Bacterial Methods

In order to measure the propensity for microhial corrosion in a process system it is necessary to quantify both the mobile (planktonic) bacteria and the surface adhering (sessile) bacteria. The mobile bacteria may be enumerated by removing a sample of liquid from the process stream into a clean sterilized container and carrying out a serial dilution test in the lahoratory. 

The tendency for sessile population development within a system should he assessed by using a bioprobe exposed to the process stream through a standard 5.08 cm (2 inch) high-pressure access fitting. Biofihns may also be removed from standard strip coupons protruding into the process stream. 

As bacterial corrosion relies upon the development of hacterial colonies upon the metal surface, it is the determination of sessile populations that is most important in deciding whether or not a problem exists. Bioprobes typically carry six removable studs, on which the hiofihns are allowed to develop. 

Removal of the studs from the bioprobe enables the growth of sessile populations to he quantified and may provide additional information on the morphology of the corrosion to he expected in the system. Typical exposure times for development of biofihns are two to four weeks. 

The corrosion of mild steel as a consequence of the growth of snlfate reducing bacterial populations is characterized by the formation of iron sulfide scale, which can be fairly easily detached to reveal shiny, almost hemispherical continent pits. 

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Dissolved Minerals. The most significant source of minerals for sustainable recovery may be ocean waters which contain nearly all the known elements in some degree of solution. Production of dissolved minerals from seawater is limited to fresh water, magnesium, magnesium compounds (qv), salt, bromine, and heavy water, ie, deuterium oxide. Considerable development of techniques for recovery of copper, gold, and uranium by solution or bacterial methods has been carried out in several countries for appHcation onshore. These methods are expected to be fully transferable to the marine environment (5). The potential for extraction of dissolved materials from naturally enriched sources, such as hydrothermal vents, may be high. 

Sigman et al. [134] have described a bacterial method for measuring the isotopic composition of seawater nitrate at the natural-abundance level. The method is based on the analysis of nitrous oxide gas (N2O) produced quantitatively from nitrate by denitrifying bacteria. The classical denitrification pathway consists of the stepwise reduction of nitrate (NOp to nitrite (N02), nitric oxide (NO), nitrous oxide (N2O), and dinitrogen (N2) ... 

When the bacteria are exposed to the z.-complex, a very interesting picture appears. Not only will they not eat the L-isomer, but it inhibits their growth so obviously this bacterial method cannot be used to resolve the trisethylenediamine complex. There are, of course, thousands of bacteria and hundreds of complexes which we can study. 

Sigman, D. M., Casciotti, K. L., Andreani, M., Barford, C., Galanter, M., and Bohlke, J. K. (2001). A bacterial method for the nitrogen isotopic analysis of nitrate in seawater and freshwater. Analytical Chemistry 73, 4145-4153. 

The growth of autotrophic bacteria on metal sulfides produces acidic solutions of Fe(III). Such solutions can effectively oxidize and solubilize metallic species. The best known example is that of uranium, where insoluble UO2 is oxidized by Fe(III) to give UOi, which dissolves in the acidic solution and subsequently can be recovered chemically. The same result can be achieved using chemically produced Fe(III), but the bacterial method results in the regeneration of the Fe(III) and is economically more attractive. 

The advantage of the bacterial method of purification of starch in com sugar making, over the old bone black method is very marked in several different steps in the process. In the manufacture of com sugar from purified starch no dark bitter modified protein derivatives are produced during the conversion, thus bone black is not necessary for decolorization. Further it is found that a higher purity sugar is produced due to the absence of these modified proteins. 

PBLG prepared via bacterial methods can form smectic liquid crystalline phases, while ordinary polydisperse PBLG exhibits nematic columnar, and cholesteric order in films and in solution. 

HeterometaUic clusters of ferredoxin with the composition [MFe3S4], where M = Zn, Co, Mn, are known. They are present, in particular, in the Pymcoccus furiosus cells. Bacterial methods may be effective in the preparation of finely dispersed precursors of superconducting high-temperature ceramics and other materi-... 

Bacterial methods for sulfur oxidation have also been considered as a means of sulfur removal. 

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