Phospholipid Furan Fatty Acids and Ubiquinone-8: Lipid Biomarkers That May Protect Dehalococcoides Strains from Free Radicals

Abstract

Dehalococcoides species have a highly restricted lifestyle and are only known to derive energy from reductive dehalogenation reactions. The lipid fraction of two Dehalococcoides isolates, strains BAV1 and FL2, and a tetrachloroethene-to-ethene-dechlorinating Dehalococcoides-containing consortium were analyzed for neutral lipids and phospholipid fatty acids. Unusual phospholipid modifications, including the replacement of unsaturated fatty acids with furan fatty acids, were detected in both Dehalococcoides isolates and the mixed culture. The following three furan fatty acids are reported as present in bacterial phospholipids for the first time: 9-(5-pentyl-2-furyl)-nonanoate (Fu18:26), 9-(5-butyl-2-furyl)-nonanoate (Fu17:25), and 8-(5-pentyl-2-furyl)-octanoate (Fu17:26). The neutral lipids of the Dehalococcoides cultures contained unusually large amounts of benzoquinones (i.e., ubiquinones [UQ]), which is unusual for anaerobes. In particular, the UQ-8 content of Dehalococcoides was 5-to 20-fold greater than that generated in aerobically grown Escherichia coli cultures relative to the phospholipid fatty acid content. Naphthoquinone isoprenologues (MK), which are often found in anaerobically grown bacteria and archaea, were also detected. Dehalococcoides shows a difference in isoprenologue pattern between UQ-8 and MK-5 that is atypical of other bacteria capable of producing both quinone types. The difference in UQ-8 and MK-5 isoprenologue patterns strongly suggests a special function for UQ in Dehalococcoides, and Dehalococcoides may utilize structural modifications in its lipid armamentarium to protect against free radicals that are generated in the process of reductive dechlorination.Tetrachloroethene (PCE) and trichloroethene (TCE) are ideal solvents for degreasing and dry cleaning, and their widespread use has led to massive groundwater pollution. Many impacted subsurface environments are cocontaminated with more readily degradable petroleum hydrocarbons at many military sites or with starch at dry-cleaning sites. Microbes readily utilize aerobically degradable substrates, thus depleting oxygen in the groundwater and inducing anaerobiosis. Biotic and abiotic processes acting on these chlorinated solvents facilitate the formation and accumulation of toxic intermediates such as the dichloroethenes (DCEs) and the human carcinogen vinyl chloride (VC). Of the 1,430 contaminated sites listed on the U.S. EPA National Priorities List, 64% contain TCE, 54% contain PCE, and 35% contain VC (51).A variety of subsurface bacteria are capable of anaerobic reductive dehalogenation, which represents the initial attack on these chlorinated solvents (43). Sulfate-reducing and acetogenic bacteria as well as methanogenic archaea can fortuitously catalyze reductive dehalogenation by free or enzymebound, metal ion-containing, heat-stable tetrapyrroles (9). Calculations of redox potentials for corresponding Cl-alkyl/ alkyl couples range from ϩ250 to ϩ487 mV, suggesting that chloroorganic compounds are favorable electron acceptors (7)....

Dehalogenimonas lykanthroporepellens gen. nov., sp. nov., a reductively dehalogenating bacterium isolated from chlorinated solvent-contaminated groundwater

“…T contained large proportions of C 16 : 1 v9c (23.0 and 23.2 %, respectively), significant concentrations of summed feature 5 (one or more of C 18 : 2 v6c, C 18 : 2 v9c and anteiso-C 18 : 0 ) (7.9 and 6.5 %, respectively) and summed feature 3 (one or more of C 16 : 1 v7c, C 16 : 1 v6c and iso-C 15 : 0 3-OH), while these were not detected in strain BAV1 or FL2 (White et al, 2005). 10-Methyl C 16 : 0 made up a large proportion of the cellular fatty acids in 'Dehalococcoides' sp.…”

“…10-Methyl C 16 : 0 made up a large proportion of the cellular fatty acids in 'Dehalococcoides' sp. BAV1 and FL2 (21.3 and 24.4 %, respectively;White et al, 2005) but was not detected in strain BL-DC-8 or BL-DC-9…”

“…C 18 : 1 v9c comprised a major fraction of the cellular fatty acids in strains BL-DC-8 and BL-DC-9 T (21.8 and 23.4 %, respectively) but was present in only trace amounts in 'Dehalococcoides' strains BAV1 and FL2 (0.4 and 0.5 %, respectively; White et al, 2005).…”

Synthesis and scavenging role of furan fatty acids

“…This result was somewhat surprising because the conditions used to produce 1 O 2 are known to be sufficient to increase σ E activity (19,20) so we expected to see accumulation of 19Fu-FA. 1 O 2 can directly oxidize furan moieties and produce fatty acyl radicals from unsaturated fatty acids so it has been proposed that Fu-FAs can act as a scavenger for this and other ROS (14,15,34,35). Thus, the failure to observe alterations of the fatty-acid content when wild-type cells were exposed to 1 O 2 could reflect the ability of 19Fu-FA to scavenge this ROS or products of its action on bilayer constituents.…”

Biodiversity of Dehalorespiring Bacteria with Special Emphasis on Polychlorinated Biphenyl/Dioxin Dechlorinators

“…Methods for the enrichment and cultivation of "Dehalococcoides" as well as other reductively dechlorinating bacteria have been described in detail by Löf-fler et al 82) . One of the most striking observations on the properties of "Dehalococcoides" is that the lipid fraction of two "Dehalococcoides" isolates, strains BAV1 and FL2, and a PCE-toethene-dechlorinating "Dehalococcoides"-containing consortium contained unusual phospholipid modifications, including furan fatty acids, and large amounts of ubiquinone-8 131) . Smaller amounts of menaquinone-5 were also found.…”