Joanne Jones-Meehan

Electron energy loss spectroscopy techniques for the study of microbial chromium(VI) reduction

Electron energy loss spectroscopy (EELS) techniques were used to determine oxidation state, at high spatial resolution, of chromium associated with the metal-reducing bacteria, Shewanella oneidensis, in anaerobic cultures containing Cr(VI)O4(2-). These techniques were applied to fixed cells examined in thin section by conventional transmission electron microscopy (TEM) as well as unfixed, hydrated bacteria examined by environmental cell (EC)-TEM. Two distinct populations of bacteria were observed by TEM: bacteria exhibiting low image contrast and bacteria exhibiting high contrast in their cell membrane (or boundary) structure which was often encrusted with high-contrast precipitates. Measurements by EELS demonstrated that cell boundaries became saturated with low concentrations of Cr and the precipitates encrusting bacterial cells contained a reduced form of Cr in oxidation state + 3 or lower.

Oxidation state of chromium associated with cell surfaces of Shewanella oneidensis during chromate reduction

Employing electron energy loss spectroscopy (EELS) and X-ray photoelectron spectroscopy (XPS), we demonstrate that in both aerobic and anaerobic culture Shewanella oneidensis cells are capable of chromate reduction. No Cr(VI) or Cr(V) species were identified at the cell surfaces in Cr 2p3/2 core photoelectron spectra. More chromium was associated with cell surfaces recovered from anaerobic medium than aerobic. Multiplet-splitting models derived for Cr(III) and Cr(IV) were employed to determine contributions from each ion to Cr 2p3/2 photopeaks collected from the various cell treatments. Whilst in all cases Cr(III) was the major ion associated with cell surfaces, a significant contribution was identified due to Cr(IV) in anaerobically grown cells. The Cr(IV) contribution was far less when cells were grown aerobically. Moreover, when anaerobically grown cells were exposed to oxygen very little re-oxidation of Cr-precipitates occurred, the precipitates were again identified as a mixture of Cr(III) and Cr(IV). A positive relationship was observed between amounts of chromium and phosphorous associated with cell surfaces resulting from the various treatments, suggesting the precipitates included Cr(III)-phosphate. The fact that Cr(IV) remained associated with precipitates following re-oxidation suggests that under anaerobic conditions the intermediate ion is afforded sufficient stability to be incorporated within the precipitate matrix and thus conferred a degree of protection from oxidation. # 2002 Published by Elsevier Science B.V.

Spatial relationships between marine bacteria and localized corrosion on polymer coated steel

Diagnosis of microbiologically influenced corrosion on iron‐containing substrata exposed in marine environments cannot be based solely on spatial relationships between large accumulations of bacterial cells and iron corrosion products. Experiments were designed to evaluate the relationship between marine bacteria and localized corrosion on coated mild steel. The distribution of bacteria was strongly influenced by the presence of iron corrosion products independent of coating combinations. In the presence of cathodic protection, coating defects were filled with calcareous deposits and few bacterial cells. The results demonstrate that bacteria are preferentially attracted to iron corrosion products in coating defects and that attraction is more influential than topography in determining the spatial distribution of bacterial cells.

An evaluation of microbial growth and corrosion of 316L SS in glycol/seawater mixtures

Glycol/seawater mixtures containing >50% glycol inhibit corrosion of 316L stainless steel and do not support bacterial growth. The results indicate bacteria are able to use low concentrations of glycol (10%) as a growth medium, but bacterial growth decreased with increasing glycol concentration. Pitting potential, determined by anodic polarization, was used to evaluate susceptibility of 316L SS to corrosion in seawater-contaminated glycol. Mixture containing a minimum concentration of 50% propylene glycol-based coolant inhibited pitting corrosion. A slightly higher minimum concentration (55%) was needed for corrosion protection in ethylene glycol mixtures.

Sulfur isotope fractionation by sulfate‐reducing bacteria in corrosion products

Sulfur isotope fractionation was demonstrated in preliminary studies of corrosion products resulting from the activities of sulfate‐reducing bacteria within biofilms on copper surfaces. 32S accumulated in corrosion products, 34S was concentrated in the culture medium. The accumulation of the lighter isotope was related to surface derivatization or corrosion as measured by weight loss.