Photosynthetic bacteria oxidation

Hydrogen Photosynthetic bacteria, methane oxidation A few years... 

As can be seen in these reactions, carotenoids may protect photosynthetic bacteria at various levels by quenching the singlet-excited state of O2 or the tiiplet-excited state of chlorophyll. The ground states of oxygen would be 3O2 and for CHL the triplet state. The carotenoids may be the preferred substrates for oxidation or may act in quenching reactive species. ... 

Modem layered microbial communities provide a view into biochemical redox cycling. Oxidation of Fe(ll) through high O2 contents generated by cyanobacteria generally occurs in the top most (photic) portions of microbial mats. The upper, near-surface layers of microbial mats that are rich in cyanobacteria are commonly underlain by purple and green anoxygenic photosynthetic bacteria that thrive in the IR photic spectra (Stahl et al. 1985 Nicholson... 

The biological classification schemes for bacteria and archaea are still being developed because of the rapid pace of new discoveries in genomics. The two most important phyla of marine bacteria are the cyanobacteria, which are photosynthetic, and the proteobacteria. The latter include some photosynthetic species, such as the purple photosynthetic bacteria and N2 fixers. Other members of this diverse phylum are the methanotrophs, nitrifiers, hydrogen, sulfur and iron oxidizers, sulfete and sulfur reducers, and various bioluminescent species. 

Bacterial ferredoxins function primarily as electron carriers in ferredoxin-mediated oxidation reduction reactions. Some examples are reduction of NAD, NADP, FMN, FAD, sulfite and protons in anaerobic bacteria, CO -fixation cycles in photosynthetic bacteria, nitrogen fixation in anaerobic nitrogen fixing bacteria, and reductive carboxylation of substrates in fermentative bacteria. The roles of bacterial ferredoxins in these reactions have been summarized by Orme-Johnson (2), Buchanan and Arnon (3), and Mortenson and Nakos (31). 

Rieke proteins, 47 337, 347-355 superoxide dismutases and, 45 129 Photosynthetic bacteria, 2[4Fe-4S] and [4Fe-4S] [3Fe-4S] ferredoxins, 38 255-257 Photosystem 1, 38 303-304 Pa/Fb proteins, 38 262-263 reaction center X proteins, single [4Fe-4S] ferredoxins cluster bridging two subunits, 38 251-252 Photosystem II, 46 328 interatomic separations, 33 228 mechanisms for water oxidation, 33 244-247... 

These bacteria, instead of producing molecular 02, form elemental sulfur as the oxidation product of H2S. (They further oxidize the S to SOf A) Other photosynthetic bacteria use organic compounds such as lactate as electron donors ... 

If an enzyme binds a flavin radical much more tightly than the fully oxidized or reduced forms, reduction of the flavoprotein will take place in two one-electron steps. In such proteins the values of E° for the two steps may be widely separated. The best known examples are the small, low-potential electron-carrying proteins known as flavodoxins.266 269a These proteins, which carry electrons between pairs of other redox proteins, have a variety of functions in anaerobic and photosynthetic bacteria, cyanobacteria, and green algae. Their functions are similar to those of the ferredoxins, iron-sulfur proteins that are considered in Chapter 16. 

Measured rates of microbial oxidation of sulfide in lakes range from 0 to over 100,000 mmol/m2 per year (Table IV). These rates, which are comparable to measured rates of sulfate reduction (Table I), suggest that microbial oxidation of sulfide is capable of supplying sulfate at rates needed to sustain sulfate reduction. The majority of measurements are for photosynthetic bacteria in the water column. Symbiotic sulfate reduction and sulfide oxidation are known to occur and lead to dynamic cycling of S within anaerobic water... 

The sulfide produced by sulfate reducers may be oxidized by several sulfur bacteria. Common among these are members of Beggiotoales and Thiobacteriaceae, as well as photosynthetic bacteria of Thiorhodaceae and Chlorobacteriaceae, which are common in eutrophic lakes in which the hypolimnion is depleted in oxygen. An example is the development... 

The traces shown here are measurements of optical absorbance changes at 870 and 550 nm when a suspension of membrane vesicles from photosynthetic bacteria was excited with a short flash of light. Downward deflection of the traces represent absorbance decreases. Explain the observations. (Absorption spectra of a c-type cytochrome in its reduced and oxidized forms are described in the previous chapter.)... 

These are involved in a wide range of electron-transfer processes and in certain oxidation-reduction enzymes, whose function is central to such important processes as the nitrogen cycle, photosynthesis, electron transfer in mitochondria and carbon dioxide fixation. The iron-sulfur proteins display a wide range of redox potentials, from +350 mV in photosynthetic bacteria to —600 mV in chloroplasts. 

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