Iron oxidizers, bacterial

About a quarter of the total body iron is stored in macrophages and hepatocytes as a reserve, which can be readily mobilized for red blood cell formation (erythropoiesis). This storage iron is mostly in the form of ferritin, like bacterioferritin a 24-subunit protein in the form of a spherical protein shell enclosing a cavity within which up to 4500 atoms of iron can be stored, essentially as the mineral ferrihydrite. Despite the water insolubility of ferrihydrite, it is kept in a solution within the protein shell, such that one can easily prepare mammalian ferritin solutions that contain 1 M ferric iron (i.e. 56 mg/ml). Mammalian ferritins, unlike most bacterial and plant ferritins, have the particularity that they are heteropolymers, made up of two subunit types, H and L. Whereas H-subunits have a ferroxidase activity, catalysing the oxidation of two Fe2+ atoms to Fe3+, L-subunits appear to be involved in the nucleation of the mineral iron core once this has formed an initial critical mass, further iron oxidation and deposition in the biomineral takes place on the surface of the ferrihydrite crystallite itself (see a further discussion in Chapter 19). 

Iron oxide was not mutagenic in bacterial assays with or without metabolic activation. ... 

The oxide surface has structural and functional groups (sites) which interact with gaseous and soluble species and also with the surfaces of other oxides and bacterial cells. The number of available sites per unit mass of oxide depends upon the nature of the oxide and its specific surface area. The specific surface area influences the reactivity of the oxide particularly its dissolution and dehydroxylation behaviour, interaction with sorbents, phase transformations and also, thermodynamic stability. In addition, specific surface area and also porosity are crucial factors for determining the activity of iron oxide catalysts. 

Ferris, F.G. Hallberg, R.O. Lyven, B. Pedersen, K (2000) Retention of strontium, cesium, lead and uranium by bacterial iron oxides from a subterranean environment. Appl. Geochem. 15 1035-1042... 

In addition to a better understanding of the reaction of sulfide with ferric oxides and its role in pyrite formation, a more exact definition of the term reactive iron is critical. Does reactive iron mean a different iron oxide fraction for bacterial dissolution (e.g., weathering products such as goethite or hematite) than for reaction with sulfide (e.g., reoxidized lepidocrocite) In other words, is there a predigestion of ferric oxides by bacteria that allows a subsequent rapid interaction of sulfide with ferric oxides ... 

The observations have shown that consideration must be given to several different processes of carbonate deposition and/or silica or iron oxide deposition in contact which such bacterial mats. Obviously some important lithification processes take place within the decay zone below the active photosynthetic zone. In most of the cases where lithification was observed there, it was carbonate lithification of a type not related to the photosynthetic depletion of C02. Different filamentous and coccoid cyanobacteria can become more or less lithified depending on slime production, mobilization, outer morphology and microenvironments. 

Table 7. Oxidation state of the iron in oxidized bacterial and plant ferredoxin in the presence and absence of p-chloromercuriphenyl sulfonic acid (PCMS)...

Nelson, Y.M. et al., Lead distribution in a simulated aquatic environment Effects of bacterial biofilms and iron oxide, Water Res., 29, 1934, 1995. 

Mineral saturation indices for melanterite and amorphous iron hydroxide agree quite well with field occurrences of the same minerals. Jarosite, however, appears to be supersaturated for nearly all of the samples regardless of the presence or absence of the mineral in these streams. Field observations indicate that jarosite precipitation occurs in the microenvironment of bacterial colonies where the chemical conditions may be quite different from the bulk solution. These considerations lead us to suggest that there is a kinetic barrier which hinders jarosite precipitation but does not hinder ferric hydroxide precipitation and that this barrier is overcome by the surfaces of bacterial colonies (both iron-oxidizers and unidentified nonoxidizers ). ... 

The NH3 can then be further converted into nitrate or nitrite or directly used in the synthesis of amino acids and other essential compounds. This reaction takes place at 0.8 atm N2 pressure and ambient temperatures in Rhizobium bacteria in nodules on the roots of legumes such as peas and beans, as well as in other independent bacteria. In contrast to these mild conditions, industrial synthesis of ammonia requires high temperatures and pressures with iron oxide catalysts, and even then yields only 15% to 20% conversion of the nitrogen to ammonia. Intensive efforts to determine the bacterial mechanism and to improve the efficiency of the industrial process have so far been only moderately successful the goal of approaching enzymatic efficiency on an industrial scale is still only a goal. 

Brock, T.D., 1977. Ferric iron reduction by sulfur- and iron-oxidizing bacteria. Conference Bacterial Leaching. GBF Monograph Series, No. 4 (August 1977), p. 47. 

After iron oxides and manganese oxides have been consumed, bacterial respiration can continue through the use of an even less energetically favorable oxidant, sulfate (SOJ-). The process of sulfate reduction proceeds as follows ... 

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