Membrane preparations of two species of the green sulfur bacteria Chlorobium have been studied by EPR. Three signals were detected which were attributed to iron-sulfur centers acting as electron acceptors in the photosynthetic reaction center. (1) A signal from a center designated FB, (gz = 2.07, gy = 1.91, gx = 1.86) was photoinduced at 4 K. (2) A similar signal, FA (gz = 2.05, gy = 1.94, gx = 1.88), was photoinduced in addition to the FB signal upon a short period of illumination at 200 K. (3) Further illumination at 200 K resulted in the appearance of a broad feature at g = 1.78. This is attributed to the gx component of an iron-sulfur center designated FX. The designations of these signals as FB, FA, and FX are based on their spectroscopic similarities to signals in photosystem I (PS I). The orientation dependence of these EPR signals in ordered Chlorobium membrane multilayers is remarkably similar to that of their PS I homologues. A magnetic interaction between the reduced forms of FB and FA occurs, which is also very similar to that seen in PS I. However, in contrast to the situation in PS I, FA and FB cannot be chemically reduced by sodium dithionite at pH 11. This indicates redox potentials for FA and FB which are lower by at least 150 mV than their PS I counterparts. The triplet state of P840, the primary electron donor, could be photoinduced at 4 K in samples which had been preincubated with sodium dithionite and methyl viologen and then preilluminated at 200 K.(ABSTRACT TRUNCATED AT 250 WORDS)

Reaction center photochemistry in Heliobacterium chlorum has been investigated by using EPR and flash absorption spectroscopy at low temperatures. The following results were obtained. At 5 K, in the presence of ascorbate, continuous illumination resulted in the formation of P798+ and a reduced iron-sulfur center designated FB (gz = 2.07, gy = 1.93, gx = 1.89). This state was stable at low temperatures, but the yield for this reaction was low, and it was estimated that it occurred only in about 3% of the centers upon the first flash. After continuous illumination of a dilute sample for 10 min, still only half of the centers attained this state. In most centers, flash excitation at 5 K produced a state which recombined with time constants of 2.5 ms (congruent to 80%) and 850 microseconds (congruent to 20%). These two phases were differently influenced by the redox state of the reaction center, indicating that two different acceptors were involved in the recombination reactions. When continuous illumination was given at 200 K, a second center, designated FA, was additionally reduced (gz = 2.05, gy = 1.95, gx = 1.90). High concentrations of dithionite resulted in the chemical reduction of FB and of most of FA; illumination at 200 K resulted in the further reduction of FA. Two triplet states were identified by EPR and optical spectroscopy. The amplitude of the narrower triplet (magnitude of D = 226 x 10(-4) cm-1) varied with the redox state of the iron-sulfur centers and was influenced by a component thought to be a quinone undergoing double reduction. It correlated with a triplet state observed by flash absorption spectroscopy showing a bleaching at 798 nm and is attributed to a triplet state formed by charge recombination in the reaction center. Its narrowness is taken as an indication of its origin on a pair of bacteriochlorophylls, and its orientation indicates an orientation of the chlorophyll ring plane perpendicular to the membrane plane. The second triplet had a wider splitting (magnitude of D = 242 x 10(-4) cm-1), did not vary systematically with redox conditions, corresponds to an optical spectrum with a maximum at 812 nm, and is not ordered in the membrane. It was thus attributed to a triplet located on a BChl g monomer in the antenna. The reaction center photochemistry in H. chlorum is comparable in many respects to that of photosystem I and green sulfur bacteria. Earlier contrasting conclusions are discussed and rationalized in light of the present results.

A photosynthetic reaction center complex was prepared from the green sulfur bacterium Chlorobium by solubilization of chlorosome-depleted membranes with lauryl maltoside, followed by anion-exchange chromatography and molecular sieve chromatography. The purified complex was characterized by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, optical spectroscopy, and EPR spectroscopy.The major bands migrated at apparent molecular masses of 50,42, and 32 kDa (hemestainiig) and additional weaker bands at 22, 15, and 12 kDa. The isolated reaction center complex contained about 40 bacteriochlorophyll a molecules per primary electron donor, Pg40, assayed by photooxidation. It was competent in stable low-temperature photoreduction of the FeS centers FA and FB. The spectra of these acceptors and their low-temperature photochemistry in the purified complex were the same as found in intact Chlorobium membranes and similar to what had been described for photosystem I from plants. Membrane-bound cytochrome c553 copurified with the reaction center complex.

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An asymmetric EPR-line with a g factor of 2.0045 was detected after phototrapping at 196 K in membranes and in isolated photoactive P840 reaction centers of Chlorobium limicola f. thiosulfatophilum. The spectra resemble those of the electron acceptor A; of photosystem I in chloroplasts and cyanobacteria. At 229 K a symmetric signal at g=2.0033, comparable to the one of the early electron acceptor &, is additionally phototrapped. In contrast to membranes, the reaction center preparation does not contain appreciable amounts of photoreducible FeS-centers.

Abstract-A sediment contact test (SCT) battery consisting of five ecotoxicological test systems was applied to 21 native freshwater sediments characterized by a broad variety of geochemical properties and anthropogenic contamination. Higher plants (Myriophyllum aquaticum), nematodes (Caenorhabditis elegans), oligochaetes (Lumbriculus variegatus), zebrafish embryos (Danio rerio), and bacteria (Arthrobacter globiformis), representing various trophic levels and exposure pathways, were used as test organisms. The test battery detected sediment toxicity caused by anthropogenic pollution, whereas the various tests provided site-specific, nonredundant information to the overall toxicity assessment. Based on the toxicity pattern derived from the test battery, the sediments were classified according to a newly proposed classification system for sediment toxicity assessment. The SCT-derived classification generally agreed well with the application of consensus-based sediment quality guidelines (SQGs), especially with regard to sediments with high toxic potential. For sediments with low to medium toxic potential, the SQGs often underestimated the toxicity that was detected by the SCTs, underpinning the need for toxicity tests in sediment quality assessment. Environ. Toxicol. Chem. 2013;32:144-155. # 2012 SETAC

Soret resonance and Q, preresonance Raman spectra are reported and compared for a series of (bacterio)chlorophylIs. Chlorophyll a, 2-acetylchlorophyll a, bacteriochlorophyll a and 2-vinylbacteriochlorophyll a were studied in the non-protic solvent tetrahydrofuran. These experiments were designed to identify Raman bands corresponding to the stretching mode@) of the vinyl group at the C-2 position of ring I of chlorophyll a and 2-vinylbacteriochlorophyll a, and to ascertain whether additional bands corresponding to C, C, and/or C, C, vibrations could be observed in the 1615-1660 cm-' region. Raman spectra of chlorophyll u and 2-vinylbacteriochlorophyll a exhibit a 1625 cm-' band, which is absent from the Raman spectra of 2-acetylchlorophyll u and bacteriochlorophyll a. It is assigned to the vC,,C,, mode of the vinyl group. No other band can be definitively assigned to any mode predominantly arising from vinyl motions. The acetyl-containing molecules 2-acetylchlorophyll a and bacteriochlorophyll a give rise to a cu. 1070 cm-' band, which appears to be related to the presence of the acetyl substituent. The 1615-1660 cm-' region of the Raman spectra of all four derivatives did not contain any additional band which could be ascribed to modes involving the vC,C, and/or vC, C, coordinates.