Microbiological Degradation of Asymmetric Dimethylhydrazine,a Toxic Rocket Fuel Ingredient

The possibility of microbiological cleaning of water and soil polluted with asymmetric dimethylhydrazine (ADMH), a highly toxic ingredient of rocket fuel (IRF), was studied. Several isolates (bacteria, yeast, and micromycetes) capable of utilizing ADMH as the only source of nitrogen, carbon, and energy were isolated from IRF-polluted tundra soil. Acceleration of IRF biodegradation was achieved using a biosorbent that involved cells of the degrader strain immobilized on granulated activated charcoal. Biological testing in Escherichia coli and cereals (wheat and barley) demonstrated that biodegradation significantly decreased the integral toxicity of solutions containing ADMH, suggesting its utility for microbiological cleaning of polluted territories.     

Bioremediation of diesel-contaminated soils: Evaluation of potential in situ techniques by study of bacterial degradation

The development of a simple laboratory methodology allows theimplementation of in situbioremediation of polluted soils with diesel fuel. In thisinvestigation microbiological and chemical analyses and a suitable bioreactor design, were veryuseful for suggesting the best ways to improve biodegradation extents in a diesel-enrichedsoil. Biostimulation with inorganic nitrogen and phosphorus produced the best resultsin a simple bioreactor, with biodegradation extents higher than 90% after 45 days. Also,the addition of activated sludge from a domestic wastewater plant increased the degradationrate to a great extent. In both cases, microbiological studies showed the presence ofAcinetobacter sp. degrading most of thehydrocarbons. Simultaneously, a diesel fuel release(approximately 400,000 l) was studied. Samples taken in polluted soil and water revealed thatbacteria from the genus Acinetobacterwere predominant. In plate studies, Acinetobacter coloniesproduced a whitish substance with the characteristics of a biosurfactant. Remarkably, thepresence of this product was evident at the field site, both in the riverbanks and in the physicalrecovery plant. The study of the similarities between laboratory results and the diesel spillsite strongly suggested that natural conditions at the field site allowed the implementationof in situ bioremediation after physical removal of LNAPL (light nonaqueous-phase liquids).     

Spatial distribution of bacterial communities and phenanthrene degradation in the rhizosphere of Lolium perenne L

Rhizodegradation of organic pollutants, such as polycyclic aromatic hydrocarbons, is based on the effect of root-produced compounds, known as exudates. These exudates constitute an important and constant carbon source that selects microbial populations in the plant rhizosphere, modifying global as well as specific microbial activities. We conducted an experiment in two-compartment devices to show the selection of bacterial communities by root exudates and phenanthrene as a function of distance to roots. Using direct DNA extraction, PCR amplification, and thermal gradient gel electrophoresis screening, bacterial population profiles were analyzed in parallel to bacterial counts and quantification of phenanthrene biodegradation in three layers (0 to 3, 3 to 6, and 6 to 9 mm from root mat) of unplanted-polluted (phenanthrene), planted-polluted, and planted-unpolluted treatments. Bacterial community differed as a function of the distance to roots, in both the presence and the absence of phenanthrene. In the planted and polluted treatment, biodegradation rates showed a strong gradient with higher values near the roots. In the nonplanted treatment, bacterial communities were comparable in the three layers and phenanthrene biodegradation was high. Surprisingly, no biodegradation was detected in the section of planted polluted treatment farthest from the roots, where the bacterial community structure was similar to those of the nonplanted treatment. We conclude that root exudates and phenanthrene induce modifications of bacterial communities in polluted environments and spatially modify the activity of degrading bacteria.     

Degradation of benzyldimethylalkylammonium chloride by Aeromonas hydrophila sp. K

AIMS: The aim of this work was to study the biodegradation of benzyldimethylalkylammonium chloride (BAC) by Aeromonas hydrophila sp. K, an organism isolated from polluted soil and capable of utilizing BAC as sole source of carbon and energy. METHODS AND RESULTS: High performance liquid chromatography and gas chromatography-mass spectrometry (GC-MS) analysis was used to study BAC degradation pathway. It was shown that during BAC biodegradation, formation of benzyldimethylamine, benzylmethylamine, benzylamine, benzaldehyde and benzoic acid occurred. Formation of benzyldimethylamine as the initial metabolite suggested that the cleavage of Calkyl-N bond occurred as the first step of BAC catabolism. Liberation of benzylmethylamine and benzylamine likely resulted from subsequent demethylation reactions, followed by deamination with formation of benzaldehyde. Benzaldehyde was rapidly converted into benzoic acid, which was further degraded. CONCLUSIONS: Aer. hydrophila sp. K is able to degrade BAC. A degradation pathway for BAC and related compounds is proposed. SIGNIFICANCE AND IMPACT OF STUDY: These findings are significant for understanding biodegradation pathways of benzyl-containing quaternary ammonium compounds.     

Spatial Distribution of Bacterial Communities and Phenanthrene Degradation in the Rhizosphere of Lolium perenne L.

Rhizodegradation of organic pollutants, such as polycyclic aromatic hydrocarbons, is based on the effect of root-produced compounds, known as exudates. These exudates constitute an important and constant carbon source that selects microbial populations in the plant rhizosphere, modifying global as well as specific microbial activities. We conducted an experiment in two-compartment devices to show the selection of bacterial communities by root exudates and phenanthrene as a function of distance to roots. Using direct DNA extraction, PCR amplification, and thermal gradient gel electrophoresis screening, bacterial population profiles were analyzed in parallel to bacterial counts and quantification of phenanthrene biodegradation in three layers (0 to 3, 3 to 6, and 6 to 9 mm from root mat) of unplanted-polluted (phenanthrene), planted-polluted, and planted-unpolluted treatments. Bacterial community differed as a function of the distance to roots, in both the presence and the absence of phenanthrene. In the planted and polluted treatment, biodegradation rates showed a strong gradient with higher values near the roots. In the nonplanted treatment, bacterial communities were comparable in the three layers and phenanthrene biodegradation was high. Surprisingly, no biodegradation was detected in the section of planted polluted treatment farthest from the roots, where the bacterial community structure was similar to those of the nonplanted treatment. We conclude that root exudates and phenanthrene induce modifications of bacterial communities in polluted environments and spatially modify the activity of degrading bacteria.     

Physical and Biological Treatment of Oil-Contaminated Soil in a Baffled Roller Bioreactor

Physical and biological removal of diesel oil from contaminated soil was studied in a baffled roller bioreactor. Initially, the effects of four factors (soil loading, temperature, pH, and surfactant) on physical removal of diesel oil were investigated. Only the presence of a surfactant (sodium dodecyl sulfate [SDS]) demonstrated a significant effect on diesel oil removal. Diesel oil removal efficiency was increased from 32.0% to 63.9% in the presence of 100 mg/L SDS. Using a microbial culture enriched from contaminated soil, biological treatment of diesel oil polluted soil under different soil loadings (15% to 50%), different diesel oil concentrations (1 to 50 g/L), and different types of soil (sand, silt, and clay) was then investigated in the baffled roller bioreactor. Biodegradation consisted of both fast and slow stages for degradation of light and heavy compounds, respectively. All biodegradation experiments demonstrated significant decreases in diesel oil concentrations (88.3% in 14 days for initial diesel oil concentrations of 1000 mg/L and a wide range of soil loadings). The presence of silty or sandy soils enhanced the biodegradation rate compared to the control bioreactor (without soil). The sandy soil loading had no effect on the biodegradation results. Using the enriched culture, the baffled roller bioreactor was able to biodegrade high diesel concentrations (up to 50 g/L) with biodegradation rates of 112.2 and 39.3 mg/L· h during fast and slow stages, respectively.     

Identification and biodegradation efficiency of a newly isolated 2,2′,4,4′-tetrabromodiphenyl ether (BDE-47) aerobic degrading bacterial strain

Polybrominated diphenyl ethers (PBDEs) are bioaccumulative, toxic and persistent, globally distributed organic chemicals in environment. However, very little is known for their aerobic biodegradation. In this research, 2,2′,4,4′-tetrabromodiphenyl ether (BDE-47) was selected as a model congener of PBDEs to study its aerobic biodegradation. A new BDE-47 degrading strain BFR01 identified as Pseudomonas stutzeri was isolated from polluted soil in a former brominated flame retardant production corporation. Stain BFR01 could utilize BDE-47 as a sole source of carbon and energy, and transformed 97.94% of BDE-47 in two weeks; the biodegradation of BDE-47 fitted well with the first-order kinetics, with the first-order kinetics constant of 0.32 d⁻¹. The biodegradation efficiency of stain BFR01 was higher than other reported PBDEs aerobic degrading bacteria. The biodegradation efficiency achieved maximum at pH 7.0 and 40 °C. The presence of additional carbon sources could enhance the biodegradation efficiency of BDE-47 by 1–6%. Furthermore, no lower brominated diphenyl ethers or biphenyl were detected, suggesting that the pathway of BDE-47 biodegradation by strain BFR01 might not be debromination with lower brominated diphenyl ethers as products. This is the first report of aerobic degradation of BDE-47 by P. stutzeri.     

Link between spatial structure of microbial communities and degradation of a complex mixture of volatile organic compounds in peat biofilters

AIMS: To investigate the relationships between the operation of the volatile organic compound (VOC) removal biofilter and the structure of microbial communities, and to study the impact on degradation activities and the structuring of microbial communities of biofilter malfunctions related to the qualitative composition of the polluted air. METHODS AND RESULTS: A microbiological study and a measurement of biodegradation activities were simultaneously carried out on two identical peat-packed columns, seeded with two different inocula, treating polluted air containing 11 VOCs. For both reactors, the spatial structure of the microbial communities was investigated by means of single-strand conformation polymorphism (SSCP) analysis. For both reactors, stratification of degradation activities in function of depth was observed. Oxygenated compounds were removed at the top of the column and aromatics at the bottom. Comparison of SSCP patterns clearly showed a shift in community structure in function of depth inside both biofilters. This distribution of biodegradation activities correlates with the spatialization of microbial density and diversity. Although the operating conditions of both reactors were identical and the biodegradation activities similar, the composition of microflora differed for biofilters A and B. Subdivision of biofilter B into two independent parts supplied with polluted air containing the complex VOC mixture showed that the microflora having colonized the bottom of biofilter B retained their potential for degrading oxygenated compounds. CONCLUSIONS: This work highlights the spatialization of biodegradation functions in a biofilter treating a complex mixture of VOCs. This distribution of biodegradation activities correlates with the spatialization of microbial density and diversity. SIGNIFICANCE AND IMPACT OF THE STUDY: This vertical structure of microbial communities must be taken into consideration when dealing with the malfunctioning of bioreactors. These results are also useful information about changes in microbial communities following natural or anthropogenic alterations in different ecosystems (soils and sediments) where structuring of microbial communities according to depth has been observed.     

Toward the bioremediation of dioxin-polluted soil: structural and functional analyses of in situ microbial populations by quinone profiling and culture-dependent methods

In order to obtain basic information toward the bioremediation of dioxin-polluted soil, microbial communities in farmland soils polluted with high concentrations of polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs) were studied by quinone profiling as well as conventional microbiological methods. The concentration of PCDD/Fs in the polluted soils ranged from 36 to 4,980 pg toxicity equivalent quality (TEQ) g(-1) dry weight of soil. There was an inverse relationship between the levels of PCDD/Fs and microbial biomass as measured by direct cell counting and quinone profiling. The most abundant quinone type detected was either MK-6 or Q-10. In addition, MK-8, MK-8(H2), and MK-9(H8) were detected in significant amounts. Numerical analysis of quinone profiles showed that the heavily polluted soils (> or = 1,430 pg TEQ g(-1)) contained different community structures from lightly polluted soils (< or = 56 pg TEQ g(-1)). Cultivation of the microbial populations in the heavily polluted soils with dibenzofuran or 2-chlorodibenzofuran resulted in enrichment of Q-10-containing bacteria. When the heavily polluted soil was incubated in static bottles with autoclaved compost as an organic nutrient additive, the concentrations of PCDD/Fs in the soil were decreased by 22% after 3 months of incubation. These results indicate that dioxin pollution exerted a significant effect on microbial populations in soil in terms of quantity, quality, and activity. The in situ microbial populations in the dioxin-polluted soil were suggested to have a potential for the transformation of PCDD/Fs and oxidative degradation of the lower chlorinated ones thus produced.     

Methylotrophic extremophilic yeast Trichosporon sp.: a soil-derived isolate with potential applications in environmental biotechnology

A yeast isolate revealing unique enzymatic activities and substrate-dependent polymorphism was obtained from autochthonous microflora of soil heavily polluted with oily slurries. By means of standard yeast identification procedures the strain was identified as Trichosporon cutaneum. Further molecular PCR product analyses of ribosomal DNA confirmed the identity of the isolate with the genus Trichosporon. As it grew on methanol as a sole carbon source, the strain appeared to be methylotrophic. Furthermore, it was also able to utilize formaldehyde. A multi-substrate growth potential was shown with several other carbon sources: glucose, glycerol, ethanol as well as petroleum derivatives and phenol. Optimum growth temperature was determined at 25 degrees C, and strong inhibition of growth at 37 degrees C together with the original soil habitat indicated lack of pathogenicity in warm-blooded animals and humans. The unusually high tolerance to xenobiotics such as diesel oil (>30 g/l), methanol (50 g/l), phenol (2 g/l) and formaldehyde (7.5 g/l) proved that the isolate was an extremophilic organism. With high-density cultures, formaldehyde was totally removed at initial concentrations up to 7.5 g/l within 24 h, which is the highest biodegradation capability ever reported. Partial biodegradation of methanol (13 g/l) and diesel fuel (20 g/l) was also observed. Enzymatic studies revealed atypical methylotrophic pathway reactions, lacking alcohol oxidase, as compared with the conventional methylotroph Hansenula polymorpha. However, the activities of glutathione-dependent formaldehyde dehydrogenase, formaldehyde reductase, formate dehydrogenase and unspecific aldehyde dehydrogenase(s) were present. An additional glutathione-dependent aldehyde dehydrogenase activity was also detected. Metabolic and biochemical characteristics of the isolated yeast open up new possibilities for environmental biotechnology. Some potential applications in soil bioremediation and wastewater decontamination are discussed.     

Effect of iron on the biodegradation of petroleum in seawater.

The biodegradation of South Louisiana (SL) crude oil and the effects of nitrogen, phosphorus, and iron supplements on this process were compared in a polluted (10,900 oil degraders per liter) and in a relatively clean (750 oil degraders per liter) littoral seawater sample taken along the New Jersey coast. Without supplements, the biodegradation of SL crude oil was negligible in both seawater samples. Addition of nitrogen and phosphorus allowed very rapid biodegradation (72% in 3 days) in polluted seawater. Total iron in this seawater sample was high (5.2 muM), and the addition of iron did not increase the biodegradation rate further. In the less polluted and less iron-rich (1.2 muM) seawater sample, biodegradation of SL crude oil was considerably slower (21% in 3 days) and the addition of chelated iron had a stimulating effect. Ferric octoate was shown to have a similar stimulating effect on SL crude oil biodegradation as chelated iron. Ferric octoate, in combination with paraffinized urea and octylphosphate, is suitable for treatment of floating oil slicks. We conclude that spills of SL crude and similar oils can be cleaned up rapidly and efficiently by stimulated biodegradation, provided the water temperatures are favorable.     

Microbial degradation of street dust polycyclic aromatic hydrocarbons in microcosms simulating diffuse pollution of urban soil

Diffuse pollution with polycyclic aromatic hydrocarbons (PAHs) of topsoil in urban regions has caused increasing concerns in recent years. We simulated diffuse pollution of soil in microcosms by spiking sandy topsoil (A-horizon) and coarse, mineral subsoil (C-horizon) with street dust (PM63) isolated from municipal street sweepings from central Copenhagen. The microbial communities adapted to PAH degradation in microcosms spiked with street dust in both A-horizon and C-horizon soils, in spite of low PAH-concentrations. The increased potential for PAH degradation was demonstrated on several levels: by slowly diminishing PAH-concentrations, increased mineralization of 14C-PAHs, increasing numbers of PAH degraders and increased prevalence of nah and pdo1 PAH degradation genes, i.e. the microbial communities quickly adapted to PAH degradation. Three- and 4-ring PAHs from the street dust were biodegraded to some extent (10-20%), but 5- and 6-ring PAHs were not biodegraded in spite of frequent soil mixing and high PAH degradation potentials. In addition to biodegradation, leaching of 2-, 3- and 4-ring PAHs from the A-horizon to the C-horizon seems to reduce PAH-levels in surface soil. Over time, levels of 2-, 3- and 4-ring PAHs in surface soil may reach equilibrium between input and the combination of biodegradation and leaching. However, levels of the environmentally critical 5- and 6-ring PAHs will probably continue to rise. We presume that sorption to black carbon particles is responsible for the persistence and low bioaccessibility of 5- and 6-ring PAHs in diffusely polluted soil.     

The effects of carbon sources and micronutrients in fermented whey on the biodegradation of n-hexadecane in diesel fuel contaminated soil

Fermented whey has previously been shown to stimulate biodegradation of n-hexadecane in diesel contaminated soils. The proposed explanation for the stimulatory effect is that fermented whey provides easily accessible carbon and micronutrients, which give rise to an increased degrading biomass.The objective of this work has been to investigate the role of the different carbon sources and vitamins in fermented whey on the microbial degradation of n-hexadecane in soil.The effects of lactose, lactate, vitamins and free amino acids were tested in combinations according to a full factorial design experiment, at concentrations corresponding to those present in fermented whey. The target substance was ¹⁴C-labeled n-hexadecane in nutrient amended soil microcosms contaminated with 5000 mg diesel fuel kg⁻¹ dw. Biodegradation was monitored by determination of evolved ¹⁴CO₂.Significant effects on the biodegradation of n-hexadecane were observed for lactate and amino acids additions in a sandy soil. Lactate showed both an inhibitory effect in the early phase of the experiment and a stimulatory effect in the later phase. The effect of amino acids was slightly stimulatory, mainly evident as a shortening of the lag time.The degree of n-hexadecane degradation at the end of the experiment was correlated with the total concentration of organic compounds added to the soil.Scientific relevanceThere are a handful papers describing the potential of using organic amendments (often industrial by-products) with a content of both easily accessible carbon and micronutrients, to enhance the bioremediation of polluted soils. Enhanced biodegradation is often reported and the proposed explanations are that the combination of easily accessible carbon and micronutrients increases the degrading biomass.In this paper, we examine the effect of fermented whey on the degradation of n-hexadecane and correlate the observed effects on the biodegradation with the main components lactate, amino acids, lactose and B-vitamins. This has to our knowledge never been done before.     

The effects of carbon sources and micronutrients in fermented whey on the biodegradation of n-hexadecane in diesel fuel contaminated soil

Fermented whey has previously been shown to stimulate biodegradation of n-hexadecane in diesel contaminated soils. The proposed explanation for the stimulatory effect is that fermented whey provides easily accessible carbon and micronutrients, which give rise to an increased degrading biomass.The objective of this work has been to investigate the role of the different carbon sources and vitamins in fermented whey on the microbial degradation of n-hexadecane in soil.The effects of lactose, lactate, vitamins and free amino acids were tested in combinations according to a full factorial design experiment, at concentrations corresponding to those present in fermented whey. The target substance was ¹⁴C-labeled n-hexadecane in nutrient amended soil microcosms contaminated with 5000 mg diesel fuel kg⁻¹ dw. Biodegradation was monitored by determination of evolved ¹⁴CO₂.Significant effects on the biodegradation of n-hexadecane were observed for lactate and amino acids additions in a sandy soil. Lactate showed both an inhibitory effect in the early phase of the experiment and a stimulatory effect in the later phase. The effect of amino acids was slightly stimulatory, mainly evident as a shortening of the lag time.The degree of n-hexadecane degradation at the end of the experiment was correlated with the total concentration of organic compounds added to the soil.

Scientific relevance

There are a handful papers describing the potential of using organic amendments (often industrial by-products) with a content of both easily accessible carbon and micronutrients, to enhance the bioremediation of polluted soils. Enhanced biodegradation is often reported and the proposed explanations are that the combination of easily accessible carbon and micronutrients increases the degrading biomass.In this paper, we examine the effect of fermented whey on the degradation of n-hexadecane and correlate the observed effects on the biodegradation with the main components lactate, amino acids, lactose and B-vitamins. This has to our knowledge never been done before.     

Incorporation of Petroleum Carbon Into Soil Organic Matter During Biodegradation

A procedure, based on measurement of the stable carbon isotope ¹³C, has been developed for determining the extent to which petroleum carbon is incorporated into soil organic matter (SOM) by humification of biomass produced during biodegradation of the petroleum in soil. We have shown that a crude oil having a δ¹³C of-27.4%, when biodegraded in a soil containing SOM with a δ¹³C of-15.7%, resulted in a change of the δ¹³C of the bound SOM reflecting that of petroleum carbon. Comparison of five soil biodegradation tests using different amounts and types of fertilizer to stimulate biodegradation of the oil in this soil showed that the extent of the δ¹³C change in the bound SOM varied with the extent of oil biodegradation observed. To obtain ¹³C data on the SOM, the residual petroleum was first removed by rigorous extraction with dichloromethane using a Soxhlet apparatus. The extracted soil was then combusted to release bound carbon as CO₂, which was analyzed for ¹³C. Where the SOM has a δ¹³C similar to that of petroleum, ¹⁴C measurements of SOM would give similar results. This type of data, referred to as the petroleum “footprint” in the SOM, could be useful in identifying or confirming intrinsic biodegradation of petroleum in contaminated soil.     

转Bt水稻对土壤可溶性有机碳氮及微生物学性质的影响

研究了3种转Bt水稻［克螟稻（KMD）、华恢1号（HH1）和Bt汕优63（BtSY63）］及对应亲本在2年大田条件下对土壤可溶性有机碳（DOC）和可溶性有机氮（DON）及微生物学性质的影响.结果表明：测定指标均随采样时间发生显著变化.与对应亲本相比,转Bt水稻对土壤DOC、DON和微生物生物量氮（MBN）的影响不显著,而对土壤微生物生物量碳（MBC）、基础呼吸（BR）和微生物代谢熵（qCO₂）的影响在大田种植第1年某些时段达到显著水平（P<0.05）,但这种影响没有持续到第2年;3种亲本水稻土壤DOC、DON及微生物学性质差异均不显著,但相应转Bt水稻土壤MBC、BR、qCO₂差异显著,BtSY63土壤MBC和BR显著高于KMD及HH1,而qCO₂显著低于KMD及HH1.转Bt水稻2年的大田种植对土壤DOC和DON及微生物学性质的影响较小,但3种转Bt水稻之间微生物学性质的差异比亲本之间的差异大,表明长期监测可能有助于发现转Bt水稻对土壤生态系统结构和功能的影响.     

Biodegradation of benzene, toluene and naphthalene in soil-water slurry microcosms

Aerobic biodegradation of benzene, toluene andnaphthalene was studied in pre-equilibrated soil-waterslurry microcosms. The experiments were designed tosimulate biodegradation at waste sites where sorptionreaches equilibrium before biodegradation becomesimportant. Rates of biodegradation were reduced by thepresence of soil. For example, nearly completenaphthalene biodegradation (1.28 mg/L) by indigenoussoil bacteria occurred within 60 hours in aqueoussolution (soil-free) while it took two weeks todegrade the same amount in the presence of 0.47 kgsoil/L of water. The rate of biodegradation wasobserved to decrease with increasing organic compoundhydrophobicity, soil/water ratio, soil particle size,and soil organic carbon content. These resultsclearly indicate that the rate of biodegradation isaffected by both the extent and rate of sorption. Further analysis suggests that mass transfer couldcontrol the performance of in situ bioremediation forhighly hydrophobic organic contaminants which exhibita large extent of sorption and slow rate ofdesorption.     

Aerobic biomineralization of alpha-hexachlorocyclohexane in contaminated soil

The factors identified to be important for the aerobic biodegradation of alpha-hexachlorocyclohexane (alpha-HCH) in a soil slurry are temperature, auxiliary carbon source, substrate concentration, and soil inhomogeneities. Temperatures in the range of 20 to 30 degrees C were determined to be most favorable for biodegradation of alpha-HCH. No alpha-HCH biodegradation was detected at temperatures below 4 degrees C and above 40 degrees C. The addition of auxiliary organic carbon compounds showed repressive effects on alpha-HCH biomineralization. Increased oxygen partial pressures reduced the repressive effects of added auxiliary organic carbon compounds. A linear relationship between alpha-HCH concentration and its conversion rate was found in a Lineweaver-Burk plot. Inhomogeneities such as clumping of alpha-HCH significantly affected its biodegradation. Inhomogeneity as an influence on biodegradation has not drawn sufficient attention in the past, even though it certainly has affected both laboratory studies and the application of biotechnological methods to clean up contaminated sites. On the basis of metabolites detected during degradation experiments, the initial steps of aerobic alpha-HCH bioconversion in a soil slurry are proposed.     

Assessment of biological activity and fate of organic compounds in a reactor for the measurement of biodegradable organic carbon in water

A new, rapid method for the determination of biodegradable dissolved organic carbon (BDOC), especially suited to water industry needs, was recently proposed by the authors. This dynamic method measured the BDOC of circulating water continuously pumped over a biofilm attached to a special support (sinterized porous glass) that fills a system of two glass columns. The BDOC value corresponds to the difference in dissolved organic carbon (DOC) between inflow and outflow water samples. The analytical results are not significantly different from those of other bioassays that use indigenous bacteria, and the total duration of the analysis is less than 3 h. However, a problem common to all the BDOC methods based on attached bacteria is the extent to which the decrease in DOC during the BDOC analysis is due to true biodegradation or to adsorption of organic matter to the reactor. In the present study, a reasonable support is provided for the hypothesis that this decrease, at least in the dynamic method, is predominantly due to microbiological activity. After comparing the support (sinterized porous glass) with a good physical adsorbent (granular activated carbon), the influence of temperature, residual chlorine and sodium azide on the reactor performance was tested, and a sensitivity only attributable to biological activity was observed. Another set of experiments were performed to assess the fate and specific elimination of different organic substances, explicable assuming that biodegradation processes were involved.     

Aerobic biomineralization of alpha-hexachlorocyclohexane in contaminated soil.

The factors identified to be important for the aerobic biodegradation of alpha-hexachlorocyclohexane (alpha-HCH) in a soil slurry are temperature, auxiliary carbon source, substrate concentration, and soil inhomogeneities. Temperatures in the range of 20 to 30 degrees C were determined to be most favorable for biodegradation of alpha-HCH. No alpha-HCH biodegradation was detected at temperatures below 4 degrees C and above 40 degrees C. The addition of auxiliary organic carbon compounds showed repressive effects on alpha-HCH biomineralization. Increased oxygen partial pressures reduced the repressive effects of added auxiliary organic carbon compounds. A linear relationship between alpha-HCH concentration and its conversion rate was found in a Lineweaver-Burk plot. Inhomogeneities such as clumping of alpha-HCH significantly affected its biodegradation. Inhomogeneity as an influence on biodegradation has not drawn sufficient attention in the past, even though it certainly has affected both laboratory studies and the application of biotechnological methods to clean up contaminated sites. On the basis of metabolites detected during degradation experiments, the initial steps of aerobic alpha-HCH bioconversion in a soil slurry are proposed.