Degradation potential and pathways of methylcyclohexane by bacteria derived from Antarctic surface water.

Cycloalkanes pose a tremendous environmental risk due to their high concentration in petroleum hydrocarbons and hazardous effects to organisms. Numerous studies have documented the biodegradation of acyclic alkanes and aromatic hydrocarbons. However, insufficient attention has been paid to studies on the microbial degradation of cycloalkanes, which might be closely linked to psychrophilic microbes derived from low-temperature habitats. Here we show that endemic methylcyclohexane (MCH, an abundant cycloalkane species in oil) consumers proliferated in seawater samples derived from the Antarctic surface water (AASW). The MCH-consuming bacterial communities derived from AASW exhibited a distinct species composition compared with their counterparts derived from other cold-water habitats. We also probed Colwellia and Roseovarius as the key active players in cycloalkane degradation by dilution-to-extinction-based incubation with MCH as sole source of carbon and energy. Furthermore, we propose two nearly complete MCH degradation pathways, lactone formation and aromatization, concurrently in the high-quality metagenome-assembled genomes of key MCH consumer Roseovarius. Overall, we revealed that these Antarctic microbes might have strong interactions that enhance the decomposition of more refractory hydrocarbons through complementary degradation pathways.

Methanogenic biodegradation of iso-alkanes and cycloalkanes during long-term incubation with oil sands tailings.

Microbes indigenous to oil sands tailings ponds methanogenically biodegrade certain hydrocarbons, including n-alkanes and monoaromatics, whereas other hydrocarbons such as iso- and cycloalkanes are more recalcitrant. We tested the susceptibility of iso- and cycloalkanes to methanogenic biodegradation by incubating them with mature fine tailings (MFT) collected from two depths (6 and 31 m below surface) of a tailings pond, representing different lengths of exposure to hydrocarbons. A mixture of five iso-alkanes and three cycloalkanes was incubated with MFT for 1700 d. Iso-alkanes were completely biodegraded in the order 3-methylhexane > 4-methylheptane > 2-methyloctane > 2-methylheptane, whereas 3-ethylhexane and ethylcyclopentane were only partially depleted and methylcyclohexane and ethylcyclohexane were not degraded during incubation. Pyrosequencing of 16S rRNA genes showed enrichment of Peptococcaceae (Desulfotomaculum) and Smithella in amended cultures with acetoclastic (Methanosaeta) and hydrogenotrophic methanogens (Methanoregula and Methanoculleus). Bioaugmentation of MFT by inoculation with MFT-derived enrichment cultures reduced the lag phase before onset of iso-alkane and cycloalkane degradation. However, the same enrichment culture incubated without MFT exhibited slower biodegradation kinetics and less CH4 production, implying that the MFT solid phase (clay minerals) enhanced methanogenesis. These results help explain and predict continued emissions of CH4 from oil sands tailings repositories in situ.

Novel indole-2-carboxamide and cycloalkeno[1,2-b]indole derivatives. Structure-activity relationships for high inhibition of human LDL peroxidation.

Series of indole-2-carboxamide and cycloalkeno[1,2-b]indole derivatives were synthesized and evaluated in order to determine the necessary structural requirements for a high inhibition of human LDL copper-induced peroxidation. Various modulations were systematically performed on the indole and cycloalkeno[1,2-b]indole nuclei as well as on the carboxamide moiety. The best compounds (3c, 3e, 7c, 7f, 7h, 7g, and 7o) are between 5 and 30 times more active than probucol itself. Two of these compounds (3c and 7o) were selected for complementary in vitro and in vivo investigations, which have shown additional properties of interest for the treatment and the prevention of atherosclerosis injuries. Compound 3c was found to have some antiinflammatory properties while compound 7o was proved to protect endothelial cells from the direct cytotoxicity of oxidized LDL with some additional calcium channel blocking properties.

Beyond TPH: health-based evaluation of petroleum hydrocarbon exposures.

The term "total petroleum hydrocarbons" (TPH) is a widely used, but loosely defined, parameter quantified by a number of different methodologies for expressing the aggregate amount of petroleum hydrocarbon compounds (PHCs) in a sample. Because of the shortcomings associated with comparing data from different methods, and the difficulty of assessing potential toxicities of complex mixtures of hydrocarbons, a new approach at more fully and explicitly defining the PHC composition of samples and predicting human noncancer health risks from those exposures has been developed. This new approach is the subject of this paper. This method can be used to perform site-specific risk assessments or to develop health-based cleanup standards for petroleum hydrocarbons. The technique divides the broad chemical classes of PHC (i.e., saturated versus unsaturated) into subgroups of compounds based on numbers of carbon atoms in the compounds within each subgroup. The mass of compounds in each subgroup is then translated into discrete estimates of health risk for specified exposure scenarios. The subgroups were identified from qualitative and quantitative changes in the nature of noncancer toxicities recorded in the literature. For saturated compounds, toxicity changes as carbon chain length increases (measured by numbers of carbon atoms). A "reference compound" was chosen for each range of compounds, usually because its toxicity was relatively well characterized. A published oral reference dose (RfD) was identified for these compounds, or in the absence of a published value, an oral dose-response value was developed from available toxicity information. For saturated PHCs (alkanes, cycloalkanes, and isoalkanes) the subgroups' reference compounds and assigned toxicity value used are C5 to C8 (n-hexane, 0.06 mg/kg/day); C9 to C18 (n-nonane, 0.6 mg/kg/day); and C19 to C32 (eicosane, 6.0 mg/kg/day). For unsaturated compounds (aromatics), one reference RfD was identified for all compounds: C9 through C32 (pyrene, 0.03 mg/kg/day). Dependent upon the analytical technique used for separation of compounds, the unsaturated alkenes may be grouped and subsequently quantified with either the saturate or unsaturate groups. The implications of possible association with either group and contributions to risk estimates are probably not significant. Alkenes make up a small fraction of most fuel products, and they bear structural similarity to the alkanes and are not particularly toxicologically active. If grouped analytically with the aromatics the alkene contribution to toxicity estimates would likely be minor and not be an underestimate of its true toxicity. The mass of PHC in each segment of a chromatogram is quantified and converted to a medium-specific concentration which is then entered into standard medium intake equations to arrive at a daily dose of PHC. This dose is then used with the toxicity value identified for the particular segment of the chromatogram to derive a hazard quotient. The quotients can then be summed across fractions to yield a total hazard index. The noncancer health risks from the aromatics benzene, toluene, and xylenes are evaluated separately using standard risk assessment techniques.

Biodegradation rates of components of petroleum.

Rates of microbial biodegradation of components of South Louisiana crude oil were determined by computer analysis of data obtained from computerized mass spectrometry. Total residue of the oil decreased exponentially with time, with maximum decrease noted at logarithmic phase, whereas asphaltenes and resins increased at the logarithmic phase of growth. Saturates decreased continuously during growth. Microbial degradation of components of crude oil was concluded to be a dynamic process.

The oxidation of D-quinate and related acids by Acetomonas oxydans.

1. Growing cells of a small number of strains of Acetomonas oxydans oxidized d-quinate to 5-dehydroquinate. 2. d-Shikimate was oxidized to 4,5-dihydroxy-3-oxocyclohex-1-ene-1-carboxylate (3-dehydroshikimate, formerly 5-dehydroshikimate). 3. d-Dihydroshikimate was oxidized to the corresponding 5-dehydro compound, but epidihydroshikimate oxidation by growing cells was not observed. 4. Cell-free extracts oxidized d-quinate to 5-dehydroquinate with the consumption of the stoicheiometric amount of oxygen, but oxidation of shikimate and dihydroshikimate did not go to completion. 5. Oxidation of quinate was brought about by a constitutive particulate enzyme probably localized in the cytoplasmic membrane. No evidence was found for the participation of NAD, NADP or free flavine compounds in electron transport, but the system was cytochrome-linked.