Degradation of pentachlorophenol by polyurethane-immobilized Flavobacterium cells

Comparative insight of pesticide transformations between river and wetland systems

The widespread use of pesticides threatens the environment and ecosystems. Despite the positive effects of plant protection products, pesticides also have unexpected negative effects on nontarget organisms. The microbial biodegradation of pesticides is one of the major pathways for reducing their risks at aquatic ecosystems. The objective of this study was to compare the biodegradability of pesticides in simulated wetland and river systems. Parallel experiments were conducted with 17 pesticides based on the OECD 309 guidelines. A comprehensive analytical method, such as target screening combined with suspect and non-target screening, was performed to evaluate the biodegradation via identification of transformation products (TPs) using LC-HRMS. As evidence of biodegradation, we identified 97 TPs for 15 pesticides. Metolachlor and dimethenamid had 23 and 16 TPs, respectively, including Phase II glutathione conjugates. The analysis of 16S rRNA sequences for microbials characterized operational taxonomic units. Rheinheimera and Flavobacterium, which have the potential for glutathione S-transferase, were dominant in wetland systems. Estimation of toxicity, biodegradability, and hydrophobicity using QSAR prediction indicated lower environmental risks of detected TPs. We conclude that the wetland system is more favorable for pesticide degradation and risk mitigation mainly attributed to the abundance and variety of the microbial communities.

Monitoring of the effects of a temporally limited heat stress on microbial communities in a shallow aquifer

Aquifer thermal energy storage (ATES) is a key concept for the use of renewable energy resources. Interest in ATES performed at high temperature (HT-ATES; > 60 °C) is increasing due to higher energetic efficiencies. HT-ATES induces temperature fluctuations that exceed the natural variability in shallow aquifers, which could lead to adverse effects in subsurface ecosystems by altering the groundwater chemistry, biodiversity, and microbial metabolic activity, resulting in changes of the groundwater quality, biogeochemical processes, and ecosystem functions. The aim of this study was to emulate the initial operating phase of a HT-ATES system with a short-term infiltration of warm water into Pleistocene sandur sediment and, consequently, to monitor the thermal effects on the groundwater microbiome inhabiting an imitated affected space of an HT-ATES system. Therefore, local groundwater was withdrawn, heated up to 75 °C, and re-infiltrated into a shallow aquifer located near Wittstock/Dosse (Brandenburg, Germany) for around five days. Groundwater samples taken regularly before and after the infiltration were analyzed by 16S rRNA gene amplicon sequencing for microbial diversity analyses as well as total cell counting. During the infiltration, a thermal plume with groundwater temperatures increasing from 9 ± 2 to up to ~65 °C was recorded. The highest temperature at which groundwater samples were taken was 34.9 °C, a temperature typically arising in the affected space of an HT-ATES system. The microbial communities in the groundwater were mainly composed of Gammaproteobacteria, Alphaproteobacteria, Bacteroidia, and Actinobacteria, and the total cell numbers ranged from 3.2 * 10⁴ to 3.1 * 10⁶ cells ml^-1. Neither the compositions of the microbial communities nor the total number of cells in groundwater were significantly changed upon moderate temperature increase, indicating that the diverse groundwater microbiome was resilient to the temporally limited heat stress.

Identification and characterization of cresol degrading Pseudomonas monteilii strain SHY from Soil samples

Cresol is an organic pollutant discharged by pharmaceutical, pesticide, coal and gasification industries causing severe organ failure in humans. Therefore, it is of interest to isolate microbes from contaminated site for degrading cresol. We isolated a strain (CR-13) that survives at 5000ppm cresol with about 80 percent cresol degradation ability. Immobilized cells showed >99 percent degradation at high concentration of cresol. The 16S rRNA sequence (accession number: MF278026) deposited in GenBank was used for phylogenetic tree analysis and the strain was grouped under Pseudomonas monteilii. The isolated cresol degrading strain was subsequently named as Pseudomonas monteilii SHY.

Enhancing methyl parathion degradation by the immobilization of Burkholderia sp. isolated from agricultural soils

Organophosphate pesticides are of great interest for research because they are currently the most commonly used pesticides. In this study, a bacterial strain capable of completely degrading methyl parathion (MP) was isolated from agricultural soils in central Mexico. This strain was designated strain S5-2 and was identified as Burkholderia cenocepacia. To increase degradation yields, cells were immobilized on three different supports: powdered zeolite and Opuntia sp. and Agave sp. fibers. The results indicated a significant increase in MP hydrolysis and p-nitrophenol (PNP) degradation with immobilized cells compared to free cell cultures. Furthermore, immobilized cells were capable of withstanding and degrading higher concentrations of PNP compared to cell suspension cultures. The cell viability in the free cell cultures, as well as PNP degradation, was affected at concentrations greater than 25 mg/L. In contrast, cells immobilized on Opuntia sp. and Agave sp. fibers completely degraded PNP at concentrations of 100 mg/L. To verify that MP solution toxicity was decreased by B. cenocepacia strain S5-2 via pesticide degradation, we measured the acetylcholinesterase activity, both before and after treatment with bacteria. The results demonstrate that the activity of acetylcholinesterase was unaffected after MP degradation by bacteria.

Distinct Network Interactions in Particle-Associated and Free-Living Bacterial Communities during a Microcystis aeruginosa Bloom in a Plateau Lake

Particle-associated bacteria (PAB) and free-living bacteria (FLB) from aquatic environments during phytoplankton blooms differ in their physical distance from algae. Both the interactions within PAB and FLB community fractions and their relationship with the surrounding environmental properties are largely unknown. Here, by using high-throughput sequencing and network-based analyses, we compared the community and network characteristics of PAB and FLB from a plateau lake during a Microcystis aeruginosa bloom. Results showed that PAB and FLB differed significantly in diversity, structure and microbial connecting network. PAB communities were characterized by highly similar bacterial community structure in different sites, tighter network connections, important topological roles for the bloom-causing M. aeruginosa and Alphaproteobacteria, especially for the potentially nitrogen-fixing (Pleomorphomonas) and algicidal bacteria (Brevundimonas sp.). FLB communities were sensitive to the detected environmental factors and were characterized by significantly higher bacterial diversity, less connectivity, larger network size and marginal role of M. aeruginosa. In both networks, covariation among bacterial taxa was extensive (>88% positive connections), and bacteria potentially affiliated with biogeochemical cycling of nitrogen (i.e., denitrification, nitrogen-fixation and nitrite-oxidization) were important in occupying module hubs, such as Meganema, Pleomorphomonas, and Nitrospira. These findings highlight the importance of considering microbial network interactions for the understanding of blooms.

Immobilization of Microbes for Bioremediation of Crude Oil Polluted Environments: A Mini Review

Petroleum hydrocarbons are the most common environmental pollutants in the world and oil spills pose a great hazard to terrestrial and marine ecosystems. Oil pollution may arise either accidentally or operationally whenever oil is produced, transported, stored and processed or used at sea or on land. Oil spills are a major menace to the environment as they severely damage the surrounding ecosystems. To improve the survival and retention of the bioremediation agents in the contaminated sites, bacterial cells must be immobilized. Immobilized cells are widely tested for a variety of applications. There are many types of support and immobilization techniques that can be selected based on the sort of application. In this review article, we have discussed the potential of immobilized microbial cells to degrade petroleum hydrocarbons. In some studies, enhanced degradation with immobilized cells as compared to free living bacterial cells for the treatment of oil contaminated areas have been shown. It was demonstrated that immobilized cell to be effective and is better, faster, and can be occurred for a longer period.

Application of the adhesive bacterionanofiber AtaA to a novel microbial immobilization method for the production of indigo as a model chemical

The toluene-degrading bacterium Acinetobacter sp. Tol 5 shows high adhesiveness mediated by the bacterionanofiber protein AtaA, which is a new member of the trimeric autotransporter adhesin (TAA) family. In contrast to other reported TAAs, AtaA mediates the adhesion of Tol 5 to various abiotic surfaces ranging from hydrophobic plastics to hydrophilic glass and stainless steel. The expression of ataA in industrially relevant bacteria improves their adhesiveness and enables immobilization directly onto support materials. This represents a new method that can be alternated with conventional immobilization via gel entrapment and chemical bonding. In this study, we demonstrate the feasibility of this immobilizing method by utilizing AtaA. As a model case for this method, the indigo producer Acinetobacter sp. ST-550 was transformed with ataA and immobilized on a polyurethane support. The immobilized ST-550 cells were transferred directly to a reaction solution containing indole as the substrate. The immobilized ST-550 cells showed a faster indigo production rate at high concentrations of indole compared with planktonic ST-550 not expressing the ataA gene, implying that immobilization enhanced the tolerance of ST-550 to the substrate indole. As a result, the immobilized ST-550 produced fivefold higher levels of indigo than planktonic ST-550. These results proved that AtaA is useful for bacterial immobilization.

Enhancement of the diesel oil degradation ability of a marine bacterial strain by immobilization on a novel compound carrier material

A novel floatable and biodegradable carrier material was made by coating puffed foxtail millet (PFM) with a calcium alginate (CA)-chitosan compound membrane. A diesel oil-degrading marine bacterial strain, Acinetobacter sp. F9, was immobilized on the carrier material. The number of viable F9 cells immobilized on the carrier material reached approximately 5×10(9) CFU/g. This formulation could be stored at -20°C and 4°C for 10 weeks without a significant decrease in the number of viable immobilized cells. SEM results showed that the coating membrane was porous and that F9 cells were immobilized on the walls of the pores. The immobilized F9 cells were able to remove more than 90% of the diesel oil by the second day, while free F9 cells did not remove 90% of the diesel oil until the seventh day. GC-MS analysis indicated that the immobilized F9 cells could remove diesel oil more completely than free cells. The immobilization of the F9 cells enhanced their ability to biodegrade diesel oil.

Pentachlorophenol sorption in nylon fiber and removal by immobilized Rhizopus oryzae ENHE

This study describes pentachlophenol (PCP) sorption in nylon fiber in which Rhizopus oryzae ENHE was immobilized to remove the chemical compound. The experimental sorption data were analyzed using the Langmuir, Freundlich, and Redlich-Peterson isotherm models using non-linear error functions to fit the experimental data to the three models. Results showed that the isotherm obtained from the data fitted the three models used. However, the g parameter from Redlich-Peterson model showed that the isotherm obtained approaches the Freundlich model. This support reached the sorption equilibrium concentration at 3mg PCPg(-1)nylon. To study PCP removal capability by R. oryzae ENHE and to eliminate the error caused by PCP sorbed by the nylon fiber during its quantification, nylon fiber at PCP equilibrium sorption concentration was used to immobilize R. oryzae ENHE. It was found that this fungus grew within nylon fiber cubes in presence or not of PCP, even when PCP caused growth inhibition. Maximum biomass accumulated into nylon cubes without PCP was of 32 mg biomass g(-1)nylon and into nylon cubes at PCP equilibrium concentration was of 18 mg g(-1)nylon. The results showed that R. oryzae ENHE immobilized into nylon fiber removed 88.6% and 92% of PCP in cultures with 12.5 and 25 mg PCPL(-1), as initial concentration, respectively. This is the first work to report that a zygomycete, such as R. oryzae ENHE, immobilized into nylon fiber kept its potential to remove PCP.

Degradation of h-acid by free and immobilized cells of Alcaligenes latus

Alcaligenes latus, isolated from industrial effluent, was able to grow in mineral salts medium with 50 ppm (0.15 mM) of H-acid as a sole source of carbon. Immobilization of Alcaligenes latus in Ca-alginate and polyurethane foam resulted in cells embedded in the matrices. When free cells and immobilized cells were used for biodegradation studies at concentration ranging from 100 ppm (0.3 mM) to 500 ppm (1.15 mM) degradation rate was enhanced with immobilized cells. Cells immobilized in polyurethane foam showed 100% degradation up to 350 ppm (1.05 mM) and 57% degradation at 500 ppm (1.5 mM). Degradation rate of Ca-alginate immobilized cells was less as compared to that of polyurethane foam immobilized cells. With Ca-alginate immobilized cells 100% degradation was recorded up to 200 ppm (0.6 mM) of H-acid and only 33% degradation was recorded at 500 ppm (1.5 mM) of H-acid. Spectral analysis of the products after H-acid utilization showed that the spent medium did not contain any aromatic compounds indicating H-acid degradation by A. latus.

Immobilized viable microbial cells: from the process to the proteome… or the cart before the horse

Biotechnological processes based on immobilized viable cells have developed rapidly over the last 30 years. For a long time, basic studies of the physiological behaviour of immobilized cells (IC) have remained in the shadow of the applications. Natural IC structures, i.e. biofilms, are being increasingly investigated at the cellular level owing to their definite importance for human health and in various areas of industrial and environmental relevance. This review illustrates this paradoxical development of research on ICs, starting from the initial rationale for IC emergence and main application fields of the technology--with particular emphasis on those that exploit the extraordinary resistance of ICs to antimicrobial compounds--to recent advances in the proteomic approach of IC physiology.

Degradation of carbendazim and 2,4-dichlorophenoxyacetic acid by immobilized consortium on loofa sponge

A fungicide, carbendazim (methyl-2-benzimidazole carbamate; MBC), and a herbicide, 2,4-dichlorophenoxyacetic acid (2,4-D), could be simultaneously degraded by a microbial consortium obtained from several soil samples in Japanese paddy fields with enrichment continuous culture. The degradation ability of the consortium was increased by immobilization on loofa (Luffa cylindrica) sponge in comparison with that of free-living consortium. MBC and 2,4-D were completely degraded within 5.5 d and 1.5 d, respectively. The toxicity of these pesticides in culture medium to Daphnia magna was reduced by treatment with the consortium corresponding to their degradation. The degradation ability of the immobilized consortium at pHs in the range from 6 to 9, at temperatures from 15 degrees C to 37 degrees C, and at low NH(4)(+)-N concentrations (1-10 mg/l) was not very different from that under the basal condition (pH 7, 30 degrees C, 424 mg/l NH(4)(+)-N and 472 mg/l PO(4)(3)(-)-P). At low pHs 4 and 5, the ability was significantly lower than that of the basal condition. Moreover, incubation at low PO(4)(3)(-)-P concentrations (1-10 mg/l) caused a decrease in pH at which the degradation ability also became lower. However, the ability in this culture completely recovered when pH was adjusted to 7 or the phosphate concentration was increased to the basal level. Analysis by denaturing gradient gel electrophoresis (DGGE) showed the whole population of the consortium became faint at low pH or low phosphate concentrations but became distinct again as much as those under the basal conditions, indicating that the decrease in the degradation ability caused by low pH was due to that whole population of the consortium underwent serious damage but could survive and recover. These results suggest the immobilized consortium on loofa sponge is a promising material for bioremediation of polluted water with these pesticides in paddy fields.

Disposal and degradation of pesticide waste

Generation of pesticide waste is inevitable during every agricultural operation from storage to use and equipment cleanup. Large-scale pesticide manufacturers can afford sophisticated recovery, treatment, and cleanup techniques. Small-scale pesticide users, for example, single farms or small application businesses, struggle with both past waste problems, including contaminated soils, and disposal of unused product and equipment rinsewater. Many of these problems have arisen as a result of inability to properly handle spills during, equipment loading and rinsewater generated after application. Small-scale facilities also face continued problems of wastewater handling. Old, obsolete pesticide stocks are a vexing problem in numerous developing countries. Pesticide waste is characterized by high concentrations of a diversity of chemicals and associated adjuvants. Dissipation of chemicals at elevated concentrations is much slower than at lower concentrations, in part because of microbial toxicity and mass transfer limitations. High concentrations of pesticides may also move faster to lower soil depths, especially when pore water becomes saturated wish a compound. Thus, if pesticide waste is not properly disposed of, groundwater and surface water contamination become probable. The Waste Management Hierarchy developed as an Australian Code of Practice can serve as a guide for development of a sound waste management plan. In order of desirability, the course of actions include waste avoidance, waste reduction, waste recycling, waste treatment, and waste disposal. Proper management of pesticide stocks, including adequate storage conditions, good inventory practices, and regular turnover of products,. will contribute to waste avoidance and reduction over the long-term. Farmers can also choose to use registered materials that have the lowest recommended application rates or are applied in the least volume of water. Wastewater that is generated during equipment rinsing can be recycled by spraying it onto cropland, thus avoiding a soil contamination problem. If it is not feasible to spray out rinsates, then water treatment becomes necessary. However, for small waste generators, practical technology is still too experimental and not easily implemented on an individual farm or at a small application business. Nevertheless, research has been quite active in application of advanced oxidation processes (UV/ozonation: photoassisted Fenton reaction: photocatalysis using TiO2). Obsolete pesticide stocks in developing countries are being packaged and shipped to developed countries for incineration. Contaminated soil can also be incinerated, but this is not practical nor affordable for small waste generators. Chemical degradation of chlorinated hydrocarbon pesticides may be amenable to dechlorination by alkali polyethylene glycol treatment, but further study is needed to make the technique practical for small waste generators. Contaminated soils may be amenable to cleanup by one of several biological treatment methods, including composting, landfarming, and bioaugmentation/ biostimulation. Composting and landfarming (which may be used in combination with biostimulation) may be the most practical of the biological methods that is immediately ready for implementation by small-scale pesticide waste generators.

Biodegradation of crude oil across a wide range of salinities by an extremely halotolerant bacterial consortium MPD-M, immobilized onto polypropylene fibers

The bacterial consortium MPD-M, isolated from sediment associated with Colombian mangrove roots, was effective in the treatment of hydrocarbons in water with salinities varying from 0 to 180 g L(-1). Where the salinity of the culture medium surpassed 20 g L(-1), its effectiveness increased when the cells were immobilized on polypropylene fibers. Over the range of salinity evaluated, the immobilized cells significantly enhanced the biodegradation rate of crude oil compared with free-living cells, especially with increasing salinity in the culture medium. Contrary to that observed in free cell systems, the bacterial consortium MPD-M was highly stable in immobilized systems and it was not greatly affected by increments in salinity. Biodegradation was evident even at the highest salinity evaluated (180 g L(-1)), where biodegradation was between 4 and 7 times higher with immobilized cells compared to free cells. The biodegradation of pristane (PR) and phytane (PH) and of the aromatic fraction was also increased using cells immobilized on polypropylene fibers.

Calcite precipitation induced by polyurethane-immobilized Bacillus pasteurii

Polyurethane (PU) foam was used to immobilize the whole cell of Bacillus pasteurii. The immobilized cells exhibited the rates of calcite precipitation and ammonia production as high as those of the free cells. Scanning electron micrographs identified the cells embedded in calcite crystals throughout PU matrices. Calcite in PU showed little effect on the elastic modulus and tensile strength of the polymer, but increased the compressive strengths of concrete cubes, whose cracks were remediated with PU-immobilized cells. These observations led us to believe that the calcite might remain as a form of precipitation, not as a bonding material within the matrices.

Microbial degradation of 4-chlorophenol by microorganisms entrapped in carrageenan-chitosan gels

A new cell immobilization method based on the replacement of KCl by KCl + chitosan as gelling agent was developed. The results showed that through addition of chitosan into gelling agent, the mechanical strength and thermal stability of the carrageenan gel were greatly improved. The new immobilization method was used to entrap a chlorophenol-degrading microorganism. The immobilized microbial cells were applied for chlorophenol biodegradation. The experiments demonstrated that immobilized cells exhibit a higher bioactivity in the degradation of chlorophenol than free cells.

The use of live biocatalysts for pesticide detoxification

During the past decade, numerous microorganisms capable of degrading pesticides have been isolated, and detoxification processes based on these live biocatalysts have been developed. Recently, novel detoxification strategies using genetically engineered microorganisms with extended degradative capabilities have been investigated and, in some cases, shown to be more effective. One promising approach for the detoxification of organophosphate pesticides uses genetically engineered Escherichia coli with surface-expressed organophosphorus hydrolase. Continuous efforts in this direction are required, in conjunction with a search for microorganisms capable of degrading pesticides rapidly, to establish efficient and cost-effective large-scale processes for pesticide detoxification.

Aerobic dechlorination of low-chlorinated biphenyls by bacterial biofilms in packed-bed batch bioreactors

Cells of an aerobic three-membered bacterial co-culture, designated as ECO3, capable of cometabolizing and aerobically dechlorinating low-chlorinated biphenyls in the presence of biphenyl, were immobilized on Manville silica beads, on frosted-glass beads and on polyurethane foam cubes in packed-bed bioreactors continuously fed with a biphenyl-saturated air stream. The ECO3 biofilm reactors were found to be capable of extensively mineralizing several pure dichlorobiphenyls (75 mg/l) and Aroclor 1221 (75 mg/l) in batch mode. Immobilized ECO3 cells could aerobically degrade and dechlorinate the dichlorobiphenyls tested more extensively than suspended ECO3 cells. Among the three biofilm reactors, the glass bead bioreactor and the polyurethane bioreactor exhibited the highest capability of mineralizing both dichlorobiphenyls and Aroclor 1221; the polychlorinated biphenyl availability in the bioreactors more than the biomass availability, both depending on the nature of the support employed, significantly governed the efficiency of the treatment. These results are of interest for the possible development of a bioreactor system for continuous treatment of polychlorinated-biphenyl-contaminated wastewaters.

Influence of a supplementary carbon source on biodegradation of pyridine by freely suspended and immobilized Pimelobacter sp

The effect of the presence of supplementary glucose or acetate on the growth and pyridine-degrading activity of freely suspended and calcium-alginate-immobilized Pimelobacter sp. was investigated. Although the supplementary carbon sources could be degraded simultaneously with pyridine, Pimelobacter sp. exhibited a preference for pyridine over supplementary carbon sources. Thus, the pyridine-degrading activity of the freely suspended cells was not decreased significantly by the addition of either glucose (1.5-6 mM) or acetate (6-24 mM) to the pyridine (6-24 mM). In the semi-continuous immobilized cell culture, immobilized cells also exhibited a preference for pyridine over supplementary carbon sources and did not switch their substrate preference throughout the culture. Owing to a high cell concentration, the volumetric pyridine degradation rate at 24 mM pyridine in the immobilized cell culture was approximately six times higher than that in the freely suspended cell culture. Furthermore, the immobilized cells could be reused 16 times without losing their pyridine-degrading activity during the culture period tested. Taken together, the use of immobilized Pimelobacter sp. for the degradation of pyridine is quite feasible because of the preference for pyridine over supplementary carbon sources, the high volumetric pyridine degradation rate, and the reusability of immobilized cells.

Hydrophobic adsorption of aromatic compounds on polyurethane foam as a carbon source for Pseudomonas growth

The use of polyurethane foam appears to be efficient to extract hydrophobic pollutants from aqueous media. Their adsorption is the result of spontaneous hydrophobic interactions with the foam, The rate of adsorption is a function of the diffusion of the molecules into the foam as well as their hydrophilic/lipophilic balance. A mixture of different molecules modifies the adsorption capacities of each type of molecule on the foam, probably resulting from stacking phenomena between the molecules. The Pseudomonas species can grow in the presence of the polyurethane foam and be adsorbed on it. Moreover, a strain of Pseudomonas pseudoalcaligenes tested in this study can use adsorbed biphenyl as the sole carbon source. Polyurethane foam therefore shows favorable characteristics for being chosen as a method of concentrating aromatic compounds and optimizing the rate of degradation of these molecules by bacteria.

Biodegradation of chlorophenols by mixed and pure cultures from a fluidized-bed reactor

An aerobic, continuous-flow fluidized-bed reactor was established with inoculum from activated sludge, and fed a mixture of 2,4,6-trichlorophenol (TCP), 2,3,4,6-tetrachlorophenol (TeCP) and pentachlorophenol (PCP) as the sole sources of carbon and energy for 2 years. Experiments with the enrichment were performed with material from the reactor. Later, degradation experiments were completed using pure cultures of bacteria that were isolated from suspended samples of the carrier biofilm. In batch-bottle bioassays, the reactor enrichment degraded PCP, TeCP and TCP both in mineral salts (MS) and tryptone-yeast extract-glucose (TGY) media. ortho-Methoxylated chlorophenols including 4,5-dichloroguaiacol (4,5-DCG), tetrachloroguaiacol (TeCG) and trichlorosyringol (TCS) resisted biodegradation by the enrichment both in MS and TGY media, whereas 5,6-dichlorovanillin (5,6-DCV) was readily transformed to an unidentified metabolite. Experiments with 14C labeled chlorophenols showed mineralization of 2,4-dichlorophenol (DCP) and 2,3,5-TCP to 14CO2 by the enrichment. Material from the suspended biofilm after continuous chlorophenol feeding for 2 years was inoculated onto TGY-agar plates, and showed predominantly two colony types accounting for over 99% of the total colony counts. The two colony types, were equal in abundance. Six Gram-negative, oxidase- and catalase-positive, nonfermentative small rods were isolated in TGY agar media supplemented with 10 mg/l of TeCP or PCP. All isolates formed colonies in TGY plus 150 mg/l of PCP. The isolates degraded TCP and TeCP but not PCP. In mixtures of isolated bacteria the rates of chlorophenol degradation were similar to those observed with individual isolates. Three isolates were identified as Pseudomonas saccharophila and three were an unidentified species of Pseudomonas.

Bacterial dehalogenases: biochemistry, genetics, and biotechnological applications

This review is a survey of bacterial dehalogenases that catalyze the cleavage of halogen substituents from haloaromatics, haloalkanes, haloalcohols, and haloalkanoic acids. Concerning the enzymatic cleavage of the carbon-halogen bond, seven mechanisms of dehalogenation are known, namely, reductive, oxygenolytic, hydrolytic, and thiolytic dehalogenation; intramolecular nucleophilic displacement; dehydrohalogenation; and hydration. Spontaneous dehalogenation reactions may occur as a result of chemical decomposition of unstable primary products of an unassociated enzyme reaction, and fortuitous dehalogenation can result from the action of broad-specificity enzymes converting halogenated analogs of their natural substrate. Reductive dehalogenation either is catalyzed by a specific dehalogenase or may be mediated by free or enzyme-bound transition metal cofactors (porphyrins, corrins). Desulfomonile tiedjei DCB-1 couples energy conservation to a reductive dechlorination reaction. The biochemistry and genetics of oxygenolytic and hydrolytic haloaromatic dehalogenases are discussed. Concerning the haloalkanes, oxygenases, glutathione S-transferases, halidohydrolases, and dehydrohalogenases are involved in the dehalogenation of different haloalkane compounds. The epoxide-forming halohydrin hydrogen halide lyases form a distinct class of dehalogenases. The dehalogenation of alpha-halosubstituted alkanoic acids is catalyzed by halidohydrolases, which, according to their substrate and inhibitor specificity and mode of product formation, are placed into distinct mechanistic groups. beta-Halosubstituted alkanoic acids are dehalogenated by halidohydrolases acting on the coenzyme A ester of the beta-haloalkanoic acid. Microbial systems offer a versatile potential for biotechnological applications. Because of their enantiomer selectivity, some dehalogenases are used as industrial biocatalysts for the synthesis of chiral compounds. The application of dehalogenases or bacterial strains in environmental protection technologies is discussed in detail.

Characterization of Inorganic Biocarriers That Moderate System Upsets during Fixed-Film Biotreatment Processes

Inorganic matrices were developed for fixed-film bioreactors affording protection to microorganisms and preventing loss of bioreactor productivity during system upsets. These biocarriers, designated Type-Z, contain ion-exchange properties and possess high porosity and a high level of surface area, which provide a suitable medium for microbial colonization. Viable cell populations of 10 9 /g were attainable, and scanning electron micrographs revealed extensive external colonization and moderate internal colonization with aerobic microorganisms. Laboratory-scale bioreactors were established with various biocarriers and colonized with Pseudomonas aeruginosa , and comparative studies were performed. The data indicated that bioreactors containing the Type-Z biocarriers were more proficient at removing phenol (1,000 ppm) than bioreactors established with Flexirings (plastic) and Celite R635 (diatomaceous earth) biocarriers. More significantly, these biocarriers were shown to moderate system upsets that affect operation of full-scale biotreatment processes. For example, subjecting the Type-Z bioreactor to an influent phenol feed at pH 2 for periods of 24 h did not decrease the effluent pH or reactor performance. In contrast, bioreactors containing either Celite or Flexirings demonstrated an effluent pH drop to ∼2.5 and a reduction in reactor performance by 75 to 82%. The Celite reactor recovered after 5 days, whereas the bioreactors containing Flexirings did not recover. Similar advantages were noted during either nutrient or oxygen deprivation experiments as well as alkali and organic system shocks. The available data suggest that Type-Z biocarriers represent an immobilization medium that provides an amenable environment for microbial growth and has the potential for improving the reliability of fixed-film biotreatment processes.

Biodegradation of hexachlorocyclohexane isomers in soil and food environment

Persistence of chlorinated hydrocarbon insecticides in the environment is well documented. One early introduced insecticide, hexachlorocyclohexane (HCH), popularly called BHC, was used in large quantities all over the world until recently. In India, even today, technical grade HCH is being used extensively. Theoretically, HCH has eight possible stereoisomers of which four (alpha, beta, gamma, and delta) predominate in the technical product. These isomers significantly differ between themselves with respect to their persistence and toxicity toward insects, birds, mammals, and other nontarget organisms. The relative proportion of HCH isomers is, therefore, crucial from a toxicology standpoint. This problem assumes importance in light of reports that the HCH isomers undergo interconversion in soil, water, animals, plants, insects, etc. The persistence of HCH can be attributed in part to the interconversion of HCH isomers, which also restrict their solubility. In the present review, biotransformation of HCH isomers, both under aerobic and anaerobic conditions, and their degradation pathways have been described. In addition, emphasis is given to the interconversion of HCH isomers, including interconversion mechanisms, as this area has not received adequate coverage in earlier reviews on HCH.

Hydroxylation and biodegradation of 6-methylquinoline by pseudomonads in aqueous and nonaqueous immobilized-cell bioreactors

Selective culturing of pseudomonads that could degrade quinoline led to enrichment cultures and pure cultures with expanded substrate utilization and transformation capabilities for substituted quinolines in immobilized and batch cultures. Immobilized cells of the pseudomonad cultures rapidly transformed quinolines to hydroxyquinolines in bioreactors and were able to tolerate higher substrate concentrations compared with batch cultures. After prolonged incubation on a mixture of quinoline and 6-methylquinoline, a quinoline-degrading culture of Pseudomonas putida developed the ability to biodegrade 6-methylquinoline, which initially was resistant to microbial attack, as a sole source of carbon and energy. 6-Methylquinoline was also degraded in a nonaqueous solution by this strain of P. putida when a solution of 6-methylquinoline in decane was flowed through an immobilized-cell fixed-bed bioreactor.

Characterization of immobilized enzymes in polyurethane foams in a dynamic bed reactor

beta-D-Galactosidase (E 3.2.1.23) from Aspergillus oryzae was immobilized with polyurethane foam (PUF). Among several immobilization methods attempted in this work, the immobilized enzyme preparation by in-situ co-polymerization between enzyme and prepolymer HYPOL 3000 showed the highest activity. The intrinsic kinetics of PUF-immobilized enzyme was determined in a dynamic bed reactor, used to increase transport rates. The immobilization mechanism in PUF was studied by measurements of immobilized enzyme kinetics and by using scanning electron microscopy combined with immuno-gold labeling techniques. The results showed that immobilization was predominantly by covalent bonding between primary amino groups of beta-D-galactosidase and isocyanate groups of the prepolymers. Entrapment in the PUF micropores assisted the immobilization of enzymes, and adsorption on the surface of macropores was not important for immobilization. The bicinchoninic acid method was applied for the determination of PUF loading capacity and specific enzyme activity and used to determine enzyme deactivation during immobilization.

Microbial breakdown of halogenated aromatic pesticides and related compounds

Considerable progress has been made in the last few years in understanding the mechanisms of microbial degradation of halogenated aromatic compounds. Much is already known about the degradation mechanisms under aerobic conditions, and metabolism under anaerobiosis has lately received increasing attention. The removal of the halogen substituent is a key step in degradation of halogenated aromatics. This may occur as an initial step via reductive, hydrolytic or oxygenolytic mechanisms, or after cleavage of the aromatic ring at a later stage of metabolism. In addition to degradation, several biotransformation reactions, such as methylation and polymerization, may take place and produce more toxic or recalcitrant metabolites. Studies with pure bacterial and fungal cultures have given detailed information on the biodegradation pathways of several halogenated aromatic compounds. Several of the key enzymes have been purified or studied in cell extracts, and there is an increasing understanding of the organization and regulation of the genes involved in haloaromatic degradation. This review will focus on the biodegradation and biotransformation pathways that have been established for halogenated phenols, phenoxyalkanoic acids, benzoic acids, benzenes, anilines and structurally related halogenated aromatic pesticides. There is a growing interest in developing microbiological methods for clean-up of soil and water contaminated with halogenated aromatic compounds.