Bioaugmentation of activated sludge by an indigenous 3-chloroaniline-degrading Comamonas testosteroni strain, I2gfp

Bioadsorber efficiency, design, and performance forecasting for alachlor removal

This study discusses a mathematical modeling and design protocol for bioactive granular activated carbon (GAC) adsorbers employed for purification of drinking water contaminated by chlorinated pesticides, exemplified by alachlor. A thin biofilm model is discussed that incorporates the following phenomenological aspects: film transfer from the bulk fluid to the adsorbent particles, diffusion through the biofilm immobilized on adsorbent surface, adsorption of the contaminant into the adsorbent particle. The modeling approach involved independent laboratory-scale experiments to determine the model input parameters. These experiments included adsorption isotherm studies, adsorption rate studies, and biokinetic studies. Bioactive expanded-bed adsorber experiments were conducted to obtain realistic experimental data for determining the ability of the model for predicting adsorber dynamics under different operating conditions. The model equations were solved using a computationally efficient hybrid numerical technique combining orthogonal collocation and finite difference methods. The model provided accurate predictions of adsorber dynamics for bioactive and non-bioactive scenarios. Sensitivity analyses demonstrated the significance of various model parameters, and focussed on enhancement in certain key parameters to improve the overall process efficiency. Scale-up simulation studies for bioactive and non-bioactive adsorbers provided comparisons between their performances, and illustrated the advantages of bioregeneration for enhancing their effective service life spans. Isolation of microbial species revealed that fungal strains were more efficient than bacterial strains in metabolizing alachlor. Microbial degradation pathways for alachlor were proposed and confirmed by the detection of biotransformation metabolites and byproducts using gas chromatography/mass spectrometry.

Bacterial community dynamics during biostimulation and bioaugmentation experiments aiming at chlorobenzene degradation in groundwater

A set of microcosm experiments was performed to assess different bioremediation strategies, i.e., biostimulation and bioaugmentation, for groundwater contaminated with chlorobenzenes. The biodegradative potential was stimulated either by the supply of electron acceptors (air, (NO3-), to increase the activity of the indigenous bacterial community, or by the addition of aerobic chlorobenzene-degrading bacteria (Pseudomonas putida GJ31, Pseudomonas aeruginosa RHO1, Pseudomonas putida F1deltaCC). Experiments were performed with natural groundwater of the aquifer of Bitterfeld, which had been contaminated with 1,2-dichlorobenzene (1,2-DCB), 1,4-dichlorobenzene (1,4-DCB), and chlorobenzene (CB). The microcosms consisted of airtight glass bottles with 800 mL of natural groundwater and were incubated under in situ temperature (13 degrees C). Behavior of the introduced strains within the indigenous bacterial community was monitored by fluorescent in situ hybridization (FISH) with species-specific oligonucleotides. Dynamics of the indigenous community and the introduced strains within the microcosms were followed by single-strand conformation polymorphism (SSCP) analysis of 16S rDNA amplicons obtained from total DNA of the microbial community. An indigenous biodegradation potential under aerobic as well as anaerobic denitrifying conditions was observed accompanied by fast and specific changes in the natural bacterial community composition. Augmentation with P. aeruginosa RHO1 did not enhance bio-degradation. In contrast, both P. putida GJ31 as well as P. putida F1deltaCC were capable of growing in groundwater, even in the presence of the natural microbial community, and thereby stimulating chlorobenzene depletion. P. putida GJ31 disappeared when the xenobiotics were depleted and P. putida F1deltaCC persisted even in the absence of CB. Detailed statistical analyses revealed that community dynamics of the groundwater microbiota were highly reproducible but specific to the introduced strain, its inoculum size, and the imposed physicochemical conditions. These findings could contribute to the design of better in situ bioremediation strategies for contaminated groundwater.

Strain-specific ureolytic microbial calcium carbonate precipitation

During a study of ureolytic microbial calcium carbonate (CaCO(3)) precipitation by bacterial isolates collected from different environmental samples, morphological differences were observed in the large CaCO(3) crystal aggregates precipitated within bacterial colonies grown on agar. Based on these differences, 12 isolates were selected for further study. We hypothesized that the striking differences in crystal morphology were the result of different microbial species or, alternatively, differences in the functional attributes of the isolates selected. Sequencing of 16S rRNA genes showed that all of the isolates were phylogenetically closely related to the Bacillus sphaericus group. Urease gene diversity among the isolates was examined by using a novel application of PCR-denaturing gradient gel electrophoresis (DGGE). This approach revealed significant differences between the isolates. Moreover, for several isolates, multiple bands appeared on the DGGE gels, suggesting the apparent presence of different urease genes in these isolates. The substrate affinities (K(m)) and maximum hydrolysis rates (V(max)) of crude enzyme extracts differed considerably for the different strains. For certain isolates, the urease activity increased up to 10-fold in the presence of 30 mM calcium, and apparently this contributed to the characteristic crystal formation by these isolates. We show that strain-specific calcification occurred during ureolytic microbial carbonate precipitation. The specificity was mainly due to differences in urease expression and the response to calcium.

Characterization of an autotrophic nitrogen-removing biofilm from a highly loaded lab-scale rotating biological contactor

In this study, a lab-scale rotating biological contactor (RBC) treating a synthetic NH(4)(+) wastewater devoid of organic carbon and showing high N losses was examined for several important physiological and microbial characteristics. The RBC biofilm removed 89% +/- 5% of the influent N at the highest surface load of approximately 8.3 g of N m(-2) day(-1), with N(2) as the main end product. In batch tests, the RBC biomass showed good aerobic and anoxic ammonium oxidation (147.8 +/- 7.6 and 76.5 +/- 6.4 mg of NH(4)(+)-N g of volatile suspended solids [VSS](-1) day(-1), respectively) and almost no nitrite oxidation (< 1 mg of N g of VSS(-1) day(-1)). The diversity of aerobic ammonia-oxidizing bacteria (AAOB) and planctomycetes in the biofilm was characterized by cloning and sequencing of PCR-amplified partial 16S rRNA genes. Phylogenetic analysis of the clones revealed that the AAOB community was fairly homogeneous and was dominated by Nitrosomonas-like species. Close relatives of the known anaerobic ammonia-oxidizing bacterium (AnAOB) Kuenenia stuttgartiensis dominated the planctomycete community and were most probably responsible for anoxic ammonium oxidation in the RBC. Use of a less specific planctomycete primer set, not amplifying the AnAOB, showed a high diversity among other planctomycetes, with representatives of all known groups present in the biofilm. The spatial organization of the biofilm was characterized using fluorescence in situ hybridization (FISH) with confocal scanning laser microscopy (CSLM). The latter showed that AAOB occurred side by side with putative AnAOB (cells hybridizing with probe PLA46 and AMX820/KST1275) throughout the biofilm, while other planctomycetes hybridizing with probe PLA886 (not detecting the known AnAOB) were present as very conspicuous spherical structures. This study reveals that long-term operation of a lab-scale RBC on a synthetic NH(4)(+) wastewater devoid of organic carbon yields a stable biofilm in which two bacterial groups, thought to be jointly responsible for the high autotrophic N removal, occur side by side throughout the biofilm.

Bioaugmentation as a tool to protect the structure and function of an activated-sludge microbial community against a 3-chloroaniline shock load

Bioaugmentation of bioreactors focuses on the removal of xenobiotics, with little attention typically paid to the recovery of disrupted reactor functions such as ammonium-nitrogen removal. Chloroanilines are widely used in industry as a precursor to a variety of products and are occasionally released into wastewater streams. This work evaluated the effects on activated-sludge reactor functions of a 3-chloroaniline (3-CA) pulse and bioaugmentation by inoculation with the 3-CA-degrading strain Comamonas testosteroni I2 gfp. Changes in functions such as nitrification, carbon removal, and sludge compaction were studied in relation to the sludge community structure, in particular the nitrifying populations. Denaturing gradient gel electrophoresis (DGGE), real-time PCR, and fluorescent in situ hybridization (FISH) were used to characterize and enumerate the ammonia-oxidizing microbial community immediately after a 3-CA shock load. Two days after the 3-CA shock, ammonium accumulated, and the nitrification activity did not recover over a 12-day period in the nonbioaugmented reactors. In contrast, nitrification in the bioaugmented reactor started to recover on day 4. The DGGE patterns and the FISH and real-time PCR data showed that the ammonia-oxidizing microbial community of the bioaugmented reactor recovered in structure, activity, and abundance, while the number of ribosomes of the ammonia oxidizers in the nonbioaugmented reactor decreased drastically and the community composition changed and did not recover. The settleability of the activated sludge was negatively influenced by the 3-CA addition, with the sludge volume index increasing by a factor of 2.3. Two days after the 3-CA shock in the nonbioaugmented reactor, chemical oxygen demand (COD) removal efficiency decreased by 36% but recovered fully by day 4. In contrast, in the bioaugmented reactor, no decrease of the COD removal efficiency was observed. This study demonstrates that bioaugmentation of wastewater reactors to accelerate the degradation of toxic chlorinated organics such as 3-CA protected the nitrifying bacterial community, thereby allowing faster recovery from toxic shocks.

Synergistic degradation of linuron by a bacterial consortium and isolation of a single linuron-degrading variovorax strain

The bacterial community composition of a linuron-degrading enrichment culture and the role of the individual strains in linuron degradation have been determined by a combination of methods, such as denaturing gradient gel electrophoresis of the total 16S rRNA gene pool, isolation and identification of strains, and biodegradation assays. Three strains, Variovorax sp. strain WDL1, Delftia acidovorans WDL34, and Pseudomonas sp. strain WDL5, were isolated directly from the linuron-degrading culture. In addition, subculture of this enrichment culture on potential intermediates in the degradation pathway of linuron (i.e., N,O-dimethylhydroxylamine and 3-chloroaniline) resulted in the isolation of, respectively, Hyphomicrobium sulfonivorans WDL6 and Comamonas testosteroni WDL7. Of these five strains, only Variovorax sp. strain WDL1 was able to use linuron as the sole source of C, N, and energy. WDL1 first converted linuron to 3,4-dichloroaniline (3,4-DCA), which transiently accumulated in the medium but was subsequently degraded. To the best of our knowledge, this is the first report of a strain that degrades linuron further than the aromatic intermediates. Interestingly, the rate of linuron degradation by strain WDL1 was lower than that for the consortium, but was clearly increased when WDL1 was coinoculated with each of the other four strains. D. acidovorans WDL34 and C. testosteroni WDL7 were found to be responsible for degradation of the intermediate 3,4-DCA, and H. sulfonivorans WDL6 was the only strain able to degrade N,O-dimethylhydroxylamine. The role of Pseudomonas sp. strain WDL5 needs to be further elucidated. The degradation of linuron can thus be performed by a single isolate, Variovorax sp. strain WDL1, but is stimulated by a synergistic interaction with the other strains isolated from the same linuron-degrading culture.

Toluene removal from waste air using a flat composite membrane bioreactor

In this report, gaseous toluene biodegradation results in a flat composite membrane reactor inoculated with Pseudomonas putida TVA8 are presented. Preliminary abiotic experiments showed that transport of toluene through the membrane was linearly and negatively correlated with the gas residence time (tau). During a 339-day biofiltration experiment, the influence of gas residence time (2-24 sec) and mass loading rate (B(v); 10-483 g x m(-3) h(-1)) on the toluene elimination capacity was investigated. A maximum elimination capacity (EC(max)) of 397 g x m(-3) h(-1) was achieved at tau = 24 sec and B(v) = 473 g x m(-3) h(-1). Expressed per unit membrane area, the EC(m,max) was 0.793 g x m(-2) h(-1), which is five times higher than results obtained with other membrane bioreactor experiments in the same range of loading rates. At low gas residence times, reactor performance was limited by mass transfer. Toluene concentration profiles along the membrane were measured for several biotic and abiotic conditions. For inlet concentrations (C(in)) up to 1 g x m(-3), more than 90% was eliminated at 15 cm from the reactor inlet. For C(in) > 1.65 g x m(-3), longer membranes are necessary to obtain these high removal efficiencies.

Bioaugmenting bioreactors for the continuous removal of 3-chloroaniline by a slow release approach

The survival and activity of microbial degradative inoculants in bioreactors is critical to obtain successful biodegradation of non- or slowly degradable pollutants. Achieving this in industrial wastewater reactors is technically challenging. We evaluated a strategy to obtain complete and stable bioaugmentation of activated sludge, which is used to treat a 3-chloroaniline (3-CA) contaminated wastewater in a lab-scale semi-continuous activated sludge system. A 3-CA metabolizing bacterium, Comamonas testosteroni strain I2, was mixed with molten agar and encapsulated in 4 mm diameter open-ended silicone tubes of 3 cm long. The tubes containing the immobilized bacteria represented about 1% of the volume of the mixed liquor. The bioaugmentation activity of a reactor containing the immobilized cells was compared with a reactor with suspended I2gfp cells. From day 25-30 after inoculation, the reactor with only suspended cells failed to completely degrade 3-CA because of a decrease in metabolic activity. In the reactors with immobilized cells, however, 3-CA continued to be removed. A mass balance indicated that ca. 10% of the degradation activity was due to the immobilized cells. Slow release of the growing embedded cells from the agar into the activated sludge medium, resulting in a higher number of active 3-CA-degrading I2 cells, was responsible for ca. 90% of the degradation. Our results demonstrate that this simple immobilization procedure was effective to maintain a 3-CA-degrading population within the activated sludge community.

Diversity of transconjugants that acquired plasmid pJP4 or pEMT1 after inoculation of a donor strain in the A- and B-horizon of an agricultural soil and description of Burkholderia hospita sp. nov. and Burkholderia terricola sp. nov

We examined the diversity of transconjugants that acquired the catabolic plasmids pJP4 or pEMT1, which encode degradation of 2,4-dichlorophenoxyacetic acid (2,4-D), in microcosms with agricultural soil inoculated with a donor strain (Dejonghe, W., Goris, J., El Fantroussi, S., Höfte, M., De Vos, P., Verstraete, W., and Top, E. M. Appl. Environ. Microbiol. 2000, p. 3297-3304). Using repetitive element PCR fingerprinting, eight different rep-clusters and six separate isolates could be discriminated among 95 transconjugants tested. Representative isolates were identified using 16S rDNA sequencing, cellular fatty acid analysis, whole-cell protein analysis and/or DNA-DNA hybridisations. Plasmids pJP4 and pEMT1 appeared to have a similar transfer and expression range, and were preferably acquired and expressed in soil by indigenous representatives of Ralstonia and Burkholderia. Two rep-clusters were shown to represent novel Burkholderia species, for which the names Burkholderia hospita sp. nov. and Burkholderia terricola sp. nov. are proposed. When easily degradable carbon sources were added together with the plasmid-bearing donor strain, also a significant proportion of Stenotrophomonas maltophilia isolates were found. The transconjugant collections isolated from A- (0-30 cm depth) and B-horizon (30-60 cm depth) soil were similar, except for B. terricola transconjugants, which were only isolated from the B-horizon.

Reductive deamination as a new step in the anaerobic microbial degradation of halogenated anilines

In this paper we report the isolation and characterization of an anaerobic enrichment culture as well as of a Rhodococcus sp. strain 2 capable of degrading 3,4-dihaloanilines under nitrate reducing conditions. Using mass spectrometry several of the intermediates formed in the process of 3,4-dichloroaniline conversion were identified. Most interesting is the observation of reductive deamination and the formation of 1,2-dichlorobenzene as one of the intermediates. Using 19F NMR and fluorinated 3,4-dihaloaniline model substrates it was corroborated that reductive deamination of the anilines to give dihalobenzene intermediates represents a new initial step in the anaerobic microbial degradation of these halogenated anilines.

Microorganisms relevant to bioremediation

Naturally occurring microbial consortia have been utilized in a variety of bioremediation processes. Recent developments in molecular microbial ecology offer new tools that facilitate molecular analyses of microbial populations at contaminated and bioremediated sites. Information provided by such analyses aids in the evaluation of the effectiveness of bioremediation and the formulation of strategies that might accelerate bioremediation.

Genetic diversity among 3-chloroaniline- and aniline-degrading strains of the Comamonadaceae

We examined the diversity of the plasmids and of the gene tdnQ, involved in the oxidative deamination of aniline, in five bacterial strains that are able to metabolize both aniline and 3-chloroaniline (3-CA). Three strains have been described and identified previously, i.e., Comamonas testosteroni I2 and Delftia acidovorans CA28 and BN3.1. Strains LME1 and B8c were isolated in this study from linuron-treated soil and from a wastewater treatment plant, respectively, and were both identified as D. acidovorans. Both Delftia and Comamonas belong to the family Comamonadaceae. All five strains possess a large plasmid of ca. 100 kb, but the plasmids from only four strains could be transferred to a recipient strain by selection on aniline or 3-CA as a sole source of carbon and/or nitrogen. Plasmid transfer experiments and Southern hybridization revealed that the plasmid of strain I2 was responsible for total aniline but not 3-CA degradation, while the plasmids of strains LME1 and B8c were responsible only for the oxidative deamination of aniline. Several transconjugant clones that had received the plasmid from strain CA28 showed different degradative capacities: all transconjugants could use aniline as a nitrogen source, while only some of the transconjugants could deaminate 3-CA. For all four plasmids, the IS1071 insertion sequence of Tn5271 was found to be located on a 1.4-kb restriction fragment, which also hybridized with the tdnQ probe. This result suggests the involvement of this insertion sequence element in the dissemination of aniline degradation genes in the environment. By use of specific primers for the tdnQ gene from Pseudomonas putida UCC22, the diversity of the PCR-amplified fragments in the five strains was examined by denaturing gradient gel electrophoresis (DGGE). With DGGE, three different clusters of the tdnQ fragment could be distinguished. Sequencing data showed that the tdnQ sequences of I2, LME1, B8c, and CA28 were very closely related, while the tdnQ sequences of BN3.1 and P. putida UCC22 were only about 83% identical to the other sequences. Northern hybridization revealed that the tdnQ gene is transcribed only in the presence of aniline and not when only 3-CA is present.

Use of green fluorescent protein and luciferase biomarkers to monitor survival and activity of Arthrobacter chlorophenolicus A6 cells during degradation of 4-chlorophenol in soil

The recently isolated novel species Arthrobacter chlorophenolicus A6 is capable of growth on and degradation of high concentrations of 4-chlorophenol (up to 350 microg ml(-1)) as the sole carbon and energy source. This strain shows promise for bioremediation of environmental sites contaminated with high levels of chlorophenols. In this study, green fluorescent protein (gfp) or luciferase (luc) genes were used as biomarkers for monitoring cell number and activity, respectively, during degradation of 4-chlorophenol by A. chlorophenolicus cells. The individual marked strains, Arthrobacter chlorophenolicus A6L (luc-tagged) and Arthrobacter chlorophenolicus A6G (gfp-tagged), were monitored during degradation of 250 microg ml(-1) 4-chlorophenol in pure culture and 175 microg g(-1) 4-chlorophenol in soil microcosms. Both gene-tagged strains were capable of cleaning up the contaminated soil during 9 d incubation. During the bioremediation experiments, the luc-tagged cells were monitored using luminometry and the gfp-tagged cells using flow cytometry, in addition to selective plate counting for both strains. The cells remained at high population levels in the soil (evidenced by GFP-fluorescent cell counts) and the A. chlorophenolicus A6L population was metabolically active (evidenced by luciferase activity measurements). These results demonstrate that the Arthrobacter chlorophenolicus A6 inoculum is effective for cleaning-up soil containing high concentrations of 4-chlorophenol.