralization.

Toxic Effects of Pentachlorophenol and Other Pollutants on the Mineralization of Acetate in Several Soils

The mineralization of [ 14C]acetate was studied in bottles with fresh soil and groundwater. Addition of toxicants inhibited the formation of 14CO 2 and dose-effect curves were obtained. The acetate mineralization was not inhibited by zinc, cadmium, K 2Cr 2O 7, chloropyrifos, and paraquat in an acid sandy soil at 1000 mg/kg dry soil. The IC 10 is the toxicant concentration which inhibits 10% of the initial mineralization rate. The IC 10 concentrations for 3,4-dichloroaniline, triphenyltin, and orthoxylene were 48, 96, and 730 mg/kg, respectively, in the acid sandy soil. The IC 10 of pentachlorophenol was measured in samples from the acid sandy soil and in several other soil and subsoil samples. The geometrical mean of the 13 IC 10 values was 16 mg pentachlorophenol/kg. A statistical method was used to calculate the PCP concentration above which 5% of the most sensitive acetate-mineralizing communities in all soils are influenced. The best estimate of this concentration is 0.3 mg PCP/kg but to be on the safe side the 95% confidence level of this concentration is 25 μg/kg.

Microbial abundance and activities in relation to water potential in the vadose zones of arid and semiarid sites

Numbers and activities of microorganisms were measured in the vadose zones of three arid and semiarid areas of the western United States, and the influence of water availability was determined. These low-moisture environments have vadose zones that are commonly hundreds of meters thick. The specific sampling locations chosen were on or near U.S. Department of Energy facilities: the Nevada Test Site (NTS), the Idaho National Engineering Laboratory (INEL), and the Hanford Site (HS) in southcentral Washington State. Most of the sampling locations were uncontaminated, but geologically representative of nearby locations with storage and/or leakage of waste compounds in the vadose zone. Lithologies of samples included volcanic tuff, basalt, glaciofluvial and fluvial sediments, and paleosols (buried soils). Samples were collected aseptically, either by drilling bore-holes (INEL and HS), or by excavation within tunnels (NTS) and outcrop faces (paleosols near the HS). Total numbers of microorganisms were counted using direct microscopy, and numbers of culturable microorganisms were determined using plate-count methods. Desiccation-tolerant microorganisms were quantified by plate counts performed after 24 h desiccation of the samples. Mineralization of (14)C-labeled glucose and acetate was quantified in samples at their ambient moisture contents, in dried samples, and in moistened samples, to test the hypothesis that water limits microbial activities in vadose zones. Total numbers of microorganisms ranged from log 4.5 to 7.1 cells g(-1) dry wt. Culturable counts ranged from log <2 to 6.7 CFU g(-1) dry wt, with the highest densities occurring in paleosol (buried soil) samples. Culturable cells appeared to be desiccation-tolerant in nearly all samples that had detectable viable heterotrophs. Water limited mineralization in some, but not all samples, suggesting that an inorganic nutrient or other factor may limit microbial activities in some vadose zone environments.

The toxic effects of pollutants on the mineralization of acetate in subsoil microcosms

AbstractThe mineralization of [14C]acetate or [14C]glucose was studied in aseptic subsoil samples at 10°C. At 1 μg/L and 100 μg/L, the mineralization showed first‐order kinetics preceded by a short lag phase. For the sandy subsurface soils, the half‐lives of acetate or glucose varied from 0.5 until 21 d, whereas a peat subsoil and a sandy surface soil produced half‐lives of 11 and 1.6 h, respectively.The EC50 is the toxicant concentration that causes 50% reduction of the percentage substrate mineralized at a certain incubation time and increases with time. The time‐independent toxicant concentration IC50 gives 50% inhibition of the mineralization rate and is equal to the EC50 at short incubation times. The IC50 of pentachlorophenol varied between 0.1 and 880 mg/kg subsoil. The aerobic mineralization of acetate in surface sand showed an IC50 of 28 mg pentachlorophenol/kg. Hydrochloric acid showed IC50 values ranging from pH 6.2 to pH 2.8. For chlorite and cadmium, the IC50 values were 34 and 59 mg/kg, respectively.When soils were incubated with 100 mg acetate/L, exponential growth kinetics were observed. Under these conditions the inhibitory effect of pentachlorophenol was relatively small because the resistant part of the acetate‐mineralizing microflora could grow and replace the inhibited part. The kinetics show why toxicity tests using high substrate concentrations are less sensitive than tests using more natural low substrate concentrations. The model predicts that slow‐growing microorganisms, which are vital to the functioning of the ecosystem, would recover only very slowly from the toxic effects of environmental pollution.

Kinetics of biodegradation of mixtures of substrates in soil

A number of organic compounds were added to soil to determine their effects on the mineralization of P-nitrophenol (PNP) by indigenous soil microorganisms. At a concentration of 10 μgg −1 of soil, phenol slowed the initial rate but increased the final extent of mineralization (cumulative evolution of 14CO 2) of 5 ng of radiolabeled PNP g −1 of soil, whereas glucose and glutamate had no effect. Glucose and glutamate at 500μg g −1 reduced the extent of PNP mineralization but did not change the shape of the mineralization curve. The reduction in extent was not a result of deficiencies of inorganic nutrients. The addition of phenol at 10μg g −1 of soil changed the curve of PNP mineralization from a nongrowth shape to a sigmoidal shape reflecting growth; however, no growth of the PNP-mineralizing population was indicated by most-probable-number counts. At 250 μg g −1 of soil, phenol prolonged the initial lag phase, the final extent of PNP mineralization and the abundance of PNP-mineralizing microorganisms. The simultaneous curves of phenol and PNP mineralization were fit by models describing the kinetics of mineralization of single and dual substrates, and the results indicate that the growth rates were the same for the populations using 5 ng PNP and 250 μg phenol g −1. Phenol at 10 and 250 μg g −1 was not toxic to the populations carrying out the initial mineralization of acetate or glucose at 5 ng g −1. The data show that growth on a second compound may substantially alter the kinetics of mineralization of low concentrations of organic chemicals in soil.

Impact of bioturbation by Arenicola marina on microbiological parameters in intertidal sediments

The impact of bioturbation by the lugworm Arenicola manna on sediment microflora and biochemical activities was investigated in intertidal sediments of the North Sea. Burrow walls and fecal casts were compared with surface and subsurface sediment surrounding the burrows. At the main study site burrow walls contained twice as much organic matter as the sediment surface. Viable counts of aerobic proteolytic and chitinolytic bacteria peaked at external and internal boundary layers (sediment surface and burrow walls). Burrow walls showed maximal bacterial production (incorporation of tritiated thymidine into DNA), maximal microheterotrophic activity (incorporation and mineralization of glucose and acetate) and highest levels of certain hydrolytic enzymes (alkaline phosphatase and sulfatase). Rates of chemoautotrophic COz fixation in both burrow walls and surrounding subsurface sedment were 3 to 4 times higher than at the sediment surface, suggesting a short-cucuited CO2 turnover driven by an elevated catabolism. In a second, more polluted study area, burrow walls were again the main site of microheterotrophic activity, but only minor differences were noted for CO2 fixation. Biogeochemical consequences of bioturbation by A, marina could be understood essentially as a shifting of catabolic and anabolic microbial activity peaks from the top to subsurface layers, where burrow walls showed the most conspicuous effects. Nevertheless, protease peaks in the fecal casts indicated also that this shifting pattern can be reversed for certain parameters.

Oxidation of short-chain fatty acids by sulfate-reducing bacteria in freshwater and in marine sediments.

Colony counts of acetate-, propionate- and L-lactate-oxidizing sulfate-reducing bacteria in marine sediments were made. The vertical distribution of these organisms were equal for the three types considered. The highest numbers were found just beneath the border of aerobic and anaerobic layers. Anaerobic mineralization of acetate, propionate and L-lactate was studied in the presence and in the absence of sulfate. In freshwater and in marine sediments, acetate and propionate were oxidized completely with concomitant reduction of sulfate. L-Lactate was always fermented. Lactate-oxidizing, sulfate-reducing bacteria could only be isolated from marine sediments, they belonged to the genus Desulfobacter and oxidized only acetate and ethanol by sulfate reduction. Propionate-oxidizing, sulfate-reducing bacteria belonged to the genus Desulfobulbus. They were isolated from freshwater as well as from marine sediments and showed a relatively large range of usable substrates: hydrogen, formate, propionate, L-lactate and ethanol were oxidized with concomitant sulfate reduction. L-Lactate and pyruvate could be fermented by most of the isolated strains.