Bacteria chemoautotrophic

FIGURE 8.34 Schematic showing sites of nitrification in wetlands. 

FIGURE 8.35 Pathways and intermediate products of nitrification of ammonium to nitrate. 

FIGURE 8.36 Schematic showing the role of methane oxidizers in nitrification. 

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A sour natural gas stream can be anaerobically desulfurized by a process, which employs a consortium of chemoautotrophic bacteria (ATCC 202177). The H2S and other sulfur species are converted into elemental sulfur, which is recovered as a product [287], The process conditions involve pressures lower than 1000 psi and temperatures up to 60°C. Sulfur content might be diminished from 10,000 ppm H2S to pipeline standards of <4ppm. Further, C02 content can be reduced as well from levels as high as 10% to <2%. 

Oxidation of Fe(ll) occurs rapidly at low pH but at measureable rates of about 1-5 mmol/L/h in surface waters by chemoautotrophic bacteria and archaea (Nordstrom 2003). 

A cytoplasmic hemoglobin of the clam Lucina pectinata has evolved to carry oxygen to symbiotic chemoautotrophic bacteria located within cells of the host s gills. It is also readily oxidized to the Fe3+ methemoglobin form which binds sulfide ions extremely tightly180 182 and is thought to transport sulfide to the bacteria. 

Many organic reactions are slow at low temperatures but are considerably accelerated by temperature increases (I). In addition, living organisms themselves, such as chemoautotrophic bacteria, may accelerate reactions involving dead organic matter. 

The capacity of chemoautotrophic bacteria to oxidize hydrogen sulfide as a source of energy for CO2 fixation is well known (20). However, the realization that entire bacterial and invertebrate communities can be fueled by... 

Jprgensen, B.B. (1989) Biogeochemistry of chemoautotrophic bacteria. In Autotrophic Bacteria (Shlegel, H.G, and Bowien, B., eds.), pp. 117-146, Science Technical Publishers, Madison, Wlp and Springer-Verlag, New York. 

Recently research has revealed that nitrification is not exclusively associated with chemoautotrophic bacteria of the P and y proteobacteria, but occurs in many Crenarcheaota as well (Francis et al, 2005 Konneke et al, 2005 Wuchter et al, 2006) who may in fact may dominate this process in seawater (Wuchter et al, 2006) (see Chapter 5 by Ward, this volume). The extent that archael nitrification occurs in coral reef habitats remains to be determined. Ammonium oxidation has also been shown to occur anoxicaUy in some marine sediments at the expense of N02 (Thamdrup and Dalsgaard, 2002) (see Chapter 6, Devol, this volume). 

Lee RW, Robinson JJ, Cavanaugh CM. Pathways of inorganic nitrogen assimilation in chemoautotrophic bacteria-marine in- 63. vertebrate symbioses expression of host and symbiont glutamine synthetase. J. Exp. Biol. 1999 202 289-300. 

However, much of the methane produced in bottom sediments never reaches the atmosphere because it is oxidized to CO2 by microorganisms living in the surficial layers of the sediments and in the oxic, overlying waters. The oxidation of methane by sulfate reducers (or other organisms in the community) also has been examined and it is the principal removal mechanism of methane from shallow marine sediments (24, 25). Methane is also oxidized by certain chemoautotrophic bacteria in the presence of dissolved oxygen, although at much lower rates compared to those observed in sediments (27). 

Aleem MIH, Lees H, Nicholas DJD (1963) Adenosine triphosphate-dependent reduction of nicotinamide adenine dinucleotide by ferro-cytochrome c in chemoautotrophic bacteria. Nature 200 759-761... 

Some aerobic cocci grown in media containing glutamate are rich in NAD-GDH, which comprises about 10% of the total protein of the organisms (31,32). A distinct NADPH-GDH may also exist in Micrococcus (32) and, in this respect. Micrococcus may be similar to certain facultative chemoautotrophic bacteria (see Table I) which make two separate enzymes with functions similar to those of Neurospora. 

A small part of HjS in the biosphere remains in the form of insoluble sulphides or is spontaneously oxidized with oxygen to elementary sulphur. Photosynthetic and chemoautotrophic bacteria are capable of oxidizing HjS and elementary sulphur to sulphate. This biological oxidation is aflFected either aerobically (colourless sulphur bacteria) or anaerobically (photosynthetic purple and green sulphur bacteria). 

Because of limited oxygen availability in wetland environments, nitrification is restricted to the (1) aerobic water column, (2) aerobic soil-floodwater interface, and (3) aerobic root zone (Figure 8.34). In all these zones, nitrification is supported predominantly by chemoautotrophic bacteria, which use oxygen as their electron acceptor and ammonium as their energy source. Nitrification in these zones is often limited by the availability of ammonium. 

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