Search

BACKGROUND 1,1,2,2-Tetrachloroethane (TeCA) has been generally considered as non-biodegradable under aerobic conditions, while its complete biodegradation was reported with microbial consortia growing anaerobically. This study describes TeCA aerobic cometabolic degradation by the propanotroph Rhodococcus aetherivorans strain TPA isolated from a TeCA-degrading consortium. RESULTS R. aetherivorans TPA was able to grow on aliphatic hydrocarbons from propane to pentane and on gaseous n-alkanes metabolic intermediates. The Michaelis–Menten model allowed a satisfactory fit of the TPA propane utilization rates under resting cell conditions, while the TeCA degradation rates were successfully interpolated with Andrew's inhibition model. A significant propane - TeCA mutual inhibition was observed, although the results did not allow to distinguish between competitive and non-competitive inhibition. Among different bioreactor options for the on-site bioremediation of TeCA-contaminated groundwater, a single suspended-cell continuous stirred-tank reactor (CSTR) appeared to be the optimal one. CONCLUSIONS This study provides for the first time the kinetic and microbiological characterization of a bacterial strain capable to degrade TeCA under aerobic conditions.

Microbial degradation of 1,1,2,2-tetrachloroethane has been rarely analysed under aerobic conditions. In this work, the catabolic potential of a TeCA-degrading aerobic propanotroph consortium (C2) and the optimal bioreactor configuration for an on-site TeCA-bioremediation strategy with C2 were defined. More specifically, the diversity of alkane-oxidizing bacteria in C2 was assessed by means of clone libraries of genes coding for alkane monooxygenases (MOs) of different families (AlkB-like alkane hydroxylase, soluble di-iron MO and cytochromes P450). A large number of alkane MO sequences retrieved in this study showed the highest similarity with reference sequences belonging to Rhodococcus genus, suggesting a key role of this genus in TeCA/propane co-metabolism, while the remaining alkane MO sequences were mainly attributed to other Actinobacteria, to Bradhyrizobiaceae, and Cupriavidus genus. Further, the feasibility of an on-site TeCA bioremediation strategy with C2 was evaluated by simulating a continuous-flow aerobic co-metabolic process with different bioreactor configurations. Our results show that the configuration with a suspended-cell continuous stirred-tank reactor (CSTR) followed by a suspended-cell plug-flow reactor (PFR) was the one giving the best performance with consortium C2.

Alkanes are widely distributed in the environment as they not only constitute the large fraction of crude oil but are also produced by many living organisms. They are saturated hydrocarbons of different sizes and structures, which pose a variety of challenges to degradative microorganisms due to their physicochemical properties, i.e., the extremely limited solubility and the high energy required for activation. The hydrophobic cell surface of Rhodococcus spp., the ability to produce biosurfactants, and the possession of a wide range of oxygenases allow coping with such challenges. In particular, monooxygenase enzymes are involved in the activation of alkanes by converting them into alcohols, which undergo a series of oxidation steps before being converted to fatty acids. Rhodococcus alkane monooxygenases belong to different families (i.e., AlkB-like monooxygenase, soluble di-iron monooxygenase, cytochrome P450), have different genetic organization, and are subject to different regulatory mechanisms, which are poorly known. Because of their long-term survival capacity, broad catabolic abilities, and effective contact mechanisms with hydrocarbon molecules, alkanotrophic Rhodococcus strains have biotechnology applications and potential in bioremediation and biotransformation reactions.

Naphthenic acids (NAs) are an important group of toxic organic compounds naturally occurring in hydrocarbon deposits. This work shows that Rhodococcus aetherivorans BCP1 cells not only utilize a mixture of eight different NAs (8XNAs) for growth but they are also capable of marked degradation of two model NAs, cyclohexanecarboxylic acid (CHCA) and cyclopentanecarboxylic acid (CPCA) when supplied at concentrations from 50 to 500 mgL−1 . The growth curves of BCP1 on 8XNAs, CHCA, and CPCA showed an initial lag phase not present in growth on glucose, which presumably was related to the toxic effects of NAs on the cell membrane permeability. BCP1 cell adaptation responses that allowed survival on NAs included changes in cell morphology, production of intracellular bodies and changes in fatty acid composition. Transmission electron microscopy (TEM) analysis of BCP1 cells grown on CHCA or CPCA showed a slight reduction in the cell size, the production of EPS-like material and intracellular electrontransparent and electron-dense inclusion bodies. The electron-transparent inclusions increased in the amount and size in NA-grown BCP1 cells under nitrogen limiting conditions and contained storage lipids as suggested by cell staining with the lipophilic Nile Blue A dye. Lipidomic analyses revealed significant changes with increases of methyl-branched (MBFA) and polyunsaturated fatty acids (PUFA) examining the fatty acid composition of NAs-growing BCP1 cells. PUFA biosynthesis is not usual in bacteria and, together with MBFA, can influence structural and functional processes with resulting effects on cell vitality. Finally, through the use of RT (Reverse Transcription)- qPCR, a gene cluster (chcpca) was found to be transcriptionally induced during the growth on CHCA and CPCA. Based on the expression and bioinformatics results, the predicted products of the chcpca gene cluster are proposed to be involved in aerobic NA degradation in R. aetherivorans BCP1. This study provides first insights into the genetic and metabolic mechanisms allowing a Rhodococcus strain to aerobically degrade NAs.&nbsp

In this work the aerobic cometabolic biodegradation of 1,1,2,2-tetrachloroethane (TeCA) by propane-utilizing bacteria was studied in slurry bioreactors containing soil and groundwater from 5 aquifers as well as in soil-free bioreactors. The main goals were: (a) to identify and calibrate a kinetic model of TeCA cometabolism; (b) to select and characterize a TeCA-degrading bacterial consortium; (c) to compare the results obtained in slurry and in soil-free bioreactors. The results showed that 4 of the 5 tested aquifers contain TeCA-degrading bacteria, indicating that aerobic cometabolism is a potentially effective approach for TeCA-contaminated aquifers. In bioaugmentation tests, a TeCA-cometabolizing consortium developed in the slurry bioreactors induced a strong reduction of the lag-time for the onset of TeCA cometabolism. The soil-free tests yielded a satisfactory TeCA degradation performance, indicating that on-site soil-free bioreactors represent an interesting technical solution for the aerobic cometabolic bioremediation of CAH-contaminated groundwaters. The mineralization of the organic Cl was equal to about 97%. The prolonged TeCA biodegradation determined a progressive selection of the bacterial strains more effective in TeCA degradation and less affected by degradation product toxicity. The tested Michaelis–Menten-based kinetic model proved an effective tool to interpret the experimental data of TeCA aerobic cometabolism.

Pseudomonas pseudoalcaligenes KF707 is a polychlorinated biphenyls (PCBs) degrader, also tolerant to several toxic metals and metalloids. The work presented here examines for the first time the chemotactic response of P. pseudoalcaligenes KF707 to biphenyl and intermediates of the PCB biodegradation pathway in the presence and absence of metals. Chemotaxis analyses showed that biphenyl, benzoic acid and chlorobenzoic acids acted as chemoattractants for KF707 cells and that metal cations such as Ni2+ and Cu2+ strongly affected the chemotactic response. Toxicity profiles of various metals on KF707 cells grown on succinate or biphenyl as planktonic and biofilm were determined both in the presence and in the absence of PCBs. Notably, KF707 cells from both biofilms and planktonic cultures were tolerant to high amounts (up to 0.5 g L−1) of Aroclor 1242, a commercial mixture of PCBs. Together, the data show that KF707 cells are chemotactic and can form a biofilm in the presence of Aroclor 1242 and specific metals. These findings provide new perspectives on the effectiveness of using PCB-degrading bacterial strains in bioremediation strategies of metal-co-contaminated sites.

Polychlorinated biphenyls (PCBs) are ubiquitous persistent organic pollutants that can be co-metabolically biotransformed by biphenyl-utilizing bacteria. In this study, terminal-restriction fragment length polymorphism (T-RFLP) was applied to the substrate specificity-determining region of the 2,3-biphenyl dioxygenase encoding genes of a microbial community found in a PCB-polluted soil. Notably, both the total biphenyl/PCB-utilizing community and its members actively expressing the 2,3-biphenyl dioxygenase gene were analyzed. T-RFLP fingerprinting along with gene library construction allowed us not only to detect biphenyl dioxygenases related to the well characterized catabolic patterns of Pseudomonas pseudoalcaligenes KF707 and Burkholderia xenovorans LB400, but also to reveal novel environmental enzyme classes displaying amino acid substitutions that may be related to broader specificity and improved catalytic properties. Furthermore, space and time of sampling along with bioavailability conditions of different PCBs were considered possible sources of profile variability.

Tellurite (TeO3(2-)) is the most toxic and soluble oxyanion among tellurium (Te) compounds. The effects of the metalloid anion on the oxidative stress response of the obligate aerobe Pseudomonas pseudoalcaligenes KF707 were investigated. Cells treated with sub-lethal concentrations of TeO3(2-) showed neither adaptation to it nor cross-protection against oxidants such as 1,1'-4,4'-bipyridinium dichloride (paraquat, PQ2+), diazenedicarboxylic acid bis-N,N-dimethylamide (diamide), tert-butyl hydroperoxide (tBH) and hydrogen peroxide (H2O2). Notably, TeO3(2-) exerted a synergic effect on the toxicity of these latter oxidants. Tellurite was shown to decrease the cellular content of reduced thiols (RSH) with a consequent increase in the production of reactive oxygen species (ROS) and stimulation of the superoxide dismutase (SOD) activity. However, since the time course of ROS production by TeO3(2) (t1/2 > 30 min) was much slower than that with PQ2+ and/or diamide (t1/2

Anaerobically light-grown cells of Rhodobacter capsulatus B100 are highly resistant to the toxic oxyanion tellurite (TeO(3)(2-); minimal inhibitory concentration, 250 microg/ml). This study examines, for the first time, some structural and biochemical features of cells and plasma membrane fragments of this facultative phototroph grown in the presence of 50 microg of K(2)TeO(3) per ml. Through the use of transmission microscopy and X-ray microanalysis we show that several "needlelike" shaped granules of elemental tellurium are accumulated into the cytosol near the intracytoplasmic membrane system. Flash-spectroscopy, oxygen consumption measurements, and difference spectra analysis indicated that membrane vesicles (chromatophores) isolated from tellurite-grown cells are able to catalyze both photosynthetic and respiratory electron transport activities, although they are characterized by a low c-type cytochrome content (mostly soluble cytochrome c(2)). This feature is paralleled by a low cytochrome c oxidase activity and with an NADH-dependent respiration which is catalyzed by a pathway leading to a quinol oxidase (Qox) inhibited by high (millimolar) concentrations of cyanide (CN(-)). Conversely, membranes from R. capsulatus B100 cells grown in the absence of tellurite are characterized by a branched respiratory chain in which the cytochrome c oxidase pathway (blocked by CN(-) in the micromolar range) accounts for 35-40% of the total NADH-dependent oxygen consumption, while the remaining activity is catalyzed by the quinol oxidase pathway. These data have been interpreted to show that tellurite resistance of R. capsulatus B100 is characterized by the presence of a modified plasma-membrane-associated electron transport system.

A process of chloroform (CF) aerobic cometabolic biodegradation by a butane-growing consortium was studied for 354 days in a 2-m continuous-flow sand-filled reactor. The study was aimed at (a) investigating the oxygen/substrate pulsed injection as a tool to control the clogging of the porous medium, to attain a wide bioreactive zone and to reduce substrate inhibition on CF cometabolism; (b) developing a reliable model of CF cometabolism in porous media. While the continuous supply of butane rapidly led to the clogging of the porous medium due to excessive biomass growth, the testing of six types of oxygen/substrate pulsed feeding led to the identification of a feeding schedule capable to prevent aquifer clogging and to lead to the development of a long bioreactive zone and to satisfactory CF degradation performances. The tested model of aerobic cometabolism allowed a suitable interpretation of the experimental data as long as the ratio of CF degraded to butane consumed was ≤0.27 mg CF mg butane −1 . A long-term 1-D simulation of the best-performing schedule of pulsed oxygen/substrate supply extended to a 30-m aquifer length resulted in a 20-m bioreactive zone and in a 96% CF removal.

BACKGROUND: Bio-hydrogen production from organic residues is an attractive process that combines energy generation with waste treatment. This work describes hydrogen production from molasses and cheese whey by biofilm and suspended-cells of four hyperthermophilicThermotoga spp. For the best performing strain, a preliminary process optimization was performed. RESULTS: In experiments with glucose-fed T.neapolitana, HEPES was the best-performing buffer, whereas the highest H2 rate was obtained with the biofilm support exposing the highest specific surface. All the Thermotoga strains tested (T.neapolitana, T.maritima, T.naphtophila, T.petrophila) were able to produce H2 from glucose, molasses and cheese whey under both suspended- and attached-cell conditions. T.neapolitana was the best H2 producer with all three substrates. The best H2 production rate was higher on molasses (1.7 mmolH2 L −1 medium h −1 ) than on cheese whey (0.94 mmolH2 L −1 medium h −1 ), whereas the highestH2/substrateyieldsweresimilarforthetwosubstrates(2.95 molH2 mol −1 monosaccharide consumed onmolassesand2.50 molH2 mol −1 monosaccharide consumed on cheese whey). With both wastes, the progressive growth medium simplification allowed a drastic reduction of medium cost, without significant losses of process performance. CONCLUSION: Both molasses and cheese whey are suitable substrates for H2 production by suspended- and attached-cells of Thermotoga species. c � 2012 Society of Chemical Industry Supportinginformationmaybefoundintheonlineversionofthisarticle.

Chloroform (CF) is largely produced by both anthropogenic and natural sources. It is detected in ground- and surface-water sources and it represents the most abundant halocarbon in the atmosphere. Microbial CF degradation occurs under both aerobic and anaerobic conditions. Apart from a few reports describing the utilization of CF as a terminal electron acceptor during growth, CF degradation was mainly reported as a cometabolic process. CF aerobic cometabolism is supported by growth on short-chain alkanes (i.e. methane, propane, butane and hexane), aromatic hydrocarbons (i.e. toluene and phenol) and ammonia via the activity of monooxygenases operatively divided into different families. The main factors affecting CF cometabolism are i) the inhibition of CF degradation exerted by the growth substrate, ii) the need for reductant supply to maintain monooxygenase activity, and iii) the toxicity of CF degradation products. Under anaerobic conditions, CF degradation was mainly associated to the activity of methanogens, although some examples of CF-degrading sulfate-reducing, fermenting, and acetogenic bacteria are reported in the literature. Higher CF toxicity levels and lower degradation rates were shown by anaerobic systems in comparison to the aerobic ones. Applied, physiological and genetic aspects of microbial cometabolism of CF will be presented along with bioremediation perspectives.

Pseudomonas pseudoalcaligenes KF707 is a soil polychlorinated biphenyl (PCB) degrader, able to grow both planktonically and as a biofilm in the presence of various toxic metals and metalloids. Here we report the genome sequence (5,957,359 bp) of P. pseudoalcaligenes KF707, which provides insights into metabolic degradation pathways, flagellar motility, and chemotaxis.

This work focuses on chloroform (CF) cometabolism by a butane-grown aerobic pure culture (Rhodococcus aetherovorans BCP1) in continuous-flow biofilm reactors. The goals were to obtain preliminary information on the feasibility of CF biodegradation by BCP1 in biofilm reactors and to evaluate the applicability of the pulsed injection of growth substrate and oxygen to biofilm reactors. The attached-cell tests were initially conducted in a 0.165-L bioreactor and, then, scaled-up to a 1.772-L bioreactor. Glass cylinders were utilized as biofilm carriers. The continuous supply of growth substrate (butane), which led to the attainment of the highest CF degradation rate (8.4 mg(CF) day(-1) m (biofilm surface)(-2)), was compared with four schedules of butane and oxygen pulsed feeding. The pulsed injection technique allowed the attainment of a ratio of CF mass degraded per unit mass of butane supplied equal to 0.16 mg(CF) mg (butane)(-1), a value 4.4 times higher than that obtained with the continuous substrate supply. A procedure based on the utilization of integral mass balances and of average concentrations along the bioreactors resulted in a satisfactory match between the predicted and the experimental CF degradation performances, and can therefore be utilized to provide a guideline for optimizing the substrate pulsed injection schedule.

Summary Seventeen strains belonging to the genus Azospirillum were isolated from crop plant roots and characterized following routine morphological and physiological methods without obtaining a definite species assignment. DNA restriction pattern analysis was therefore performed on those strains and on 9 reference strains belonging to Azospirillum lipoferum, Azospirillum brasilense and Azospirillum amazonense. Fragments obtained with endonuclease BglII digestion were separated with PAGE and stained with silver nitrate. An internal standard was used to rescale the separation profiles, thereby permitting the comparison of samples from different gels. Each pattern was found to be unique, allowing the distinction of single strains. UPGMA analysis, yielding clusters of band patterns, was utilized to assign strains to a species. Restriction pattern analysis is therefore suggested for the routine identification of azospirilla.

An aerobic bacterial strain, named PB1, was microbiologically characterized and subjected to assays of cometabolic biodegradation of chlorinated aliphatic hydrocarbons (CAHs) aimed at (i) investigating its capacity to biodegrade vinyl chloride (VC), cis-1,2-dichloroethylene (cis-DCE), 1,1,2-trichloroethane (1,1,2-TCA), chloroform (CF) and 1,1,2,2-tetrachloroethane (1,1,2,2-TeCA); and (ii) evaluating the suitability of a kinetic model with inhibition and transformation product toxicity to describe CAH biodegradation by PB1. The strain proved to be closely related to the genus Rhodococcus. It biodegraded VC, cis-DCE, 1,1,2-TCA and CF via aerobic cometabolism on propane, but not 1,1,2,2-TeCA. CAH biodegradation by PB1 was satisfactorily described by the tested kinetic model. The maximum specific biodegradation rates were in the 1-11 micromol/mg protein/day range. The transformation capacities varied from 0.6 to 3 micromol/mg protein. Propane exerted a significant inhibition on both CF and cis-DCE biodegradation. CF, at 52 microM, did not inhibit propane utilization. An analysis of different inhibition models showed that cis-DCE inhibition on propane utilization was satisfactorily simulated with the competitive model, with an inhibition constant equal to 70% of the cis-DCE half-saturation constant. A final assay specifically aimed at validating the kinetic model and the verifying the estimates of the kinetic parameters yielded a satisfactory result. The results provide positive indications on the feasibility of utilizing strain PB1 for CAH biodegradation in aquifers and wastewaters.

The aerobic cometabolic biodegradation of a mixture of chlorinated aliphatic hydrocarbons (CAHs) including vinyl chloride (VC), cis - and trans -1,2-dichloroethylene ( cis -DCE, trans -DCE), trichloroethylene (TCE), 1,1,2-trichloroethane (1,1,2-TCA) and 1,1,2,2-tetrachloroethane (1,1,2,2-TeCA) was investigated at both 25 and 17 °C by means of bioaugmented and non-bioaugmented sediment-groundwater slurry microcosm tests. The goals of the study were (i) to study the long-term aerobic biodegradation of a CAH mixture including a high-chlorinated solvent (1,1,2,2-TeCA) generally considered non-biodegradable in aerobic conditions; (ii) to investigate the efficacy of bioaugmentation with two types of internal inocula obtained from the indigenous biomass of the studied site; (iii) to identify the CAH-degrading bacteria. VC, methane and propane were utilized as growth substrates. The non-bioaugmented microcosms were characterized, at 25 °C, by an average 18-day lag-time for the direct metabolism of VC (accompanied by the cometabolism of cis - and trans -DCE) and by long lag-times (36–264 days) for the onset of methane or propane utilization (associated with the cometabolism of the remaining CAHs). In the inoculated microcosms the lag-phases for the onset of growth substrate utilization and CAH cometabolism were significantly shorter (0–15 days at 25 °C). Biodegradation of the 6-CAH mixture was successfully continued for up to 410 days. The low-chlorinated solvents were characterized by higher depletion rates. The composition of the microbial consortium of a propane-utilizing microcosm was determined by 16s rDNA sequencing and phylotype analysis. To the best of our knowledge, this is the first study that documents the long-term aerobic biodegradation of 1,1,2,2-TeCA.

The ability of a Rhodococcus aetherovorans strain, BCP1, to grow on butane and to degrade chloroform in the 0-633 microM range (0-75.5 mg l(-1)) via aerobic cometabolism was investigated by means of resting-cell assays. BCP1 degraded chloroform with a complete mineralization of the organic Cl. The resulting butane and chloroform maximum specific degradation rates were equal to 118 and 22 micromol mg(protein)(-1)day(-1), respectively. Butane inhibition on chloroform degradation was satisfactorily interpreted by means of a model of competitive inhibition, with an inhibition constant equal to 38 % of the estimated butane half-saturation constant, whereas chloroform (at 11 microM) did not inhibit butane utilization. Acetylene (1,720 microM) induced an almost complete inactivation of the degradation of both butane and chloroform, indicating that the studied cometabolic process is mediated by a monooxygenase enzyme. BCP1 proved capable of degrading vinyl chloride and 1,1,2-trichloroethane, but not 1,2-trans-dichloroethylene. BCP1 could grow on the intermediates of the most common butane metabolic pathways and on the aliphatic hydrocarbons from ethane to n-heptane. After growth on n-hexane, it was able to deplete chloroform (13 microM) with a degradation rate higher than that obtained, at the same chloroform concentration, after growth on butane.

The focus of this microcosm study was to monitor the performances of 17 butane-utilizing microcosms during a long-term (100-250 days) aerobic cometabolic depletion of chloroform (CF). The depletion of the contaminant began after a lag-time variable between 0 and 23 days. All microcosms quickly reached a pseudo steady-state condition, in terms of biomass concentration (with an average of 9.3 x 106 CFU ml(-1)), chloroform depletion rate (5 micromol l(-1) d(-1)) and butane utilization rate (730 micromol l(-1) d(-1)). After about 100 days of CF depletion, a sudden 5- to 7-fold increase of the chloroform rate was observed in two microcosms, where the highest amount of contaminant had been depleted. In one of these high-performing microcosms, an experiment of chloroform depletion in the absence of butane resulted in the depletion of a surprisingly high amount of contaminant (765 micromolCF kg(-1) dry soil in 2 months) and in a marked selection of a single bacterial strain. Bioaugmentation assays conducted with the biomass selected in this microcosm and with a pure culture of the selected strain immediately resulted in very high chloroform depletion rates. Preliminary results of a study conducted with resting cells of the selected strain indicated that it can degrade chloroform concentrations up to 119 microM (14.2 mg l(-1)) without any sign of substrate toxicity, and that it is able to transform vinyl chloride and 1,1,2-trichloroethane.

The bioremediation of aged polychlorinated biphenyl (PCB)-contaminated soils is adversely affected by the low bioavailability of the pollutants. Randomly methylated-beta-cyclodextrins (RAMEB) were tested as a potential PCB-bioavailability-enhancing agent in the aerobic treatment of two aged-contaminated soils. The soils, contaminated by about 890 and 8500 mg/kg of Aroclor 1260 PCBs, were amended with biphenyl (4 g/kg), inorganic nutrients (to adjust their C:N ratio to 20:1), and variable amounts of RAMEB (0%, 0.5%, or 1.0% [w/w]) and treated in both aerobic 3-L solid-phase reactors and 1.5-L packed-bed loop reactors for 6 months. Notably, significant enhancement of the PCB biodegradation and dechlorination, along with a detectable depletion of the initial soil ecotoxicity, were generally observed in the RAMEB-treated reactors of both soils. RAMEB effects were different in the two soils, depending upon the treatment conditions employed, and generally increased proportionally with the concentration at which RAMEB was applied. RAMEB, which was slowly metabolized by the soil's aerobic microorganisms, was found to markedly enhance the occurrence of the indigenous aerobic, cultivable biphenyl-growing bacteria harboring genes homologous to those of two highly specialized PCB degraders (i.e., bphABC genes of Pseudomonas pseudoalcaligenes KF707 and bphA1A2A3A4BC1 genes of Rhodococcus globerulus P6) and chlorobenzoic acid-degrading bacteria as well as the occurrence of PCBs in the water phase of the soil reactors. These findings indicate that RAMEB enhanced the aerobic bioremediation of the two soils by increasing the bioavailability of PCBs and the occurrence of specialized bacteria in the soil reactors.

This study shows that the oxyanion tellurite TeO32- can be used as a tool to detect and quantify the release in soil microcosms of Pseudomonas pseudoalcaligenes KF707, a strain spontaneously resistant to tellurite with a minimal inhibitory concentration (MIC) of 150 μg ml-1. KF707 cells which carry the genes for degradation of a wide range of polychlorinated biphenyl congeners (PCBs) were used for inoculation of laboratory microcosms prepared with two different PCB-contaminated soils (Ci/s and Di/s) in the presence or absence of biphenyl as carbon source. In all microcosms supplemented with biphenyl, significant survival of strain KF707 was noted over a time period of 35 days; conversely, in microcosms containing Ci/s soil without biphenyl addition a rapid decrease in KF707 inoculated cells was observed. By comparing the number of inoculated KF707 cells with the number of indigenous bacteria growing on biphenyl (IBGB) of both Ci/s and Di/s microcosms, it could be concluded that the KF707/IBGB ratio is a relevant parameter in determining the fate of the added strain. The efficacy of potassium tellurite as a selective marker to monitor strain KF707 in laboratory microcosms was confirmed by ARDRA analyses of the 16S rDNA, while the isolated indigenous bacteria growing on biphenyl were identified as members of three different species of the genus Pseudomonas. We also report that in microcosms inoculated with KF707 cells in the absence of biphenyl, only low chlorinated biphenyls were degraded. © 2002 Éditions scientifiques et médicales Elsevier SAS. All rights reserved.