Polaromonas sp. JS666

Draft genome sequencing of chlorinated-alkene-degrading
Polaromonas strain JS666

Basic facts about, importance of, and motivation for sequencing JS666:

Polaromonas strain JS666 (ATCC No. BAA-500), a member of the family Comamonadaceae in the beta-proteobacteria, is a novel, aerobic, cis-dichloroethene (cDCE)-assimilating organism with optimum growth at 20-25¾C (2). Strain JS666 is closely related to the Antarctic marine isolate Polaromonas vacuolata (2). Significant phenotypic differences between strain JS666 and Polaromonas vaculota exist. For example, Polaromonas vaculota strains are white, motile, have gas vacuoles and a temperature optimum around 4 degrees C (4). JS666, on the other hand, is yellow, non-motile, devoid of vacuoles, and is not psychrophilic. The substantial phylogenetic distance from other known aerobic alkene-assimilating bacteria suggests a novel biochemistry for cDCE oxidation.

Strain JS666 is the only aerobic organism known to use cDCE for energy and growth. cDCE is a common groundwater contaminant (8) derived mainly from incomplete anaerobic reductive dechlorination of the widely used chlorinated solvents tetrachloroethene and trichloroethene (3, 6). The toxicity and suspected carcinogenicity of cDCE qualifies it as an EPA priority pollutant, and its presence in groundwater above concentrations of 70 ppb is considered an unacceptable hazard to human health and the environment. Since growth-coupled oxidation of cDCE does not appear to be common at field sites, JS666 is a prime candidate for bioaugmentation at sites where cDCE has migrated into aerobic zones.

In addition to the ability to degrade cDCE for growth, JS666 is capable of transforming (though not growing upon) trans-1,2-dichloroethene (tDCE), TCE, VC, 1,2-dichloroethane (1,2-DCA) and ETH (2). ETH is converted to epoxyethane by cDCE-grown JS666 cultures, but not in succinate-grown JS666 cultures, suggesting the a cDCE-inducible monooxygenase participates in the cDCE pathway (2). Pulsed Field Gel Electrophoresis (PFGE) experiments suggest that two large plasmids (approximately 340 and 360 kb) are present in JS666. Further PFGE experiments suggest that the plasmids have a linear topology. Additional work is required to determine if either of the plasmids is associated with cDCE oxidation.

Recently, a Polaromonas was reported to be the organism responsible for in situ biodegradation of naphthalene at a coal-tar-contaminated site (5). Closely related strains have also been found recently in a variety of contaminated sites (1, 7, 9), but their roles are unknown. The recent isolation of the above strains suggests that members of the genus Polaromonas play a major role in the subsurface degradation of environmental contaminants that has been overlooked to date because of an emphasis on mesophilic bacteria.


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