Green sulfur bacteria

Anoxygenic photosynthetic bacteria. Green sulfur bacteria. Chlorobium, Prosthecochloris purple nonsulfur bacteria Rhodopseudomonas, Rhodospirillum purple sulfur bacteria Chromatium, Thiospirillum... 

A-9 Photoautotrophs - Photoautotrophs use light as an energy source and carbon dioxide as their main carbon source. They include photosynthetic bacteria (green sulfur bacteria, purple sulfur bacteria, and cyanobacteria), algae, and green plants. 

Bacteriochloro- phyll Bacterioviridin Purple sulfur bacteria Green sulfur bacteria Infra-red, blue-violet Red and blue-violet Exists in several forms... 

Purple sulfur bacteria Green sulfur bacteria Sulfate-reducing bacteria... 

Each of the two photosystems found in plants is found in a different color of bacteria. Green sulfur bacteria have photosystem 1, but purple bacteria have photosystem II. The two photosystems are chemically distinct, even using different elements. 

Bacteriochlorophyll- Light-absorbing pigment found in green sulfur and purple sulfur bacteria. 

Flowever, many photosynthetic bacteria, such as purple sulfur and green sulfur bacteria contain special bacteriochlorophyll compounds (not chlorophyll a) and carry out anoxygenic photosynthesis without producing oxygen ... 

Purple sulfur bacteria fix carbon dioxide using the Calvin-Benson cycle, but green sulfur bacteria use a completely different pathway, the reverse tricarboxylic acid cycle. Other photosynthetic bacteria use still different pathways for CO2 fixation (Perry and Staley, 1997). 

Fig. 3. Sequence comparison of the FA/FB-binding subunits of PSl from tobacco and the RC of green sulfur bacteria with that of the 2[4Fe-4S] ferredoxin from Peptococcus aerogenes. Cysteine ligands to the right-hand cluster in the three structures of Fig. 2 (i.e., cluster Fb for the case of the FA/FB-protein) are marked by open boxes Emd residues ligating the left-hand cluster by hatched boxes.

Cluster Fx was also identified via its EPR spectral features in the RCI photosystem from green sulfur bacteria 31, 32) and the cluster binding motif was subsequently found in the gene sequence 34 ) of the (single) subunit of the homodimeric reaction center core (for a review, see 54, 55)). Whereas the same sequence motif is present in the RCI from heliobacteria (50), no EPR evidence for the presence of an iron-sulfur cluster related to Fx has been obtained. There are, however, indications from time-resolved optical spectroscopy for the involvement of an Fx-type center in electron transfer through the heliobacterial RC 56). 

Fig. 6. Sequence comparisons of Rieske proteins from spinach chloroplasts, beef heart mitochondria, green sulfur bacteria, and firmicutes. The extended insertion of proteobacterial Rieske proteins as compared to the mitochondrial one is indicated by a dotted arrow. The redox-potential-influencing Ser residue is marked by a vertical arrow. The top and the bottom sequence numberings refer to the spinach and bovine proteins, respectively. Fully conserved residues are marked by dark shading, whereas the residues conserved in the b6f-group are denoted by lighter shading.

Bacteriochlorophyll c 428, 660 Green sulfur bacteria Green -C2CH3-0H -CH3 -CH2CH3 -CH CH COO-farnesyl Single Single... 

Nonomnra, Y. et al.. Spectroscopic properties of chlorophylls and their derivatives inflnence of molecnlar stmctnre on the electronic state, Chem. Phys., 220, 155, 1997. Blairkenship, R.E., Identification of key step in the biosynthetic pathway of hacteri-ochlorophyU c and its implications for other known and nirknown green sulfur bacteria, J. Bacterial., 186, 5187, 2004. 

Fig. 5.7. In green sulfur bacteria and in some archaebacteria, a reverse citric acid cycle is used for the assimilation of C02. It must be assumed that this was the original function of the citric acid cycle that only secondarily took over the role as a dissimulatory and oxidative process for the degradation of organic matter. A major enzyme here is 2-oxoglutarate ferredoxin for C02 fixation. Note that it, like several other enzymes in the cycle, uses Fe/S proteins. One is the initial so-called complex I which has eight different Fe/S centres of different kinds but no haem (see also other early electron-transfer chains, e.g. in hydrogenases).

In the BChl g containing heliobacteria Heliobacillus mobilis and Heliobacterium chlorum symmetric dimers for the primary donor radical cation PgJ5 have been found based on EPR and ENDOR data.85 This symmetric dimer is consistent with the homodimeric structure of the RC. The same reason was invoked to explain the high symmetry of the donor radical-cation Pgg5 in green sulfur bacteria, which is made up from a BChl a dimer.86 For a review see reference 87. Note that these RCs belong to the type I RCs. 

Photosynthetic bacteria have relatively simple phototransduction machinery, with one of two general types of reaction center. One type (found in purple bacteria) passes electrons through pheophytin (chlorophyll lacking the central Mg2+ ion) to a quinone. The other (in green sulfur bacteria) passes electrons through a quinone to an iron-sulfur center. Cyanobacteria and plants have two photosystems (PSI, PSII), one of each type, acting in tandem. Biochemical and biophysical... 

The Fe-S Reaction Center (Type I Reaction Center) Photosynthesis in green sulfur bacteria involves the same three modules as in purple bacteria, but the process differs in several respects and involves additional enzymatic reactions (Fig. 19-47b). Excitation causes an electron to move from the reaction center to the cytochrome bei complex via a quinone carrier. Electron transfer through this complex powers proton transport and creates the proton-motive force used for ATP synthesis, just as in purple bacteria and in mitochondria. 

However, in contrast to the cyclic flow of electrons in purple bacteria, some electrons flow from the reaction center to an iron-sulfur protein, ferredoxin, which then passes electrons via ferredoxin NAD reductase to NAD+, producing NADH. The electrons taken from the reaction center to reduce NAD+ are replaced by the oxidation of H2S to elemental S, then to SOf, in the reaction that defines the green sulfur bacteria. This oxidation of H2S by bacteria is chemically analogous to the oxidation of H20 by oxygenic plants. 

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