Phospholipid, ester‐linked fatty acid profiles showed changes in benthic prokaryotic community structure reflecting culture manipulations that were both quantitative and statistically significant. Fatty acid structures, including the position and cis/trans geometry of double bonds, were chemically verified by GC/MS after appropriate derivatization. The fatty acid profiles of independent flasks showed reproducible shifts when manipulated identically and significant differences when manipulated with different treatments. The absence of polyunsaturated fatty acids indicated that the consortia were predominantly prokaryotic. The prokaryotic consortia of different treatments could be differentiated by the proportions of cyclopropyl fatty acids and the proportions and geometry of monounsaturated fatty acids.

The extractable ester‐linked and the lipopolysaccharide (LPS) normal and hydroxy fatty acids of the methylotrophic bacteria Methylosinus trichosporium 0B3B, Methylobacterium organophilum XX, grown on methane and methanol, Mb. organophilum RG and Methylomonas sp. were analysed by capillary gas chromotography‐mass spectrometry (GC‐MS). Precise monounsaturated double bond position and geometry was determined by GC‐MS analysis of the derivatized fatty acids. The three species were readily distinguished based on the extractable fatty acid and LPS hydroxy acid profiles. Type I and Type II methylotrophs can be separated based on the presence of 16‐carbon and 18‐carbon monoenoic fatty acids in the two groups of organisms, respectively. Relatively novel components, 18: 1ω8c, 18: 1ω8t, 18: 1ω7t and 18: 1ω6c were present in Ms. trichosporium, and 16: 1ω8c, 16: 1ω8t, 16: 1ω7t, 16: 1ω5c and 16: 1ω5t were detected in Methylomonas sp. These specific lipids may be used, together with other components, as signatures for these methylotrophic bacteria in manipulated laboratory and environmental samples.

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The phospholipid ester-linked normal and lipopolysaccharide layer hydroxy fatty acids from microbes in a natural gas (85% methane)-stimulated soil column capable of degrading halogenated hydrocarbons were analyzed in detail by capillary column GC-MS. Microbial biomass, calculated from phospholipid fatty acid (PLFA) concentrations to be 5.6 x lo9 bacteria/g (dry weight), was greater in the hydrocarbon-degrading column than in either an azide-inhibited soil column or an untreated surface soil. Microbial community structure information, using GC-MS analysis of derivatized monounsaturated PLFA, indicated that the major component (16 to 28%) of the PLFA in the hydrocarbon-degrading column was the PLFA 18:lAlOc. This novel PLFA has been reported as a major component in type I1 methanotrophs. The high relative proportions of CIS components relative to CI6 fatty acids indicated that type I1 rather than type I methanotrophs were the most abundant microbial flora present in the active soil column. Fatty acids from other bacterial groups and microeukaryotes also were detected in the hydrocarbon-degrading soil column. Differences between the relative proportions of these metabolic groups of microorganisms were quantified and compared among the three soils analyzed. Based on these differences, the potential exists to use these methods to monitor shifts in microbial biomass and community structure in aquifers where indigenous bacteria are stimulated to biotransform pollutant compounds.

Degradation rates of benzene, p-xylene, naphthalene, and o-dichlorobenzene have been measured in a heterogeneous, unconfined aquifer during a pulse injection experiment at Columbus Air ForceBase, Columbus, Mississippi. Dissolved oxygen in the pulse plume maintained aerobic conditions. Degradation kinetics calculated from the complete field data set were approximately first order with the following rate constants: benzene, 0.0070 d-l; p-xylene, 0.0107 d -•; naphthalene, 0.0064 d -l; and o-dichlorobenzene, 0.0046 d-1. Reaction rates were also calculated from a near-field subset of the data using a model based on the hydrologic characteristics of the aquifer. Shapes of the degradation rate curves were consistent with microbial degradation processes. Maximum degradation rates obtained are presumed to be characteristic of the microbial population metabolism. Carbon 14-1abeled p-xylene was included in the injection solution to permit detection of degradation products. This technique is suggested for future field experiments, because it distinguishes solute degradation from solute losses by sorption and evaporation and allows mass balance to be demonstrated throughout the course of the reaction in the aquifer.