Metal depositing bacteria

Metal depositors. Metal-depositing bacteria oxidize ferrous iron (Fe ) to ferric iron (Fe ). Ferric hydroxide is the result. Some bacteria oxidize manganese and other metals. Gallionella bacteria, in particular, have been associated with the accumulation of iron oxides in tubercles. In fact, up to 90% of the dry weight of the cell mass can be iron hydroxide. These bacteria appear filamentous. The oxide accumulates along very fine tails or excretion stalks generated by these organisms. 

Bacteria which oxidize ferrous iron (Fe2+) to ferric iron (Fe3+) such as Gallionella and Leptothrix species are termed metal-depositing bacteria. The result of this metabolic process is the formation of ferric hydroxide. 

Cowen, J. P. Fe and Mn depositing bacteria in marine suspended macroparticulates, in Biomineralization and biological metal accumulation (eds. Westbroek, P., de Jong, E. W.) p. 489, Dordrecht, Boston, London, D. Reidel P.C. 1983... 

Cowen, J.P. and Bruland, K.W., 1985. Metal deposits associated with bacteria implications for Fe and Mn marine geochemistry. Deep-Sea Research, 32A 253-272. 

Acid producers. Corrosion usually is moderate and localized. Almost all significant attack is associated with anaerobic bacteria (facultative and obhgate), as aerobic acid-producing varieties usually reside near the top of deposits and corrosion products contacting oxygenated waters. Thus, the direct effect on corrosion at metal surfaces is limited. Additionally, although acidic products may be expected to increase corrosion rates, acidity cannot be pronounced in deposits to put it simply, the deposits and corrosion products would dissolve at sufficiently acidic pH. 

Scale deposits create conditions for concentration-cell corrosion as they do not form uniformly over the metal surface. Sulfate-reducing bacteria thrive under these deposits, producing hydrogen sulfide and, consequently, increasing the rate of corrosion. Due to the following factors, the drilling fluid environment is ideal for scale deposition [189]. These factors are as follows ... 

The carbon dioxide produced can contribute to the corrosion of metal. The deposits of ferric hydroxide that precipitate on the metal surface may produce oxygen concentration cells, causing corrosion under the deposits. Gallionalla and Crenothrix are two examples of iron-oxidizing bacteria. 

Fig. 15.26 The effect of applying positive (A) and negative (B) potential to the metal layer of the MCLW sensor on deposition and repulsion of different concentrations of BG bacteria spores. Reprinted from Ref. 22 with permission. 2008 The Royal Society of Chemistry...

Snbmerged soils are important sinks for atmospheric snlfnr (Howarth et al 1992). Snlfate washed into wetlands or deposited from the atmosphere is largely rednced to snlflde by sulfate-reducing bacteria. Subseqnent precipitation with metals, especially as FeS, results in more or less permanent removal of the S from the global S cycle. 

The first important commercial builder was sodium tripol3q)hosphate, NasPsOio, first used with Tide detergent in 1947. Besides sequestering polyvalent metal ions, it prevents redeposition of dirt, buffers the solution to pH = 9 -10, kills bacteria, and controls corrosion and deposits in the lines of automatic washers. 

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