Membrane Lipids as Indicators for Viable Bacterial Communities Inhabiting Petroleum Systems.

Microbial activity in petroleum reservoirs has been implicated in a suite of detrimental effects including deterioration of petroleum quality, increases in oil sulfur content, biofouling of steel pipelines and other infrastructures, and well plugging. Here, we present a biogeochemical approach, using phospholipid fatty acids (PLFAs), for detecting viable bacteria in petroleum systems. Variations within the bacterial community along water flow paths (producing well, topside facilities, and injection well) can be elucidated in the field using the same technique, as shown here within oil production plants in the Molasse Basin of Upper Austria. The abundance of PLFAs is compared to total cellular numbers, as detected by qPCR of the 16S rDNA gene, to give an overall comparison between the resolutions of both methods in a true field setting. Additionally, the influence of biocide applications on lipid- and DNA-based quantification was investigated. The first oil field, Trattnach, showed significant PLFA abundances and cell numbers within the reservoir and topside facilities. In contrast, the second field (Engenfeld) showed very low PLFA levels overall, likely due to continuous treatment of the topside facilities with a glutaraldehyde-based antimicrobial. In comparison, Trattnach is dosed once per week in a batch fashion. Changes within PLFA compositions across the flow path, throughout the petroleum production plants, point to cellular adaptation within the system and may be linked to shifts in the dominance of certain bacterial types in oil reservoirs versus topside facilities. Overall, PLFA-based monitoring provides a useful tool to assess the abundance and high-level taxonomic diversity of viable microbial populations in oil production wells, topside infrastructure, pipelines, and other related facilities.

Characterization of complex assemblages of organic acids in geological samples by negative electrospray ionization mass spectrometry using a double-focusing magnetic sector field mass spectrometer.

Four different geological sample types (a crude oil, a crude oil asphaltene, a reservoir core extract and a reservoir core asphaltene) have been characterized by negative ionization electrospray mass spectrometry at low and high mass resolution using a double-focusing magnetic sector field mass spectrometer. The mass range, shape of the spectra and the signal distribution of the acidic constituents as well as the average molecular weights, the total ion abundance and signal intensity in the spectra were compared for the different sample types. Nominal mass classes have been evaluated and Kendrick mass plots were generated in order to identify homologous series. For the crude oil sample, accurate mass assignments were made by high-resolution double-focusing magnetic sector field mass spectrometry (DFMSFMS) and were compared with those obtained by negative ion electrospray ionization (ESI) Fourier transform ion cyclotron resonance mass spectrometry (FTICRMS). With both instrument types, compounds with the molecular composition C(n)H(2n+z)O(2), among which carboxylic acids predominated, were the main acidic compound class detectable in negative ESI mass spectra. Good agreement was achieved for the double bond class distribution and the carbon number distribution of the O(2) class. In addition, minor compound classes could be identified using FTICRMS.

Estimation of bacterial biomass in subsurface sediments by quantifying intact membrane phospholipids.

In an earlier study of deep subsurface sediments from Nankai Trough (ODP Leg 190, offshore Japan) we employed intact phospholipids (PLs) as molecular indicators of living microorganisms. The current study extends this work by quantifying absolute amounts of sedimentary PLs by liquid chromatography-mass spectrometry (LC-MS) and by converting PL data into cell numbers in order to improve methods to estimate the extent of bacterial life in the subsurface. Investigations were carried out on 90 cm short cores of Lake Baikal sediment. High amounts of identified intact PLs are interpreted as reflecting the constituents of living bacteria due to high organic matter decomposition and oxic mineralisation between the epilimnion and the sediment-water interface. Concentrations of ester-bound PLs reach up to 13,120 ng/g sediment dry weight. Predominance of ethanolamine and glycerol PL head groups confirms the bacterial origin. The most abundant side-chain pairs are combinations including 14:0 and 16:0 fatty acids and to a minor extent 15:0 and 16:1 fatty acids. Depth profiles of PL concentrations converted from conventional PL fatty acid analysis are of the same order of magnitude and show comparable trends as those for intact PLs. An approximate estimation of bacterial cell numbers is inferred from intact PL quantification using LC-MS.