Green filamentous bacteria

Another nonheme Mn center is believed [172] to be present in photosynthetic green filamentous bacteria. The locus of the Mn ion in these bacteria is similar to that of the nonheme Fe11 in photosynthetic purple bacteria [173], i.e., between two quinones, along the pathway of electron transfer. Since the Fe center of purple bacteria does not seem to be involved directly in the electron transfer process (i.e., is not redox-active), the redox role of the Mn analog remains in question. This Mn may be redox-active, considering that (1) structural differences between the purple and green bacteria photosynthetic apparatus do exist [173] and (2) the green bacteria display different functionalities, such as C02 fixation, which does not occur via the classical Calvin or reverse Krebs cycle [174],... 

Interestingly, reaction centers of apparently all photosynthetic organisms may be assigned to one or the other of these two types. For instance, the reaction center of both purple bacteria and the green filamentous bacteria, Chloroflexaceae, and green-plant PS II are of the OQ-type. On the other hand, the green sulfur bacteria, Chlorobiaceae, the Heliobacteria, and photosystem I all have the FeS-type reaction centers. 

A. Preparation and Properties of Reaction-Center Complexes of Green Filamentous Bacteria...168... 

C. Secondary Electron Acceptor in Green Filamentous Bacteria Menaquinone. 170... 

Pigment and cofactor compositions as well as the light-induced absorbance changes in the reaction centers of green filamentous bacteria are similar to those of purple bacteria. Fig. 8 (A) shows room-temperature absorption spectra for the reaction center of Cf aurantiacus reduced by Asc (solid line) in one case and in the other oxidized by FeCy (dashed line). The far-red absorption maxima of the reduced sample are at 865, 815 and 756 nm while in the oxidized sample, most ofthe 865-nm band and some of the 605-nm band are bleached and the 815- and 756-nm bands are shifted to 806 and 757 nm, respectively. A distinct shoulder at 793 nm also disappears upon oxidation. The BO-a absorption band at 534... 

The RC of green filamentous bacteria contain a membrane-bound cytochrome c554, which with a redox potential is -hO.26 V can reduce P865 in 10 /js at room temperature. When electron transfer is interrupted either on the donor or the acceptor side, P865 and 1 recombine to form the spin-polarized triplet state through the radical-pair mechanism. The decay time of P865 at room temperature is 90 ps. 

II.D. Picosecond Spectroscopic Measurement of the Intermediate Electron Acceptor (I) in Green Filamentous Bacteria... 

As in the case of the purple photosynthetic bacteria, the more stable electron acceptor of green filamentous bacteria was first detected using instrumentation with millisecond-time resolution and so the rise and decay kinetics of any earlier electron acceptor(s) would be too fast to be detected. The detection of any earlier electron acceptor would require greater time resolution, such as afforded by picosecond spectroscopy. As a framework for further discussion we write the sequence of the primary photochemical and electron-transfer reactions in green filamentous bacteria as follows ... 

Green sulfur bacteria Green filamentous bacteria... 

Fig. 11. Electron-transfer schemes for the reaction centers of the green sulfur bacteria (A) and green filamentous bacteria (B). The reaction-center components of the green sulfur bacteria are compared to green-plant photosystem I and those of the green filamentous bacteria are compared to green-plant photosystem II or purple bacteria. The decay times and redox potentials are for Prosihecochloris aestuariiand Chloroflexus aurantiacus. See text lor discussion. Figure adapted from Amesz (1987)...

The Chloroflexaceae are green filamentous bacteria. They form a deep division in the eubacterial line and have an interesting combination of the characteristics found in very different and diverse groups of photosynthetic bacteria (Pierson and Castenholz,... 

The green filamentous bacteria were discovered in the early seventies (2). Only one species has been extensively studied so far, Chloroflexus aurantiacus, a thermophilic bacterium living in hot springs in various parts of the world. The main pigment of Cfl. aurantiacus is BChl c, contained in chlorosomes, whereas the cytoplasmic membrane contains BChl a. Chloroflexus can grow phototrophically as well as heterotrophically in the presence of oxygen. 

The absorption spectra of green sulfur as well as of green filamentous bacteria are dominated by strong absorption bands near 460 and 720-760 nm. These bands belong to BChl c, d ox e in the chlorosomes, the major antenna systems in these bacteria. In addition to BChl c chlorosomes of green sulfur bacteria (5-7) as well as those of Cfl. aurantiacus (5,8) contain small amounts... 

In contrast, eubacteria (including purple bacteria, green filamentous bacteria, and heliobacteria), archaea, and fungi use only one enzyme phytoene desaturase (CrtI) to convert phytoene 3 to lycopene 7. Exceptionally, the primitive cyanobacterium Gloeobacter violaceus PCC 7421 uses this CrtI [29, 30]. G. violaceus is the first oxygenic phototroph that has been shown to use this enzyme (Table 106.3), whereas green sulfur bacteria use CrtP, CrtQ, and CrtH [14, 31]. 

Green filamentous bacteria, 3257, 3258 Greenhouse, 330, 331 Green leaf volatiles (GLVs), 2934 Green pepper, 311... 

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