Bacteria reducing

A third resistance mechanism is akin to that described for the AGAC antibiotics and chloramphenicol, whereby changes in the outer membrane porins of Gram-negative bacteria reduce the penetration of /3-lactams resulting in low levels of resistance. 

A biosensor for nitrite [24] was recently proposed for monitoring nitrite concentration in activated sludge exposed to oxic/anoxic cycles. The biosensor contains bacteria reducing only N02 into N20, which is subsequently monitored by a built-in electrochemical sensor. Up to 90% of the response is obtained in about 1 min, and the detection limit is around 5 mg L1, a concentration sufficient for treatment process monitoring. Unfortunately, the maximum operational lifetime of the N02 biosensor is 6 weeks and some problems may occur with time. 

Where oxygen is readily available and all of the necessary components are present, existing bacteria reduce oxygen by the addition of protons (H+ ions) to form water, carbon dioxide, and energy. Aerobic reactions are relatively rapid, often in terms of hours. The following general equation describes this activity ... 

Sulfate-reducing bacteria reduce sulfate to HjS, Methanogens reducing COj to methane... 

Not all cytochromes from sulfate-reducing bacteria reduce Fe(III) or other metals. D. vulgaris produces a cyt C553, which has a molecular mass of 9 kDa, midpoint redox potential of OmV, and a single heme and the iron atom is coordinated by histidine methionine. It is unclear at this time if the inability of this cyt C553 to reduce metals is due to lack of a bishistidinyl iron coordination or to some other factor, such as steric hinderance owing to orientation of heme in the protein. 

It is important to identify and measure the concentrations of a number of compounds in a mixture simultaneously for several reasons. First, among related compounds there may exist precursors of active ones, and pathways of pheromone synthesis may be elucidated. This is true for steroids in the human axilla. Nixon etal. (1988) determined the concentration of five steroids extracted from axillary hair of adult men aged 18 to 40 years. The relationships in concentrations between the two ketones 5Q -androst-16-en-3-one and 4,16-androstadien-3-one suggest that axillary bacteria reduce the former to the latter with the aid of the enzyme 4-ene-5a-reductase. Humans have a low olfactory threshold for several 16-androstenes, and the fact that some men have large quantities of 16-androstenes (Nixon etal., 1988) is biologically suggestive. 

Cytochrome c nitrite reductase (bacteria) Reduces HA and NH2OCH3 to ammonia (NH3) 10, 23... 

Like estuary and marine sediments, arsenic may also migrate into deeper sediments where bacteria reduce sulfate to sulfide (Figure 3.4). In such highly reducing environments, arsenic might be incorporated into relatively stable sulfide minerals (Ford, Wilkin and Hernandez, 2006). 

Apart from hydrogen evolution, the electrons of reduced ferredoxin can take alternative routes leading to biosynthesis. In anaerobic bacteria, reduced ferredoxin can be used directly for the reduction of pyridine nucleotides (Tagawa and Arnon (99) Valentine, Brill and Wolfe (107) Fredericks and Stadtman (44)) for the reduction of hydroxyla-mine to ammonia (Valentine, Mortenson, Mower, Jackson, and Wolfe (109) for COa fixation in the reductive carboxylation of acetyl-CoA to pyruvate (Bachofen, Buchanan, and Arnon (13) Raeburn and Rabino-witz (83) Andrews and Morris (3) Stern (98)) for the reduction of sulfite to sulfide (Akagi (1)) and, in the presence of ATP, it can be used for the reduction of N2 to NH3 (Mortenson (72,73) D Eustachio and Hardy (40)). The role of ferredoxin in these reactions as well as in the oxidative degradative reactions discussed above is summarized in Fig. 10. 

Mechanism of action Sensitive bacteria reduce the drug to an active agent that inhibits various enzymes and damages DNA. Activity is greater in acidic urine. 

Those photosynthetic eubacteria with RC-2 centers (filamentous and purple bacteria) reduce NAD" for CO2 fixation by reverse electron flow from the quinone pool, whereas the green sulfur bacteria (RC-1 center) reduce ferredoxin and NAD directly from the secondary acceptor (Fe-S center) of the RC. In both cases an external reductant such as H2S is required. The mechanism of NAD reduction in the gram-positive line has not yet been investigated, but H. chlorum is a het-erotroph rather than an autotroph, and may not need to fix CO2. 

K Green vegetables and synthesized by intestinal bacteria Reduced blood clotting abiUty None known... 

Leptothrix ochracea, whereas chemohthoautotrophic iron bacteria reduce CO rather than oxidize ambient organic material by means of Fe(III), yet assuming the same C/N ratio... 

Enzymes from indigenous bacteria reduce trimethyl-amine oxide to trimethyl-amine (NADH dependant) coupled with the oxidation of lactic acid to acetic acid and CO2. 

Nitrate intoxication has been described in a patient receiving hemodialysis at home. Using well water contaminated with nitrates, the patient developed dyspnea, sweating, and cyanosis. The venous blood acquired a brownish color and the arterial p02 decreased and failed to rise with the administration of 02. His condition reversed with the intravenous administration of methylene blue. Nitrate must be converted to nitrite before it can convert hemoglobin (ferrous) to methe-moglobin (ferric). The authors of this case report postulated that nitrate must have diffused from the blood into the gut, where the resident bacteria reduced it to nitrite, which then diffused back into the blood (C3). 

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