Dynamical simulation of the optical response of photosynthetic pigments.

From time integration of the electron dynamics under a density functional tight binding Hamiltonian in the presence of external time varying electric fields, we obtain the absorption spectra of a series of chlorophylls and bacteriochlorophylls. We obtain good agreement with the observed experimental energies as well as with fully ab initio results in the literature for the main absorption bands. As a first step towards an atomistic description of energy transfer between chromophores in photosynthetic antenna systems we calculate the coupling energy between the excitations of two chlorophyll a molecules as a function of the distance as well as the transfer of energy between these when one of them is subjected to laser illumination.

Characterization of a mutant strain of Rhodovulum sulfidophilum lacking the pufA and pufB genes encoding the polypeptides for the light-harvesting complex 1 (B 870).

Contradictory results on the effectiveness of energy transfer from the light harvesting complex 2 (LH2) directly to the reaction center (RC) in mutant strains lacking the core light-harvesting complex 1 (LH1) have been obtained with cells of Rhodobacter capsulatus and Rhodobacter sphaeroides. A LH1(-) mutant of Rhodovulum sulfidophilum, named rsLRI, was constructed by deletion of the pufBA genes, resulting in a kanamycin resistant photosynthetically positive clone. To restore the wild type phenotype, a complemented strain C2 was constructed by inserting in trans a DNA segment containing the pufBA genes. Light-induced FTIR difference spectra indicate that the RC in the rsLRI mutant and in the C2 complemented strains are functionally and structurally identical with those in the wild type strain, demonstrating that the assembly and the function of the RC is not impaired by the LH1 deletion. The photosynthetic growth rate of the rsLRI strain increased with decreasing light intensity. At 50 W m(-2 )no photosynthetic growth was observed. These results indicate that the light energy harvested by the LH2 complex was not or inefficiently transferred to the RC; thus most of the energy necessary for photosynthetic growth is in the LH1(-) strain directly absorbed by the RC. It is supposed that in the mutant strain, RC and LH2 cannot interact in an efficient way.

Phosphorylation of LHI beta during membrane synthesis in the photosynthetic bacterium Rhodovulum sulfidophilum.

Cells of Rhv. sulfidophilum were grown under different conditions in the presence of 32P-phosphate and the corresponding H and L membrane fractions obtained and fractionated by SDS-PAGE. Both membranes showed almost identical polypeptide composition. The bacteriochlorophyll (Bchl) specific content in H was always lower that in L. As described before, oxygen did not regulate gene expression. Under high light, an almost two- to threefold decrease of the cellular specific Bchl content was observed. Pulse and chase experiments showed that transitions from aerobiosis to light-anaerobiosis did not quantitatively affect the Bchl content of the membranes, although a turnover of the 32P-phosphate and 35S-methionine was observed. LHI beta was the only polypeptidic subunit of the Bchl-binding polypeptides that was phosphorylated in vivo, and phosphotyrosine was the only phosphorylated amino acid detectable. The phosphorylated LHI beta was determined to be insoluble in the organic solvent mixture of (vol/vol) 1:1 chloroform-methanol containing ammonium acetate (0.1 m final concentration). Treatment with a chaotropic agent such as Na2CO3 solubilized the phosphorylated LHI beta, indicating that part of this posttranslationally modified polypeptide was not inserted in a transmembrane position. These results were used to speculate about the regulatory properties of this posttranslational modification of LHI beta on membrane differentiation.

Estudo sobre a utilizaçäo de bactérias fotossintéticas no tratamento de resíduos orgânicos / Use study of red anoxygenic photosyntetic bacteria in organic effluents treatment systems

Estudou-se a utilizaçäo de bactérias fotossintéticas anoxigênicas vermelhas em sistemas de tratamento de efluentes orgânicos. O experimento foi conduzido num reator anaeróbio de acrílico transparente com capacidade de 55 litros. O resíduo orgânico utilizado para alimentaçäo do reator foi o efluente de um biodigestor anaeróbio tratando vinhaça instalado na CETESB. O inóculo utilizadeo foi preparado a partir da cultura de bactérias fotossintéticas isoladas do sedimento do córrego do Sapateiro (Säo Paulo). O sistema foi operado durante 107 dias sendo que a carga orgânica média aplicada do 1§ ao 72§ dia de ensaio foi de 31g DQO. dia *-1 e do 73§ ao 107§ dia de 42g DQO. dia*-1. Foram efetuadas análises para avaliaçäo de matéria orgânica no resíduo e contagens de bactérias fotossintéticas vermelhas. Desenvolveu-se metodologia para cultivo maçiço de bactérias fotossintéticas vermelhas em laboratório, selecionando a técnica de "roll-tube" para sua quantificaçäo. A taxa média de crescimentoo das bactérias fotossintéticas no sistema foi de 0,178 dia*-1. A eficiência média de remoçäo de matéria orgânica do resíduo expressa em Demanda Química de Oxigênio (DQO) e Demanda Bioquímica de Oxigênio (DBO) foi aproximadamente 20 por cento e 50 por cento respectivamente

Analysis of lipophilic pigments from a phototrophic microbial mat community by high performance liquid chromatography.

As assay for lipophilic pigments in phototrophic microbial mat communities using reverse phase-high performance liquid chromatography was developed which allows the separation of 15 carotenoids and chloropigments in a single 30 min program. Lipophilic pigments in a laminated mat from a commercial salina near Laguna Guerrero Negro, Baja California Sur, Mexico reflected their source organisms. Myxoxanthophyll, echinenone, canthaxanthin, and zeaxanthin were derived from cyanobacteria; chlorophyll c, and fucoxanthin from diatoms; chlorophyll a from cyanobacteria and diatoms; bacteriochlorophylls a and c, bacteriophaeophytin a, and gamma-carotene from Chloroflexus spp.; and beta-carotene from a variety of phototrophs. Sensitivity of detection was 0.6-6.1 ng for carotenoids and 1.7-12 ng for most chloropigments. This assay represents a significant improvement over previous analyses of lipophilic pigments in microbial mats and promises to have a wider application to other types of phototrophic communities.

Optical properties of benthic photosynthetic communities: fiber-optic studies of cyanobacterial mats.

A fiber-optic microphobe was used to analyze the spectral light gradients in benthic cyanobacterial mats with 50-micrometer depth resolution and 10-nm spectral resolution. Microcoleus chthononplastes mats were collected from hypersaline, coastal ponds at Guerrero Negro, Baja California. Gradients of spectral radiance, L, were measured at different angles through the mats and the spherically integrated scalar irradiance, Eo, was calculated. Maximal spectral light attenuation was found at the absorption peaks for the dominant photosynthetic pigments: chlorophyll a at 430 and 670 nm, carotenoids at 450-500 nm, phycocyanin at 620 nm, and bacteriochlorophyll a at 800-900 nm. Scattered light had a marked spectral effect on the scalar irradiance which near the mat surface reached up to 190% of the incident irradiance. The spherically integrated irradiance thus differed strongly from the incident irradiance both in total intensity and in spectral composition. These basic optical properties are important for the understanding of photosynthesis and light harvesting in benthic and epiphytic communities.

[Adaptation of Rhodopseudomonas palustris to changes in atmospheric conditions]. / Adaptación de Rhodopseudomonas palustris a cambios de condiciones atmosféricas.

The high level of delta-aminolaevulinate synthetase (ALA-S) in Rhodopseudomonas palustris cells grown under photosynthetic conditions decreased when they were vigorously aerated; moreover, the bacteriochlorophyll synthesis suddenly stopped. When aeration was interrupted, enzymatic level increased notably, but bacteriochlorophyll level did not. Chloramphenicol added to cultures when aeration was interrupted did not affect the increase of enzymic level. When it was added as the aeration started, the enzymic level decayed, but did not increase as notably when the aeration was interrupted. ALA-S in extracts of aerated cells underwent spontaneous activation when homogenates were stored at 4 degrees C. The effect of several activators on different forms of ALA-S is postulated in order to explain these findings.

Adaptación de Rhodopseudomonas palustris a cambios de condiciones atmosféricas / Adaptation of Rhodopseudomonas palustris to changes in atmospheric conditions

El burbujeo de O2 95%-N2 5% a un cultivo de Rhodopseudomonas palustris crecido en condiciones fotosintéticas provoca un cese inmediato de la síntesis de bacterioclorofila y una disminución de la actividad de la enzima delta-aminolevulinato sintetasa (ALA-S), sin alterar el crecimiento bacteriano. Al cesar el gaseado el nivel enzimático se recupera rápidamente pero el de bacterioclorofila lo hace más lentamente. El agregado de cloramfenicol al cesar el gaseado, no afecta la recuperación de la actividad enzimática. En cambio, si se lo agrega desde el inicio del gaseado, la actividad igual decae pero su recuperación es menor que en ausencia del antibiótico. La enzima de extractos de células gaseadas muestra activación espontánea a 40-C Se postula el efecto de distintos activadores sobre diversas formas de la enzima ALA-S para explicar estos hechos

Adaptación de Rhodopseudomonas palustris a cambios de condiciones atmosféricas / Adaptation of Rhodopseudomonas palustris to changes in atmospheric conditions

El burbujeo de O2 95%-N2 5% a un cultivo de Rhodopseudomonas palustris crecido en condiciones fotosintéticas provoca un cese inmediato de la síntesis de bacterioclorofila y una disminución de la actividad de la enzima delta-aminolevulinato sintetasa (ALA-S), sin alterar el crecimiento bacteriano. Al cesar el gaseado el nivel enzimático se recupera rápidamente pero el de bacterioclorofila lo hace más lentamente. El agregado de cloramfenicol al cesar el gaseado, no afecta la recuperación de la actividad enzimática. En cambio, si se lo agrega desde el inicio del gaseado, la actividad igual decae pero su recuperación es menor que en ausencia del antibiótico. La enzima de extractos de células gaseadas muestra activación espontánea a 40-C Se postula el efecto de distintos activadores sobre diversas formas de la enzima ALA-S para explicar estos hechos (AU)

[Effect of light intensity on the biosynthesis of bacteriochlorophylls in Rhodomicrobium vannielii and Rhodopseudomonas palustris]. / Efecto de la intensidad luminosa sobre la biosíntesis de bacterioclorofila en Rhodomicrobium vannielii y Rhodopseudomonas palustris.

The activity of aminolevulinate-synthetase in crude extracts of R. vannielii was determined. Its properties are very similar to those of the enzyme from R. palustris. With increasing light intensity on cultures of both microorganisms, their specific growth rates increases and the concentration of bacteriochlorophyll decreases. ALA-synthetase exhibits a dual-pattern; its activity remains at a high constant level up to 4 x 10(4) erg cm-2 seg-1, decreasing at higher light intensities (Figures 1 and 2). The activity of succinil-CoA-synthetase of both microorganisms and ALA-dehydrase of R. palustris remain constant over the entire range of light intensities used, but the ALA-dehydrase of R. vannielii shows the same dual-pattern as ALA-synthetase (Table 1), namely a constant high level at the lower light intensities, decreasing at the higher ones. With dialysis the activity of ALA-synthetase of both microorganisms decreases only in extracts from low light intensity grown bacteria, while it did not decrease in extracts from bacteria grown at high light intensities.