Aerobic bacteria, microbial

In some undisturbed subsurface systems, an equilibrium is established. Bacteria have acclimated to food sources, water availability, and electron acceptor types. The number and variety of microbial cells are balanced in this system. If the system is aerobic, the microbial activity continues at the rate of oxygen resupply. If the system is anaerobic, the rate of activity cannot exceed the accessibility of alternate electron acceptors. Generally, the subsurface (lower than the plant root zone) is relatively deficient in available carbon and electron acceptors. Under these normal semi-equilibrium conditions, a soil or aquifer system can consume organic materials within a reasonable range. When a chemical release is introduced into a well-established soil system, the system must change to react to this new energy source. The bacterial balance readjusts, in an effort to acclimate to the new carbon source. 

If DMS concentrations at the surface of the ocean are presumed to be at steady state, production must balance loss. The fate of DMS is thought to be evasion across the sea surface into the marine atmospheric boundary layer. However, since rates of DMS production are unknown, it is impossible to compare production with flux to the atmosphere, which is relatively well constrained. An alternative sink for DMS in seawater is microbial consumption. The ability of bacteria to metabolize DMS in anaerobic environments is well documented (32-341. Data for aerobic metabolism of DMS are fewer (there are at present none for marine bacteria), but Sivela and Sundman (25) and de Bont et al. (25) have described non-marine aerobic bacteria which utilize DMS as their sole source of carbon. It is likely that bacterial turnover of DMS plays a major role in the DMS cycle in seawater. 

Other microbially mediated processes can control the release of P from sediments. For example, in fresh to brackish waters Fe-reducing aerobic bacteria convert amorphous Fe(III) into Fe(II)-releasing Fe-associated PO/j3-. 

Attack by organisms other than SRB. Ammonia and amines are produced by microbial decomposition of organic matter under both aerobic and anaerobic conditions (ammo-nification). (Stott)5 These compounds are oxidized to nitrite by aerobic bacteria such as Nitrosomonas or Nitrobacter species. Nitrobacter is very efficient at destroying the corrosion-inhibition properties, of nitrate-based corrosion inhibitors by oxidation, unless a biocidal agent is included in the formulation. The release of ammonia at the surfaces of heat-exchanger tubes has a detrimental effect. (Stott)5... 

Usually, total aerobic bacteria, molds, and yeasts are counted by using a standard plate count in order to test the microbial limits. The microbial limit test may be customized by performing a screening for the occurrence of Staphylococcus aureus, Pseudomonas aeruginosa, Pseudomonas cepacia, Escherichia coli, and Salmonella sp. [56],... 

Another solid-phase treatment involves the same approach to enhancing microbial activity but relies on a different way of providing O2. Here, additional air is provided by vacuum extraction of soil above the water table (i.e., the vadose zone or the unsaturated soil layer), thereby supplying the terminal electron acceptor needed by the aerobic bacteria. This process, designed for hydrocarbon-contaminated sites, is termed bioventing or simply venting. 

Although they are known to be synthesized by a wide variety of cultured aerobic bacteria there does not appear to be any obligate requirement for oxygen in their biosynthesis. The biosynthesis and cyclization of squalene to a pentacyclic triterpenoid with a hopane skeleton does not seem to require oxygen and, therefore, hopanoid synthesis might also be possible in anaerobes. For instance, analysis of microbial mats at methane seeps under anoxic Black Sea water revealed the presence of C-depleted (8 C = -lS%c) hopanoids with an unusual stereochemistry. This isotopic depletion indicates in situ production and, therefore, suggests that anaerobes are responsible (Thiel et ai, 2003). 

It was recently described that such a two-step process was also occurring in the course of the microbial oxidation of the olefinic precursor of fosfomycin, a clinically important, broad spectrum antibiotic. Fifteen strains of aerobic bacteria as well as two fungal strains were shown to produce optically active fosfomycin [79]. 

Microbial limits Total viable count for aerobic bacteria and yeasts/molds. X X... 

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