Anthracene biodegradation under nitrate-reducing condition and associated microbial community changes

Anaerobic biodegradation of polycyclic aromatic hydrocarbons (PAHs) and degraders in the subsurface environment have aroused increasing attention. Molecular techniques are especially useful when isolates are hard to obtain. Nitrate-reducing microcosms inoculated with aquifer sediment were constructed to investigate anthracene biodegradation. The associated microbial community changes were characterized using terminal restriction fragment length polymorphism analysis (TRFLP) in combination with 16S rRNA gene clone library analysis. A nearly complete removal of anthracene was achieved after an eighty day incubation under the nitrate-reducing condition. The two molecular techniques revealed a significant shift of microbial community structure, coupled with anthracene biodegradation. Species of genera Paracoccus, Herbaspirillum, Azotobacter, and Rhodococcus were grouped into four major operational taxonomic units (OTUs) in the library that was constructed with the microcosm sample on day 80. The enrichment of these genera might have links to anthracene biodegradation under the nitrate-reducing condition. Microbial consortia likely played a part in anthracene degradation.     

Enhanced biodegradation of methoxychlor in soil under sequential environmental conditions.

Ring-U-[14C]methoxychlor [1,1-bis(p-methoxyphenyl)-2,2,2-trichloroethane] was incubated in soil under aerobic and anaerobic conditions. Primary degradation of methoxychlor occurred under anaerobic conditions, but not under aerobic conditions, after 3 months of incubation. Analysis of soil extracts, using gas chromatography, demonstrated that only 10% of the compound remained at initial concentrations of 10 and 100 ppm (wt/wt) of methoxychlor. Evidence is presented that a dechlorination reaction was responsible for primary degradation of methoxychlor. Analysis of soils treated with 100 ppm of methoxychlor in the presence of 2% HgCl2 showed that 100% of the compound remained after 3 months, indicating that degradation in the unpoisoned flasks was biologically mediated. Methanogenic organisms, however, are probably not involved, as strong inhibition of methane production was observed in all soils treated with methoxychlor. During the 3-month incubation period, little or no evaluation of 14CO2 or 14CH4 occurred under either aerobic or anaerobic conditions. Cometabolic processes may be responsible for the extensive molecular changes which occurred with methoxychlor because the rate of its disappearance from soil was observed to level off after exhaustion of soil organic matter. After this incubation period, soils previously incubated under anaerobic conditions were converted to aerobic conditions. The rates of 14CO2 evolution from soils exposed to anaerobic and aerobic sequences of environments ranged from 10- to 70-fold greater than that observed for soils exposed solely to an aerobic environment.     

Accelerated biodegradation of cured cement paste by Thiobacillus species under simulation condition

Biodegradation is one of the most important types of cement deterioration. Complex microbial populations take part in the biodegradation process of cement-based materials. Studies in this field show that the sulfur-oxidizing bacteria, including Acidithiobacillus thiooxidans, due to sulfuric acid formation, play a key role in this process. In this study, with the accelerated leaching process of calcium hydroxide of cement paste, cured under running tap water and exposed to sterile biogenic sulfuric acid for 6 days, the surface pH of the cement was reduced to a more favorable level for bacterial growth. In this case, the growth of Thiobacillus proceeded in the presence of cured cement paste specimens. After 90 days of exposure to a semi-continuous culture of A. thiooxidans with its pH less than 2 and continuous removal of damaged layers the compressive strength, length and mass of the samples dropped by 96%, 11% and 43%, in the order given. The mechanism of degradation and the structure of degraded specimens were analyzed by test laboratory techniques such as, XRD, SEM and EDAX analyses.     

Anaerobic biodegradation of ethylthionocarbamate by the mixed bacteria under various electron acceptor conditions

Biodegradation behavior and kinetics of ethylthionocarbamate under nitrate, sulfate and ferric reducing conditions by mixed cultures enriched from the anaerobic digester sludge was investigated. The results showed that ethylthionocarbamate could be degraded independently by the mixed cultures coupled to nitrate, sulfate, and ferric reduction, and meanwhile, nitrite, sulfide, and ferrous were accumulated as a result of nitrate, sulfate and ferric reduction, respectively. Ferric was a more favorable terminal electron acceptor compared to nitrate and sulfate. The order of the electron acceptors with decreasing biodegradation rates of the ethylthionocarbamate was: ferric>nitrate>sulfate, and the corresponding maximum biodegradation rate was 7.240, 6.267, and 4.602 mg/(L·d), respectively. The anaerobic biodegradation of ethylthionocarbamate under various electron acceptor conditions can be accurately described by first order exponential decay kinetics.     

Enhanced biodegradation of a hard bis-quaternary ammonium salt

Bacterial strains with a high biodegradation potential were isolated from activated sludge. Their ability to decompose the hard bis-quaternary ammonium salt FB was determined by the method of chemical oxygen demand (COD) in a mineral medium, where the compound FB was the only source of carbon. The COD values were very low after 21 d and in the course of this period they reached zero level twice. The contribution of adsorption to decrease the COD value was small. The maximum COD decrease was accompanied by an increase of cell respiration. It is suggested that FB is effectively decomposed in spite of the fact that according to its structure it is a typical hard detergent.     

Enhanced condition in dogwhelks, Nucella lapillus (L.) living under mussel hummocks

Dogwhelks, Nucella lapillus eat both barnacles and mussels, Mytilus edulis. However, mussels are dangerous prey because they can snare and immobilize dogwhelks with their byssi. Despite this danger, adult dogwhelks are common inside mussel hummocks or stacks found on mature mussel beds. The whelks live in debris-filled chambers within the hummocks, unsnared by byssi. Evidence is presented to show that this is a highly favourable microhabitat for dogwhelks. Condition index (CI) measurements showed that mean CI for “hummock” dogwhelks was 20.99 in early spring, 29.65 in midsummer and 34.86 in early winter. In comparison, CI values for dogwhelks from nearby barnacle zones were 20.13, 25.03 and 24.66 respectively. The summer and winter CI values of “hummock” dogwhelks were enhanced to a highly significant extent. Data are also presented to show that shore elevation or dogwhelk shell height (over the size range of animals studied) had no confounding effect on this result. Predicted flesh and shell mass values for a standard 25 mm high whelk showed that occupation of hummocks was associated with a thin-walled shell morphology, and that the shell mass became proportionately lower in summer and early winter. A feeding experiment showed that CI rises slowly, even in dogwhelks fed to satiation on mussels. Dogwhelks were taken from the barnacle zone in March 1997 and either fed to satiation on Mytilus or starved, whilst being held in seawater at ambient seawater temperature. The CI of fed dogwhelks rose from 19.7 to 27.4 in 3 months, while that of starved Nucella fell from 19.7 to 16.3. In the meantime, the CI of dogwhelks in situ in the barnacle zone had risen from 19.7 to 23.8. Hence, 3 months' satiation ration had led to a nett 3.6 unit rise in CI; starvation to a nett 7.5 unit fall. All of the changes in CI were due to changes in flesh mass; shell mass was stable. Since “hummock” dogwhelks collected in early winter have a CI value about 10.2 units greater than barnacle zone dogwhelks, this indicates that “hummock” dogwhelks are long-term inhabitants of this microhabitat.     

Enhanced biodegradation of hexachlorocyclohexane (HCH) in contaminated soils via inoculation with Sphingobium indicum B90A

Soil pollution with hexachlorocyclohexane (HCH) has caused serious environmental problems. Here we describe the targeted degradation of all HCH isomers by applying the aerobic bacterium Sphingobium indicum B90A. In particular, we examined possibilities for large-scale cultivation of strain B90A, tested immobilization, storage and inoculation procedures, and determined the survival and HCH-degradation activity of inoculated cells in soil. Optimal growth of strain B90A was achieved in glucose-containing mineral medium and up to 65% culturability could be maintained after 60 days storage at 30°C by mixing cells with sterile dry corncob powder. B90A biomass produced in water supplemented with sugarcane molasses and immobilized on corncob powder retained 15–20% culturability after 30 days storage at 30°C, whereas full culturability was maintained when cells were stored frozen at −20°C. On the contrary, cells stored on corncob degraded γ-HCH faster than those that had been stored frozen, with between 15 and 85% of γ-HCH disappearance in microcosms within 20 h at 30°C. Soil microcosm tests at 25°C confirmed complete mineralization of [¹⁴C]-γ-HCH by corncob-immobilized strain B90A. Experiments conducted in small pits and at an HCH-contaminated agricultural site resulted in between 85 and 95% HCH degradation by strain B90A applied via corncob, depending on the type of HCH isomer and even at residual HCH concentrations. Up to 20% of the inoculated B90A cells survived under field conditions after 8 days and could be traced among other soil microorganisms by a combination of natural antibiotic resistance properties, unique pigmentation and PCR amplification of the linA genes. Neither the addition of corncob nor of corncob immobilized B90A did measurably change the microbial community structure as determined by T-RFLP analysis. Overall, these results indicate that on-site aerobic bioremediation of HCH exploiting the biodegradation activity of S. indicum B90A cells stored on corncob powder is a promising technology.     

Enhanced octadecane dispersion and biodegradation by a Pseudomonas rhamnolipid surfactant (biosurfactant).

A microbial surfactant (biosurfactant) was investigated for its potential to enhance bioavailability and, hence, the biodegradation of octadecane. The rhamnolipid biosurfactant used in this study was extracted from culture supernatants after growth of Pseudomonas aeruginosa ATCC 9027 in phosphate-limited proteose peptone-glucose-ammonium salts medium. Dispersion of octadecane in aqueous solutions was dramatically enhanced by 300 mg of the rhamnolipid biosurfactant per liter, increasing by a factor of more than 4 orders of magnitude, from 0.009 to > 250 mg/liter. The relative enhancement of octadecane dispersion was much greater at low rhamnolipid concentrations than at high concentrations. Rhamnolipid-enhanced octadecane dispersion was found to be dependent on pH and shaking speed. Biodegradation experiments done with an initial octadecane concentration of 1,500 mg/liter showed that 20% of the octadecane was mineralized in 84 h in the presence of 300 mg of rhamnolipid per liter, compared with only 5% octadecane mineralization when no surfactant was present. These results indicate that rhamnolipids may have potential for facilitating the bioremediation of sites contaminated with hydrocarbons having limited water solubility.     

Enhanced biodegradation of phenanthrene in a biphasic culture system

Degradation of phenanthrene byPseudomonas aeruginosa AK1 was examined in (i) an aqueous mineral salts medium to which phenanthrene particles of varying size (i.e. diameter) were added, and (ii) an aqueous/organic biphasic culture system consisting of mineral salts medium supplemented with 2,2,4,4,6,8,8-heptamethylnonane (HMN) as the phenanthrene-carrying organic phase. In both systems, the rate of phenanthrene biodegradation could be significantly enhanced by manipulations leading to improved phenanthrene mass transfer into the aqueous phase. With crystalline phenanthrene, the rate of biodegradation was found to be directly correlated to the particle surface area, whereas in the biphasic system the rate of biodegradation of the dissolved phenanthrene was mainly governed by the HMN/water interface area. In the latter system, exponential growth with a doubling time t _d of 6–8 hours has been achieved under conditions of intensive agitation of the medium indicating that phenanthrene degradation by strain AK1 is limited mainly by physicochemical parameters. Addition of selected surfactants to the culture medium was found to accelerate phenanthrene degradation by strain AK1 only under conditions of low agitation (in the presence of HMN) and after pretreatment of phenanthrene crystals by ultrasonication (in the absence of HMN). Evidence is presented that the stimulating effect of the surfactants was primarily due to improved dispersion of phenanthrene particle agglomerates (in the aqueous mineral salts medium supplemented with phenanthrene crystals) or of the phenanthrene-carrying lipophilic solvent drops (in the aqueous/organic biphasic culture system) whereas the solubilizing activity towards phenanthrene was neglectible. Under conditions of intensive mixing of the culture medium (i.e. if a high particle surface area or HMN/water interface area, respectively, is provided), the addition of surfactants did not enhance phenanthrene biodegradation.     

Enhanced Biodegradation and Fate of Hexahydro-1,3,5-Trinitro-1,3,5-Triazine (RDX) and Octahydro-1,3,5,7-Tetranitro-1,3,5,7-Tetrazocine (HMX) in Anaerobic Soil Slurry Bioprocess

Native soil microbial populations and unadapted municipal anaerobic sludges were compared for nitramine explosive degradation in microcosm assays under various conditions. Microbial populations from an explosive-contaminated soil were only able to mineralize 12% hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) (at a concentration of 800 mg/kg slurry) or 4% octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX) (at a concentration of 267 mg/kg slurry). In contrast, municipal anaerobic sludges were able to mineralize them to carbon dioxide, with efficiencies of up to 65%. Reduction of RDX and HMX into their corresponding nitroso-derivatives was notably faster than their mineralization. The biodegradation of HMX was typically delayed by the presence of RDX in the microcosm, confirming RDX is used as an electron acceptor preferentially to HMX. The laboratory-scale bioslurry reactor reproduced the results of the microcosm assays, yet with much higher RDX and HMX degradation rates. A radiolabel-based mass balance in the soil slurry indicated that, besides a significant mineralization to carbon dioxide, 25% and 31% of RDX and HMX, respectively, appeared as acetonitrile-extractable metabolites, while the remaining part was incorporated into biomass and irreversibly bound to the soil matrix. About 10% of the HMX derivatives were estimated to be chemically bound to the soil matrix, while for RDX the estimation was nil.     

Biodegradability and biodegradation of poly(lactide)

Poly(lactide) (PLA) has been developed and made commercially available in recent years. One of the major tasks to be taken before the widespread application of PLA is the fundamental understanding of its biodegradation mechanisms. This paper provides a short overview on the biodegradability and biodegradation of PLA. Emphasis is focused mainly on microbial and enzymatic degradation. Most of the PLA-degrading microorganisms phylogenetically belong to the family of Pseudonocardiaceae and related genera such as Amycolatopsis, Lentzea, Kibdelosporangium, Streptoalloteichus, and Saccharothrix. Several proteinous materials such as silk fibroin, elastin, gelatin, and some peptides and amino acids were found to stimulate the production of enzymes from PLA-degrading microorganisms. In addition to proteinase K from Tritirachium album, subtilisin, a microbial serine protease and some mammalian serine proteases such as α-chymotrypsin, trypsin, and elastase could also degrade PLA.     

Enhanced anaerobic biodegradation of benzene-toluene-ethylbenzene-xylene-ethanol mixtures in bioaugmented aquifer columns

Methanogenic flowthrough aquifer columns were used to investigate the potential of bioaugmentation to enhance anaerobic benzene-toluene-ethylbenzene-xylene (BTEX) degradation in groundwater contaminated with ethanol-blended gasoline. Two different methanogenic consortia (enriched with benzene or toluene and o-xylene) were used as inocula. Toluene was the only hydrocarbon degraded within 3 years in columns that were not bioaugmented, although anaerobic toluene degradation was observed after only 2 years of acclimation. Significant benzene biodegradation (up to 88%) was observed only in a column bioaugmented with the benzene-enriched methanogenic consortium, and this removal efficiency was sustained for 1 year with no significant decrease in permeability due to bioaugmentation. Benzene removal was hindered by the presence of toluene, which is a more labile substrate under anaerobic conditions. Real-time quantitative PCR analysis showed that the highest numbers of bssA gene copies (coding for benzylsuccinate synthase) occurred in aquifer samples exhibiting the highest rate of toluene degradation, which suggests that this gene could be a useful biomarker for environmental forensic analysis of anaerobic toluene bioremediation potential. bssA continued to be detected in the columns 1 year after column feeding ceased, indicating the robustness of the added catabolic potential. Overall, these results suggest that anaerobic bioaugmentation might enhance the natural attenuation of BTEX in groundwater contaminated with ethanol-blended gasoline, although field trials would be needed to demonstrate its feasibility. This approach may be especially attractive for removing benzene, which is the most toxic and commonly the most persistent BTEX compound under anaerobic conditions.     

The impact of feed composition on biodegradation of benzoate under cyclic (aerobic/anoxic) conditions

The response of a mixed microbial culture to different feed compositions, that is, containing benzoate and pyruvate as sole carbon sources at different levels, was studied in a chemostat with a 48-h hydraulic residence time under cyclic aerobic and anoxic (denitrifying) conditions. The cyclic bacterial culture was well adapted to different feed compositions as evidenced by the lack of accumulation of benzoate or pyruvate in the chemostat. Both the benzoate-degrading capabilities and the in vitro catechol 2,3-dioxygenase (C23DO) activities of the cyclic bacterial cultures were in direct proportion to the flux through the chemostat of the substrate degraded by the pathway containing C23DO, with some exceptions. The quantity of C23DO showed a transient decrease during the initial portion of the aerobic period before returning to the level present during the anoxic period. That decrease was most likely caused by the production of H(2)O(2) by the cells upon being returned to aerobic conditions.     

Novel aspects of symbiotic (polyvinyl alcohol) biodegradation

A new polyvinyl alcohol (PVA)-degrading bacterium was isolated from activated sludge sampled during a waste water treatment process and identified as Sphingomonas sp. Its PVA oxidase activity and alcohol dehydrogenase activity for various low-molecular-weight secondary alcohols were detected. Both activities were associated with cells of the degrader, and they were not extracellular. Under optimal conditions, the isolate was able to degrade 500 mg of PVA per litre in 2 weeks. The strain required pyrroloquinoline quinone (PQQ) and another growth factor, the later could be supplied by a co-isolated Rhodococcus erythropolis strain. The findings stressed the complex nature of environmental PVA degradation and proved that other factors different from PQQ could be important in symbiotic biodegradation of PVA with some sphingomonads.     

全氟辛烷磺酸生物降解研究进展

全氟化合物(perfluorinated compounds,PFCs)是碳氢类化合物及其衍生物中氢原子全部被氟原子取代后形成的一类化合物。全氟辛烷磺酸(perfluorooctane sulfonate,PFOS)是一种典型的全氟化合物,对于生物具有多方面的毒性。研究发现,PFOS广泛存在于环境中,造成了一定的污染,PFOS的降解成为亟待解决的问题。但是由于PFOS稳定性高,降解较为困难,尤其是在生物降解方面的研究较少。本文主要介绍了PFOS降解技术的发展现状以及存在的问题,并提出PFOS生物降解的可能途径。     

Anaerobic biodegradation of cyanide under methanogenic conditions

Upflow, anaerobic, fixed-bed, activated charcoal biotreatment columns capable of operating at free cyanide concentrations of greater than 100 mg liter-1 with a hydraulic retention time of less than 48 h were developed. Methanogenesis was maintained under a variety of feed medium conditions which included ethanol, phenol, or methanol as the primary reduced carbon source. Under optimal conditions, greater than 70% of the inflow free cyanide was removed in the first 30% of the column height. Strongly complexed cyanides were resistant to removal. Ammonia was the nitrogen end product of cyanide transformation. In cell material removed from the charcoal columns, [14C]bicarbonate was the major carbon end product of [14C]cyanide transformation.     

铜离子对混合菌群降解三氯乙烯的影响与机制分析

在三氯乙烯(TCE)胁迫条件下,从生活垃圾填埋场覆盖土中富集得到了可高效降解TCE的混合菌群SWA1。考察了铜离子浓度0-15μmol/L范围内混合菌群对TCE的降解,当铜离子浓度为0.03μmol/L时,降解速率最大为29.60 nmol/min,降解率达95.75%。此条件下的pmo A和mmo X表达量均达最大值,pmo A的相对表达量(4.22 E-03)比mmo X(9.30 E-06)和Lmp H(0)高3个数量级。在0-0.75μmol/L和1-15μmol/L两个铜离子浓度区间,分别出现了TCE降解峰值,高通量测序结果表明,甲基孢囊菌科Methylocystaceae的甲烷氧化菌为优势微生物。随着铜离子浓度提高,混合菌群SWA1生物多样性显著降低。铜离子浓度的变化影响了混合菌群的结构和活性,进而影响了TCE降解机制。当铜离子浓度为0.03μmol/L时,降解机制包括TCE直接降解和甲烷氧化菌共代谢降解。当铜离子浓度为5μmol/L时,降解率可达到84.75%。此时,降解机制包括TCE直接降解以及甲烷氧化菌和含苯酚羟化酶菌群的共代谢降解。     

Kinetics of sucrose conversion to fructo-oligosaccharides using enzyme (invertase) under free condition

The study reports the synthesis of fructo-oligosaccharide (FOS) from sucrose using invertase derived from Saccharomyces cerevisiae. The reaction was conducted in a batch mode under free enzyme condition. Fructo-oligosaccharide formation was detected at a high sucrose concentration of over 200 g/L. The investigation was extended to study the effect of different parameters such as initial sucrose concentration (ISC), pH, and enzyme concentration. A maximum FOS yield of 10 % (dry basis) was observed using 525 g/L of ISC, with 6 U/mL of the enzyme, and pH 5.5 at 40 °C. 1-Kestose was the major product of among different forms of FOS. The FOS yield increased with an increase in sucrose concentration up to 525 g/L, beyond which it started to decrease. However, the maximum FOS yield was not affected by the increasing concentration of the enzyme beyond a certain level (2 U/mL). Furthermore, the activity of enzyme slightly increased with an increase in the pH up to 6, and thereafter it declined. Addition of glucose decreased the FOS yield because of enzyme inhibition. A five-step, ten-parameter model was developed, for which the simulation was performed in COPASI. The results predicted by the model were consistent with the experimental data.     

Aerobic biodegradation of vinyl chloride by a highly enriched mixed culture

Lower chlorinated compounds such as cis-dichloroethene (cis-DCE) and vinyl chloride (VC) often accumulate in chloroethene-contaminated aquifers due to incomplete reductive dechlorination of higher chlorinated compounds. A highly enriched aerobic culture that degrades VC as a growth substrate was obtained from a chloroethene-contaminated aquifer material. The culture rapidly degraded 50-250 microM aqueous VC to below GC detection limit with a first-order rate constant of 0.2 day(-1). Besides VC, the culture also degraded ethene as the sole carbon source. In addition, the culture degraded cis-DCE, but only in the presence of VC. However, no degradation of trans-DCE or TCE occurred either in the presence or absence of VC. The ability of the TRW culture to degrade cis-DCE is significant for natural attenuation since both VC and cis-DCE are often found in chloroethene-contaminated groundwater. Experiments examining the effect of oxygen threshold on VC degradation showed that the culture was able to metabolize VC efficiently at extremely low concentrations of dissolved oxygen (DO). Complete removal of 150 micromoles of VC occurred in the presence of only 0.2 mmol of oxygen (1.8 mg/L DO). This is important since most groundwater environments contain low DO (1-2 mg/L). Studies showed that the culture was able to withstand long periods of VC starvation. For example, the culture was able to assimilate VC with minimal lag time even after 5 months of starvation. This is impressive from the point of its sustenance under field conditions. Overall the culture is robust and degrades VC to below the detection limit rendering this culture suitable for field application.