Role of heterotrophic bacteria in complete mineralization of trichloroethylene by Methylocystis sp. strain M

Assimilative and co-metabolic degradation of chloral hydrate by bacteria and their bioremediation potential

Although the bacterial degradation of chloral hydrate (CH) has been recognized for several decades, its degradation pathway by assimilation has not been demonstrated. In this paper, we report the isolation of the LF54 bacterial strain, which utilizes CH as its sole carbon and energy source. LF54 converted CH into trichloroethanol (TCAol), which was dehalogenated to dichloroethanol (DCAol), and CO(2) was detected as the end product. Another strain that we isolated, RS20, co-metabolized CH into TCAol. Our 16S rRNA gene sequencing and taxonomic analyses revealed that the LF54 and RS20 strains belong to the Pseudomonas and Arthrobacter genera, respectively. When the two strains were inoculated into soil microcosms, both degraded 0.3mM CH to undetectable levels (<0.01mM) within 5days. These results suggest that LF54 and RS20 could be used in the bioremediation of CH-contaminated environments.

Reductive Dechlorination of Trichloroethylene and Tetrachloroethylene under Aerobic Conditions in a Sediment Column

Biodegradation of trichloroethylene and tetrachloroethylene under aerobic conditions was studied in a sediment column. Cumulative mass balances indicated 87 and 90% removal for trichloroethylene and tetrachloroethylene, respectively. These studies suggest the potential for simultaneous aerobic and anaerobic biotransformation processes under bulk aerobic conditions.

Microbial community structure and trichloroethylene degradation in groundwater

Trichloroethylene (TCE) is a prevalent contaminant of groundwater that can be cometabolically degraded by indigenous microbes. Groundwater contaminated with TCE from a US Department of Energy site in Ohio was used to characterize the site-specific impact of phenol on the indigenous bacterial community for use as a possible remedial strategy. Incubations of14C-TCE-spiked groundwater amended with phenol showed increased TCE mineralization compared with unamended groundwater. Community structure was determined using DNA directly extracted from groundwater samples. This DNA was then analyzed by amplified ribosomal DNA restriction analysis. Unique restriction fragment length polymorphisms defined operational taxonomic units that were sequenced to determine phylogeny. DNA sequence data indicated that known TCE-degrading bacteria including relatives of Variovorax and Burkholderia were present in site water. Diversity of the amplified microbial rDNA clone library was lower in phenol-amended communities than in unamended groundwater (i.e., having Shannon–Weaver diversity indices of 2.0 and 2.2, respectively). Microbial activity was higher in phenol-amended ground water as determined by measuring the reduction of 2-(p-iodophenyl)-3(p-nitrophenyl)-5-phenyl tetrazolium chloride. Thus phenol amendments to groundwater correlated with increased TCE mineralization, a decrease in diversity of the amplified microbial rDNA clone library, and increased microbial activity.Key words: community structure, trichloroethylene, degradation, groundwater.

Bacterial populations occuring in a trichloroethylene-contaminated aquifer during methane injection

Soil core samples were obtained from a trichloroethylene (TCE)-contaminated aquifer before and after the start of methane biostimulation. DNA was extracted directly from the soil samples, and denaturing gradient gel electrophoresis (DGGE) was used to analyse bacterial 16S ribosomal DNA fragments that were PCR amplified from these DNA samples. This analysis consistently detected two phylotypes in the methane-injected samples. These phylotypes were closely related to Methylobacter and Methylomonas, both belonging to type I methanotrophs. A competitive DGGE analysis using Methylosinus trichosporium OB3b cells as an internal quantitative standard showed that these populations accounted for 10(8)-10(9) cells g(-1) soil. These results showed that type I methanotrophs formed a significant proportion of the bacterial community during methane biostimulation. The implications of this finding for TCE bioremediation were discussed.

Identification of intermediates of in vivo trichloroethylene oxidation by the membrane-associated methane monooxygenase

The rate and products of trichloroethylene (TCE) oxidation by Methylomicrobium album BG8 expressing membrane-associated methane monooxygenase (pMMO) were determined using 14C radiotracer techniques. [(14)C]TCE was degraded at a rate of 1.24 nmol (min mg protein)(-1) with the initial production of glyoxylate and then formate. Radiolabeled CO(2) was also found after incubating M. album BG8 for 5 h with [(14)C]TCE. Experiments with purified pMMO from Methylococcus capsulatus Bath showed that TCE could be mineralized to CO(2) by pMMO. Oxygen uptake studies verified that M. album BG8 could oxidize glyoxylate and that pMMO was responsible for the oxidation based on acetylene inactivation studies. Here we propose a pathway of TCE oxidation by pMMO-expressing cells in which TCE is first converted to TCE-epoxide. The epoxide then spontaneously undergoes HCl elimination to form glyoxylate which can be further oxidized by pMMO to formate and CO(2).

Aerobic degradation of 1,1,1-trichloroethane by Mycobacterium spp. isolated from soil

Two strains of 1,1,1-trichloroethane (TCA)-degrading bacteria, TA5 and TA27, were isolated from soil and identified as Mycobacterium spp. Strains TA5 and TA27 could degrade 25 and 75 mg. liter of TCA(-1) cometabolically in the presence of ethane as a carbon source, respectively. The compound 2,2,2-trichloroethanol was produced as a metabolite of the degradation process.

Bioremediation of trichloroethylene and cis-1,2-dichloroethylene-contaminated groundwater by methane-utilizing bacteria

Experimental studies on the bioremediation of groundwater contaminated with low concentration trichloroethylene (TCE) and cis1,2-dichloroethylene (DCE) were performed with two sets of bioreactors. Reactors No. 1 and No. 2 were operated without and with methane supplement, respectively. No inoculum was used. The concentrations of TCE and DCE in the effluent and the off gas from reactor No. 2 were much lower than those from reactor No. 1. When air and an H2O2 solution were supplied to reactor No. 2, concentrations of TCE and DCE in the effluent and the off gas were lower than the lowest detectable limit. The population of methane-utilizing bacteria in reactor No. 2 was 1,000 times higher than that in groundwater or in the effluent from reactor No. 1. These methane-utilizing bacteria were apparently attributable to the treatment of TCE.

The soluble methane monooxygenase gene cluster of the trichloroethylene-degrading methanotroph Methylocystis sp. strain M

In methanotrophic bacteria, methane is oxidized to methanol by the enzyme methane monooxygenase (MMO). The soluble MMO enzyme complex from Methylocystis sp. strain M also oxidizes a wide range of aliphatic and aromatic compounds, including trichloroethylene. In this study, heterologous DNA probes from the type II methanotroph Methylosinus trichosporium OB3b were used to isolate souble MMO (sMMO) genes from the type II methanotroph Methylocystis sp. strain M. sMMO genes from strain M are clustered on the chromosome and show a high degree of identity with the corresponding genes from Methylosinus trichosporium OB3b. Sequencing and phylogenetic analysis of the 16S rRNA gene from Methylocystis sp. strain M have confirmed that it is most closely related to the type II methanotroph Methylocystis parvus OBBP, which, unlike Methylocystis sp. strain M, does not possess an sMMO. A similar phylogenetic analysis using the pmoA gene, which encodes the 27-kDa polypeptide of the particulate MMO, also places Methylocystis sp. strain M firmly in the genus Methylocystis. This is the first report of isolation and characterization of methane oxidation genes from methanotrophs of the genus Methylocystis.

Engineering hybrid pseudomonads capable of utilizing a wide range of aromatic hydrocarbons and of efficient degradation of trichloroethylene

We constructed hybrid Pseudomonas strains in which the bphA1 gene (coding for a large subunit of biphenyl dioxygenase) is replaced with the todC1 gene (coding for a large subunit of toluene dioxygenase of Pseudomonas putida Fl) within chromosomal biphenyl-catabolic bph gene clusters. Such hybrid strains gained the novel capability to grow on a wide range of aromatic hydrocarbons, and, more interestingly, they degraded chloroethenes such as trichloroethylene and cis-1,2-dichloroethylene very efficiently.

Trichloroethylene degradation and mineralization by pseudomonads and Methylosinus trichosporium OB3b

To examine the trichloroethylene (C2HCl3)-degrading capability of five microorganisms, the maximum rate, extent, and degree of C2HCl3 mineralization were evaluated for Pseudomonas cepacia G4, Pseudomonas cepacia G4 PR1, Pseudomonas mendocina KR1, Pseudomonas putida F1, and Methylosinus trichosporium OB3b using growth conditions commonly reported in the literature for expression of oxygenases responsible for C2HCl3 degradation. By varying the C2HCl3 concentration from 5 microM to 75 microM, Vmax and Km values for C2HCl3 degradation were calculated as 9 nmol/(min mg protein) and 4 microM for P. cepacia G4, 18 nmol/(min mg protein) and 29 microM for P. cepacia G4 PR1, 20 nmol/(min mg protein) and 10 microM for P. mendocina KR1, and 8 nmol/(min mg protein) and 5 microM for P. putida F1. This is the first report of these Michaelis-Menten parameters for P. mendocina KR1, P. putida F1, and P. cepacia G4 PR1. At 75 microM, the extent of C2HCl3 that was degraded after 6 h of incubation with resting cells was 61%-98%; the highest degradation being achieved by toluene-induced P. mendocina KR1. The extent of C2HCl3 mineralization in 6 h (as indicated by concentration of chloride ion) was also measured and varied from 36% for toluene-induced P. putida F1 to 102% for M. trichosporium OB3b. Since C2HCl3 degradation requires new bio-mass, the specific growth rate (mu max) of each of the C2HCl3-degradation microorganisms was determined and varied from 0.080/h (M. trichosporium OB3b) to 0.864/h (P. cepacia G4 PR1).

Characterization of the methanotrophic bacterial community present in a trichloroethylene-contaminated subsurface groundwater site

Groundwater, contaminated with trichloroethylene (TCE) and tetrachloroethylene (PCE), was collected from 13 monitoring wells at Area M on the U.S. Department of Energy Savannah River Site near Aiken, S.C. Filtered groundwater samples were enriched with methane, leading to the isolation of 25 methanotrophic isolates. The phospholipid fatty acid profiles of all the isolates were dominated by 18:1 omega 8c (60 to 80%), a signature lipid for group II methanotrophs. Subsequent phenotypic testing showed that most of the strains were members of the genus Methylosinus and one isolate was a member of the genus Methylocystis. Most of the methanotroph isolates exhibited soluble methane monooxygenase (sMMO) activity. This was presumptively indicated by the naphthalene oxidation assay and confirmed by hybridization with a gene probe encoding the mmoB gene and by cell extract assays. TCE was degraded at various rates by most of the sMMO-producing isolates, whereas PCE was not degraded. Savannah River Area M and other groundwaters, pristine and polluted, were found to support sMMO activity when supplemented with nutrients and then inoculated with Methylosinus trichosporium OB3b. The maximal sMMO-specific activity obtained in the various groundwaters ranged from 41 to 67% compared with maximal rates obtained in copper-free nitrate mineral salts media. This study partially supports the hypothesis that stimulation of indigenous methanotrophic communities can be efficacious for removal of chlorinated aliphatic hydrocarbons from subsurface sites and that the removal can be mediated by sMMO.