No abstract

Gram-negative, aerobic bacteria capable of facultative growth using ferric ions or thiosulfate or sulfite as electron acceptors were readily isolated from oil field fluids. Morphological and biochemical data are presented which support the classification of these isolates as being strains of Alteromonas putrefaciens (mol% G + C in the range 42–56%). The isolates expressed a range of halotolerance and temperature tolerance as some would grow in the presence of 7.5% NaCl and some grew well at 4 °C. These physiological characteristics, together with the ability to produce ferrous ions and sulfide and their ubiquitous presence in oil field fluids, indicate that these bacteria could contribute to the corrosion of metal in the oil field environment.

A Pseudomonas sp. isolated from crude oil reduced ferric ions (Fe(III)) to ferrous ions (Fe(II)). In the presence of nitrate (NO3-) after prolonged incubation, the amount of Fe(II) was lower than in its absence. However, during short incubation periods, the presence of NO3- significantly increased (99.5% confidence limit) the amount of Fe(II) produced. The decrease in Fe(II) on prolonged incubation was associated with increased production and accumulation of nitrite (NO2-). Under low NO3- levels, where the production of NO2- was limited, a decrease in NO2- concentration was accompanied by an increase in Fe(II) production to levels comparable with those obtained in the absence of NO3-. Preinduction of cells for nitrate reductase, which favoured rapid NO2- production, resulted in a more rapid decrease in Fe(II) production than in cells that were not preinduced. It is proposed that the inhibitory effect of NO3- on microbial reduction of Fe(III) is due to a secondary reaction, which involves the chemical oxidation of Fe(II) by NO2-.

Enrichment cultures were established with the aromatic fraction of a crude oil and screened for aromatic-degrading pseudomonads, using a sprayed plate technique. One isolate identified as Pseudomonas sp. HL7b was chosen for further study because it oxidized several polycyclic aromatic hydrocarbons and aromatic heterocycles without an apparent lag. Using capillary gas chromatography, spectrophotometry, and radiorespirometry, it was found to be capable of mineralizing and (or) oxidizing a wide range of polycyclic aromatic hydrocarbons, S-, N-, and O-heterocyclic analogues, and alkyl polycyclic aromatic hydrocarbons, but not aliphatic hydrocarbons. The isolate displayed two colonial morphologies which correlated with variation in degradative phenotype and hydrophobicity as measured by polystyrene adherence. Four cryptic plasmids were observed in both colonial types. Pseudomonas sp. HL7b degraded dibenzothiophene co-metabolically by a recognized pathway, but this degradation was constitutive, rather than inducible as reported for other bacteria.

Four crude oils (Prudhoe Bay, Norman Wells, Atkinson Point, and Lost Horse Hill) of different chemical composition were tested as to their biodegradability under mesophilic and psychrophilic conditions. Changes in bacterial numbers and chemical composition of the oils were monitored using a plate count and chromatographic technique respectively. Populations induced under psychrophilic conditions readily metabolized similar quality oils under mesophilic conditions. Mesophilic populations, however, only showed a limited metabolic capability on similar quality oils under psychrophilic conditions. Gram-negative rods were predominant in all the populations obtained under these experimental conditions. The ability of the mixed populations to use crude oil as a sole carbon source was dependent not only on the composition and amount of the n-saturate fraction but also on that of the asphaltene and NSO (i.e. nitrogen-, sulfur-, and oxygen-containing) fraction. Growth on an oil which lacked a normal n-alkane component indicated that the aromatic fraction of oil was capable of sustaining bacterial growth. Oil quality and temperature of incubation affected the generic composition of populations obtained which would use crude oil. The isoprenoids, phytane and pristane, while readily used under mesophilic conditions, were more resistant to bacterial metabolism under psychrophilic conditions.