Rb. sphaeroides

The spectroscopy and dynamics of photosynthetic bacterial reaction centers have attracted considerable experimental attention [1-52]. In particular, application of spectroscopic techniques to RCs has revealed the optical features of the molecular systems. For example, the absorption spectra of Rb. Sphaeroides R26 RCs at 77 K and room temperature are shown in Fig. 2 [42]. One can see from Fig. 2 that the absorption spectra present three broad bands in the region of 714—952 nm. These bands have conventionally been assigned to the Qy electronic transitions of the P (870 nm), B (800 nm), and H (870 nm) components of RCs. By considering that the special pair P can be regarded as a dimer of two... 

Figure 2. Absorption spectra of Rb. sphaeroides R26 RC. (Adapted from Ref. 42.)...

The vibrational frequency of the special pair P and the bacteriochlorophyll monomer B have also been extracted from the analysis of the Raman profiles [39,40,42,44,51]. Small s group has extensively performed hole-burning (HB) measurements on mutant and chemically altered RCs of Rb. Sphaeroides [44,45,48-50]. Their results have revealed low-frequency modes that make important contribution to optical features such as the bandwidth of absorption line-shape, as well as to the rate constant of the ET of the RCs. 

Selected Vibrational Frequencies, Huang-Rhys Factors, and Electronic Energy Levels of the Involved States of RCs of Rb. sphaeroides... 

Next we shall discuss how to theoretically construct the three-dimensional fs time-resolved spectra. For this purpose, recent fs time-resolved spectra reported by Scherer s group for Rb. sphaeroides R26 with A,cxcltatlon = 800 nm at room temperature are shown in Fig. 18 is considered [39]. They have used a laser pulse of 30 fs. To theoretically construct the fs time-resolved spectra, we need the potential surfaces for displaced surfaces we need the vibrational frequencies go, and their Huang-Rhys factors S,. For bacterial photosynthetic RCs, these physical constants are given in Table I. In addition to the potential surfaces, we need interactions between different electronic states which are shown in... 

Figure 18. Femtosecond time-resolved spectra for Rb. sphaeroides R26 [39].

Using Table I and Fig. 19, we theoretically construct the fs time-resolved spectra for R26 of Rb. Sphaeroides at room temperature the calculated spectra are... 

Recently, Scherer et al. have used the 10-fs laser pulse with A,excitation = 860 nm to study the dynamical behavior of Rb. Sphaeroides R26 at room temperatures. In this case, due to the use of the 10-fs pulse both P band and B band are coherently excited. Thus the quantum beat behaviors are much more complicated. We have used the data given in Table I and Fig. 19 to simulate the quantum beat behaviors (see also Fig. 22). Without including the electronic coherence, the agreement between experiment and theory can not be accomplished. 

Rb. sphaeroides KD 131 wild type and its mutant strains[17] were obtained from Dr. J. Lee (Sogang University, Korea). 

Figure 1. Growth curves of Rb. sphaeroides KDI31 wild type (A) and mutant strain (B) in the modified Sistrom s broth at 30°C under the 8-9 klux irradiance.

Table 1. Effect of carbon sources on H2 production and cell growth of Rb. sphaeroides KD131 wild-type and mutant strains...

Two photo-bioreactors, A and B, of flat-rectangular shape were compared for the hydrogen production and P-D-HB accumulation in the culture broth during photo-incubation of Rb. sphaeroides KD131 Hup/Phb mutant strain. Both of them had the same dimension, 20... 

Lee at al. [17] recently reported that the cellular PHB accumulated in the wild-type strain of Rb. sphaeroides KCTG 12085 up to 21.9 pg/mg dry weight of cells, while the mutant did not accumulate PHB during photo-incubation. 

Wild type strain of Rb.sphaeroides KD 131 grew well in the Sistrom s broth containing... 

Maximum hydrogen was produced with Hup /Phb mutant and the amount of hydrogen produced was in the increasing order of the wild type strain of Rb. sphaeroides KD131, Phb, Hup, Hup /Phb mutants. 

Rb. sphaeroides RV Saturating light, lactate, glutamate resting cells 180 0.116 235 Nakada et al 1995... 

An approximation based on a general observation of final concentration of Rb. sphaeroides biomass grown in common medium with lactate [Miyake, Kawamura, 1987],... 

Fig. 9. Iron environment in the Rb. sphaeroides photosynthetic reaction center.

Fig. 6.3. Schematic representation of the structure of the reaction center of Rhodobacter (Rb.) sphaeroides.

Fig. 6.4. The absorption spectra of the mutant RC of Rb. sphaeroides R26. Only P and B bands are shown. The absorption spectrum at 77 K (broken line) and that at 298 K are presented.

Fig. 6.6. Numerical simulation of quantum beats measurements of wild-type RCs of Rb. sphaeroides. The box with broken line indicates the time region in which the RCs can keep a clear phase of the vibrational quantum beams.

Scherer s group has reported 10 fsec pump-probe measurements on mutant RCs of Rb. sphaeroides R26 [103]. In this case, at least two electronic states are involved in the pumping process so that the time development of the vibronic coherence should be considered. To perform a numerical simulation on the coupled GMEs (Eqs. (142)-(144)), one has to analyze the absorption spectra of this system first and the energies of the involved electronic states can be determined. The 77 and 298 K absorption spectra... 

Fig. 6.7. Simulated absorption spectra of mutant RCs of Rb. sphaeroides R26. The experimental data are adopted from Refs. [110,121], The calculated higher excitonic band of the special pair is also shown. Reprinted with permission from [110,121]. Copyright (1997, 2001) American Chemical Society.

Fig. 6.8. Calculated pump-probe, delta-absorption profiles for mutant RCs of Rb. sphaeroides R26.

The presented theoretical approach to large molecular systems such as bacterial photosynthetic RCs can provide microscopic details of ultrafast radiationless transition taking place faster than 100 fsec. In particular, this approach establishes a standard model for treating such ultrafast processes of RCs. It is possible to analyze and provide similar details for wild-type RCs or other mutant RCs for example, for wild-type RCs of Rb. sphaeroides the electronic coupling of radiationless transition from the B band to the higher excitonic band and that from the higher excitonic band to the lower one are found to be 105.5 and 123 cm-1. For R26.Phe-a mutant RCs, the former coupling is 105 cm-1 and the latter is 123.7 cm-1. 

G. Hartwich, H. Lossau, A. Ogrodnik, M. E. Michel-Beyerle, Slow Charge Separation in a Minority of Reaction Centers Correlated with a Blueshift of the P860-Band in Rb. sphaeroides, in M. E. Michel-Beyerle (Ed.), The Reaction Center of Photosynthetic Bacteria, Springer-Verlag, Berlin, 1996. 

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