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Under photosynthetic growth, purple non–sulfur photosynthetic bacterium Rhodobacter sphaeroides can use a diverse array of substrates for the source of carbon donor. Substrates such as acetate and succinate are most commonly used to study energetic and metabolic networks, especially in the production and consummation of NADPH during the citric acid cycle (TCA cycle) and ethylmalonyl–CoA pathway, respectively. Although the utilization of both substrate, the bacterium will grow at different growth rate and this also influence the biosynthesis of photosynthetic pigments as important components for overall photosynthesis. For this study, Rhodobacter sphaeroides strain 2.4.1, GA and G1C have been grown in acetate and succinate. Here, preliminary results on the evaluation the pigment ratio at different stages of the growth is reported, especially on the growth in succinate substrate. [ABSTRACT FROM AUTHOR]

Photosynthetic purple bacteria have developed sophisticated processes to adapt their photosynthetic unit towards changes in light illumination in which the cells grow. Some purple bacteria show pronounced modification of their PSU from changing the composition and content of photosynthetic pigments, i.e. carotenoids, to replacing different composition of polypeptides that alter the Q y absorption bands of bacteriochlorophyll. Adjusting the spectrum by shifting spectral band position or tuning absorption intensity of spectral band are keys to collect light energy at specific ecological niches they inhabit. Furthermore photoprotection system will ensure the complex from damage. [ABSTRACT FROM AUTHOR]

Abstract: Five strains (JA325, JA389, JA473, JA563 and JA582) of Gram stain-negative, vibrioid to spiral shaped, phototrophic purple bacteria were isolated from solar salterns of India. All strains contained bacteriochlorophyll-a and carotenoids of the spirilloxanthin series as photosynthetic pigments. C18:1ω7c, C18:1ω7c 11-methyl and C16:0 were the major fatty acids of all strains. Diphosphatidylglycerol (DPG), phosphatidylglycerol (PG), ornithine lipid (OL), an unidentified phospholipid (PL), and an unidentified aminolipid (AL) were the major polar lipids of all the strains. According to 16S rRNA gene sequences, all strains clustered phylogenetically with the only species of the genus Rhodothalassium (99.8–99.3% sequence similarity) but only strains JA325 and JA563 were distinctly related (60+1.5% DNA–DNA hybridization [DDH]) to the type strain Rhodothalassium salexigens DSM 2132T. However, the genotypic data of strains JA325 and JA563 was not supported because of a large number of phenotypic differences compared to the type strain, therefore, it is proposed that all five newly isolated strains were R. salexigens-like strains. In addition, phylogenetically, the Rhodothalassium clade represented a distinct lineage and formed a deep branch with less than 90% 16S rRNA gene sequence similarity to other orders of the Alphaproteobacteria, and characteristic phenotypic properties also distinguished these bacteria from other purple non-sulfur bacteria. Therefore, the novel family Rhodothalassiaceae fam. nov. and the novel order Rhodothalassiales ord. nov. are proposed for the distinct phyletic line represented by the genus Rhodothalassium. [Copyright &y& Elsevier]

Abstract: Chlorosomes are light harvesting complexes, interior of which is composed of bacteriochlorophylls that are assembled into lamellar aggregates. In this work, short-range structural parameters of aggregated bacteriochlorophyll-c were explored. The knowledge of bonds involved in aggregation together with other experimental results provides constraints which are satisfied by eight possible structural motifs. Each motif is based on a dimer unit with esterifying alcohols extending to opposite sides of the lamellar layer. The possible models include two of the previously proposed structural models, so-called antiparallel piggy-back dimer [1,2] and a parallel syn-anti model [3]. Structural models of aggregates were built as a single layer consisting of 8×10 monomers and were optimized by Amber program using modified General Amber Force Field. From the optimized models the central tetramer unit was selected for single-point energy analyses. Three electronic methods: RI-MP2/SVP, B97-D/TZVP, and PM6-DH2 were chosen for revealing energy relations in the structural models. Calculations disclose that the most preferable structure is the antiparallel chain model corresponding to the antiparallel piggy-back dimer, followed by one of antiparallel sheet models and one of parallel sheet arrangements. All simulations showed that due to the crystal packing a large deformation of monomeric building block occurred. The deformation energies (the difference between the energy of optimized isolated monomer and that of the monomer in assembled structures) are about 15kcal/mol for all considered computational methods. From energy decomposition, contributions of individual interactions to the overall stabilization energy were estimated. In addition, powder diffraction and optical spectra were calculated for all models and compared with experimental results. [Copyright &y& Elsevier]