Surface changes in mild steel coupons from the action of corrosion-causing bacteria

Changes which occur on the surface of mild steel coupons submerged in cultures of an Fe(III)-reducing bacterium, isolated from corroded pipe systems carrying crude oil, were studied microscopically to investigate the interaction between the corrosion-causing bacterium and the corroding mild steel coupon. Under micro-aerobic conditions and in the absence of the bacteria, a dense, crystalline, amorphous coat formed on the surface of the steel coupons. In the presence of bacteria the surface coat was extensively removed, exposing the bare metal to the environment. After about 2 weeks of exposure, the removal of the surface coating was followed by colonization of the metal surface by the bacteria. Colonization was mediated by fibrous, exopolysaccharidic material formed by the bacteria. Extension of studies to other bacteria isolated from crude oil and corroded pipes reveals that the formation of exopolysaccharide fibers and possession of adherent properties are common characteristics of bacteria from crude oil systems.

Insight into heterogeneity in cell-surface hydrophobicity and ability to degrade hydrocarbons among cells of two hydrocarbon-degrading bacterial populations

The sequential bacterial adherence to hydrocarbons (BATH) of successive generations of hydrophobic fractions of Paenibacillus sp. R0032A and Burkholderia cepacia gave rise to bacterial populations of increasing cell-surface hydrophobicity. Thus, hydrophobicity of the first generation (H1) was less than that of the second generation (H2), which was less than that of the third generation (H3). Beyond H3, the hydrophobic populations became less stable and tended to lyse in hexadecane after violent (vortex) agitation, resulting in an apparent decline in BATH value. The exhaustively fractionated aqueous-phase population (L) was very hydrophilic. The overall cell-surface distribution of the population was L < parental strain < H1 < H2 < H3. The ability to degrade crude oil, hexadecane, or phenanthrene matched the degree of cell-surface hydrophobicity: L < P < H1 < H2 < H3. Thus, in natural populations of hydrocarbon-degrading Paenibacillus sp. R0032A and B. cepacia, there is a heterogeneity in the hydrophobic surface characteriistics that affects the ability of cells to use various hydrocarbon substrates.

Sequential hydrophobic partitioning of cells ofPseudomonas aeruginosagives rise to variants of increasing cell-surface hydrophobicity

The partitioning of bacterial cells in a dual aqueous-solvent phase system leads to separation into 'hydrophilic' and hydrophobic functions. Sequential multistep partitioning, accompanied by successive enrichment, gives rise to several cycles of hydrophobic and hydrophilic cell populations which possess different cell-surface hydrophobicity characteristics. Characterization of the cell-surface hydrophobicity by several methods (salting-out aggregation test, bacterial adherence to hydrocarbon, polystyrene binding and hydrophobic interaction chromatography) was carried out. The cell-surface hydrophobicity varied in the order: hydrophilic fraction < parental strain < first cycle hydrophobic variant < second cycle hydrophobic variant < third cycle hydrophobic variant. Electron microscopy showed that the most hydrophobic variant was densely covered by hydrophobic structures - fimbriae - whereas the parental strain was covered by a mixture of surface structures. The hydrophilic variant was covered by an amorphous exopolymeric substance, which is a polysaccharide, shown by its reaction with Alcian blue.

High-temperature hydrocarbon biodegradation activities in Kuwaiti desert soil samples

Soil samples taken monthly from the Burgan South oil field of Kuwait for one year degraded crude oil, phenanthrene, and hexadecane. Bacteria were better degraders at high-temperature (55 degrees C) than fungi, especially in the drier, hotter months. Depending on the period of sampling, bacteria degraded hydrocarbons in the range of 46-86% (crude oil), 42-100% (hexadecane) and 5-58% (phenanthrene). Fungi alone accounted for degradation by 20-81% (crude oil), 30-95% (hexadecane) and less than 55% (phenanthrene).

Changes in the disintegration properties of some brands of paracetamol tablets inoculated with four bacterial species

Four most common brands of paracetamol (4-aceta-midophenol) tablets were examined for the changes in their disintegration properties after inoculation with Staphylococcus aureus, Bacillus cereus, Klebsiella aerogenes and Pseudomonas aeruginosa and incubating for 5 weeks. The disintegration times varied from one brand to the other, reaching maximum values of 72 min., 82 min., 110 min. and 120 min. for S. aureus, B. cereus, P. aeruginosa and Klebsiella aerogenes, respectively. All brands of paracetamol tablets revealed the presence of cotton wool-like fibrils which were seen to be interwoven within the tablets' matrices and these were believed to have caused the higher disintegration times.

The relationship between soil copper content and copper resistance in yeast of an ultisol in midwestern Nigeria

Yeast isolates were obtained from the brewer's stock of the Guinness brewery in Benin City, midwestern Nigeria, and from local sources such as mango and sugar cane. The fruits were exposed to the immediate soil environment in eleven selected sites in the Ugbowo and Ikpoba Hill areas of Benin City, Edo State of midwestern Nigeria. A total of twenty-seven yeast isolates were obtained. Fourteen isolates were identified as Saccharomyces cerevisiae and 13 as S. carlsbergensis. Analysis of resistance to copper sulphate revealed that the two brewer's yeast isolates were resistant to 3.5 mM and 4.2 mM CuSO4, respectively, while the local yeasts were resistant to higher concentrations ranging from 6.5 to 16.5 mM. The percentage copper sulphate resistance of yeast isolates obtained from Mangifera inidica ranged from 52.4 to 73.8%, while the percentage copper sulphate resistance of yeast isolates obtained from Saccharum officinarum ranged from 51.8 to 62.6%. The two brewer's yeast isolates (BY2 and BY4) had a percentage CuSO4 resistance of 32.4 and 38.5%, respectively. Comparison of soil copper concentration and copper resistance levels in selected yeast isolates indicated that the soil copper concentrations generally influenced the ability of yeasts to resist copper.

Effects of medium composition on cell pigmentation, cytochrome content, and ferric iron reduction in a Pseudomonas sp. isolated from crude oil

Cells of a pseudomonad associated with pipeline corrosion grown on a complex medium were orange in color and vigorously reduced ferric iron. The intensity of orange color of cells grown on a synthetic medium and their ability to reduce ferric iron was directly related to the iron content of the medium. Absorption spectrophotometric data show a direct relationship between color of cells, cytochrome content, and ability to reduce ferric iron. Carbon monoxide markedly, but not completely, inhibits the reduction of ferric iron. The data presented indicate that ferric iron can serve as a terminal electron acceptor for cytochrome-associated respiratory processes of this corrosive pseudomonad.

Effect of nitrate on reduction of ferric iron by a bacterium isolated from crude oil

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-.