Biofilter performance and characterization of a biocatalyst degrading alkylbenzene gases

A biofilter treating alkylbenzene vapors was characterized for its optimal running conditions and kinetic parame-ters. Kinetics of the continuous biofilter were compared to batch kinetic data obtained with biofilm samples as well as with defined microbial consortia and with pure culture isolates from the biofilter. Both bacteria and fungi were present in the bioreactor. Five strains were isolated. Two bacteria, Bacillus and Pseudomonas, were shown to be dominant, as well as a Trichosporon strain which could, however, hardly grow on alkylbenzenes in pure culture. The remaining two strains were most often overgrown by the other three organisms in liquid phase batch cultures μ _max, K_S, K_I values and biodegradation rates were calculated and compared for the difterent mixed and pure cultures. Since filter bed acidification was observed during biofiltration studies reaching a pH of about 4, experiments were also undertaken to study the influence of pH on performance of the different cultures. Biodegradation and growth were possible in all cases, over the pH range 3.5–7.0 at appreciable rates, both with mixed cultures and with pure bacterial cultures. Under certain conditions, microbial activity was even observed in the presence of alkylbenzenes down to pH 2.5 with mixed cultures, which is quite unusual and explains the ability of the present biocatalyst to remove alkylbenzenes with high efficiency in biofilters under acidic conditions.     

Modeling speciation effects on biodegradation in mixed metal/chelate systems

A new model, CCBATCH, comprehensively couples microbially catalyzed reactions to aqueous geochemistry. The effect of aqueous speciation on biodegradation reactions and the effect of biological reactions on the concentration of chemical species (e.g. H₂CO₃, NH ₄ ⁺ , O₂) are explicitly included in CCBATCH, allowing systematic investigation of kinetically controlled biological reactions. Bulk-phase chemical speciation reactions including acid/base and complexation are modeled as thermodynamically controlled, while biological reactions are modeled as kinetically controlled. A dual-Monod kinetic formulation for biological degradation reactions is coupled with stoichiometry for the degradation reaction to predict the rate of change of all biological and chemical species affected by the biological reactions. The capability of CCBATCH to capture pH and speciation effects on biological reactions is demonstrated by a series of modeling examples for the citrate/Fe(III) system. pH controls the concentration of potentially biologically available forms of citrate. When the percentage of the degradable substrate is low due to complexation or acid/base speciation, degradation rates may be slow despite high concentrations of substrate Complexation reactions that sequester substratein non-degradable forms may prevent degradation or stopdegradation reactions prior to complete substrate utilization. The capability of CCBATCH to couple aqueous speciation changes to biodegradation reaction kinetics and stoichiometry allows prediction of these key behaviors in mixed metal/chelate systems.     

Malathion biodegradation by a psychrotolerant bacteria Ochrobactrum sp. M1D and metabolic pathway analysis

An organophosphorus pesticide malathion biodegradation was investigated by using the bacteria Ochrobactrum sp. M1D isolated from a soil sample of peach orchards in Palampur, District Kangra, Himachal Pradesh (India). The bacterium was able to utilize malathion as the sole source of carbon and energy. The isolated bacterium was found psychrotolerant and could degrade 100% of 100 mg l⁻¹ malathion in minimal salt medium at 20°C, pH 7·0 within 12 days with no major significant metabolites left at the end of the study. Through GCMS analysis, methyl phosphate, diethyl maleate, and diethyl 2-mercaptosuccinate were detected and identified as the major pathway metabolites. Based on the GCMS profile, three probable degradation pathways were interpreted. The present study is the first report of malathion biodegradation at both the psychrophilic and mesophilic conditions by any psychrotolerant strain and also through multiple degradation pathways. In the future, the strain can be explored to bio-remediate the malathion contaminated soil in the cold climatic region and to utilize the enzymatic systems for advanced biotechnology applications.     

The Bioutilization of Thiodiglycol (a Detoxication Product of Mustard Gas): Isolation of Degrading Strains and Investigation of Degradation Conditions

The Alcaligenes xylosoxydans subsp.denitrificans strain TD1 capable of degrading thiodiglycol (TDG), a product of mustard gas hydrolysis, was isolated from soil contaminated with breakdown products of this chemical warfare agent. The selected stable variant of TD1 (strain TD2) can grow on TDG with a lag phase of 4–8 h and a specific growth rate of 0.04–0.045 h^–1. Optimal conditions for the biodegradation of TDG (pH, the concentration of TDG in the medium, and specific substrate loading) were determined. TDG was found to be degraded with the formation of diglycolsulfoxide and thiodiglycolic acid as intermediate products. The data obtained can be used to develop approaches to the bioremediation of mustard gas–contaminated soils.     

Effects of organic compounds on the degradation ofp-nitrophenol in lake and industrial wastewater by inoculated bacteria

Many microorganisms fail to degrade pollutants when introduced in different natural environments. This is a problem in selecting inocula for bioremediation of polluted sites. Thus, a study was conducted to determine the success of four inoculants to degradep-nitrophenol (PNP) in lake and industrial wastewater and the effects of organic compounds on the degradation of high and low concentrations of PNP in these environments.Corynebacterium strain Z4 when inoculated into the lake and wastewater samples containing 20 µg/ml of PNP degraded 90% of PNP in one day. Addition of 100 µg/ml of glucose as a second substrate did not enhance the degradation of PNP and the bacterium utilized the two substrates simultaneously. Glucose used at the same concentration (100 µg/ml), inhibited degradation of 20 µg of PNP in wastewater byPseudomonas strain MS. However, glucose increased the extent of degradation of PNP byPseudomonas strain GR. Phenol also enhanced the degradation of PNP in wastewater byPseudomonas strain GR, but had no effect on the degradation of PNP byCorynebacterium strain Z4.Addition of 100 µg/ml of glucose as a second substrate into the lake water samples containing low concentration of PNP (26 ng/ml) enhanced the degradation of PNP and the growth ofCorynebacterium strain Z4. In the presence of glucose, it grew from 2×10⁴ to 4×10⁴ cells/ml in 3 days and degraded 70% of PNP as compared to samples without glucose in which the bacterium declined in cell number from 2×10⁴ to 8×10³ cells/ml and degraded only 30% PNP. The results suggest that in inoculation to enhance biodegradation, depending on the inoculant, second organic substrate many play an important role in controlling the rate and extent of biodegradation of organic compounds.Abbreviations PNP p-nitrophenol     

Selection and isolation of bacteria capable of degrading dinoseb (2-sec-buty-4,6-dinitrophenol)

Dinoseb (2-sec-butyl-4,6-dinitrophenol) has been a widely used herbicide that persists in some contaminated soils, and has been found in groundwaters, causing health and environmental hazards. Persistence in some soils may stem from a lack of dinoseb-degrading organisms. We established a chemostat environment that was strongly selective for aerobic (liquid phase) and anaerobic (sediment phase) bacteria able to degrade dinoseb. The chemostat yielded five taxonomically diverse aerobic isolates that could transform dinoseb to reduced products under microaerophilic or denitrifying conditions, but these organisms were unable to degrade the entire dinoseb molecule, and the transformed products formed multimeric material. The chemostat also yielded an anaerobic consortium of bacteria that could completely degrade dinoseb to acetate and CO₂ when the Eh of the medium was less than-200 mV. The consortium contained at least three morphologically different bacterial species. HPLC analysis indicated that dinoseb was degraded sequentially via several as yet unidentified products. Degradation of these intermediates was inhibited by addition of bromoethane sulfonic acid. GC-MS analysis of metabolites in culture medium suggested that regiospecific attacks occurred non-sequentially on both the nitro groups and the side-chain of dinoseb. The consortium was also able to degrade 4,6-dinitro-o-cresol, 3,5-dinitrobenzoic acid, 2,4-dinitrotoluene, and 2,6-dinitrotoluene via a similar series of intermediate products. The consortium was not able to degrade 2,4-dinitrophenol. To our knowledge, this is the first report of strictly anaerobic biodegradation of an aromatic compound containing a multicarbon, saturated hydrocarbon side chain.Abbreviations BESA bromoethane sulfonic acid - RAMM reduced anaerobic mineral medium     

Isolation of soil Streptomyces strains capable of degrading humic acids and analysis of their peroxidase activity

Abstract Fifteen Streptomyces strains capable of decolorizing humic acids in presence of glucose were isolated from soil samples using the dilute suspension technique and spread on agar plates. Six strains, displaying a significant and stable activity, were selected for further characterization. Some features of these isolates (carbon source utilization, enzyme production, antibiotic resistance) were compared with those of the reference strain Streptomyces viridosporus ATCC 39115. Degradation properties studied in batch cultures at pH 7.0 showed that the catabolic activity on humic acids was generally stimulated by incubation with 100% oxygen and was cell surface-associated. Peroxidase activity from cell-free extracts was analysed by using the oxidation of N,N,N′,N′-tetramethyl-phenylene-diamine. PAGE analysis revealed the existence of two major types of peroxidases (molecular mass: about 39.2 and 61.6 kDa), dividing the strains into two groups. The role of cell surface-associated peroxidase activity in the breakdown of humic acids is discussed.     

Metabolism of halohydroquinones inRhodococcus chlorophenolicus PCP-1

The actinomyceteRhodococcus chlorophenolicus PCP-1 metabolises pentachlorophenol into ultimate inorganic end products via tetrachloro-p-hydroquinone. This intermediate was further dehalogenated in the cytoplasm requiring reductant in the cell free system. Tetrafluoro-p-hydroquinone and tetrabromo-p-hydroquinone were also dehalogenated. Chlorophenol analogs, thiol blocking agents and molecular oxygen inhibited the activity. The dehalogenating reactions led to 1,2,4-trihydroxybenzene, which was further metabolized into maleic acid.Abbreviations PCP pentachlorophenol - TeCH tetrachloro-p-hydroquinone - TeFH tetrafluoro-p-hydroquinone - TeBH tetrabromo-p-hydroquinone - THB trihydroxybenzene     

Applications of Hydrolytic and Decarboxylating Enzymes in Biotransformations

Peptides, and oligosaccharides and glycosides, can be synthesised by making use of the ‘reverse hydrolytic activity’ of proteases and glycosidases respectively. In applying these enzymes to the practical synthesis of these classes of compound, several factors need to be considered, namely the need to shift the rate-determining step through the use of activated substrates, the need to minimise competing hydrolysis of these and the need to minimise hydrolysis of the products. In spite of these problems, the enzymatic methods have many attractive features, not least amongst which is the absolute control of stereochemistry in acyl transfer and glycosyl transfer respectively.