X-ray absorption spectroscopy of selenium-containing amino acids

Received: 2 April 1999 / Accepted: 17 September 1999     

Physiological electron donors to the photochemical reaction center of Rhodobacter capsulatus

The nature and number of physiological electron donors to the photochemical reaction center of Rhodobacter capsulatus have been probed by deleting the genes for cytochromes c1 and b of the cytochrome bc1 complex, alone or in combination with deletion of the gene for cytochrome c2. Deletion of cytochrome c1 renders the organism incapable of photosynthetic growth, regardless of the presence or absence of cytochrome c2, because in the absence of the bc1 complex there is no cyclic electron transfer, nor any alternative source of electrons to rereduce the photochemically oxidized reaction center. While cytochrome c2 is capable of reducing the reaction center, there appears no alternative route for its rereduction other than the bc1 complex. The deletion of cytochromes c1 and c2 reveals previously unrecognized membrane-bound and soluble high potential c-type cytochromes, with Em7 = +312 mV and Em6.5 = +316 mV, respectively. These cytochromes do not donate electrons to the reaction center, and their roles are unknown.     

E.p.r.-spectroscopic studies on the molybdenum-iron site of nitrogenase from Clostridium pasteurianum.

The e.p.r. spectroscopy of the nitrogenase molybdenum-iron protein from Clostridium pasteurianum was re-investigated. The sharpness of the delta Ms = +/- 3 g'z peak from the +/- 3/2 Kramer's doublet enables the observation and quantification of incompletely resolved hyperfine splittings from the stable magnetic nuclei 95Mo and 57Fe in samples enriched in these isotopes. No couplings to 1H or 17O could be discerned by examination of spectra from samples exchanged into 2H2O and H2(17)O respectively. Simulation of the spectrum from 95Mo-enriched samples yields a hyperfine coupling of 2.9 MHz, and indicates that the earlier electron-nuclear-double-resonance-derived estimate of 8.1 +/- 0.2 MHz is substantially in error.     

Degradation of synthetic lignins and some lignin monomers by the yeastRhodotorula glutinis

Rhodotorula glutinis degraded variously¹⁴C-labelled synthetic lignins in the presence of 0.1% glucose as co-substrate. Side chain-labelled DHP was degraded the most. While this yeastutilized vanillate and forulate for growth, sinapate/syringate were poorly or not degraded. Gallate, protocatechuate and acetate also supported growth. [carboxy-¹⁴C]Syringate was rapidly converted to¹⁴CO₂ by the yeast only in presence of glucose while [carboxy-¹⁴C]vanillate did not require any additional cosubstrate for mineralization. Ring-labelled vanillyl alcohol was also dagraded proving that the yeast could rapidly metabolize guaiacyl structures while syringyl structures required the presence of additional energy sources.

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Résumé Rhodotorula glutinis dégrade des lignines synthétiques marquées au¹⁴C de manière variée, en présence de 0.1% de glucose comme co-substrat. La DHP marquée sur la chaîne latérale est dégradée le plus. Alors que cette levure utilise le vanillate et le férulate pour sa croissance, le sinapate et le syringate sont peu ou prou dégradables. Le gallate, le protocatéchuate et l'acétate supportent également la croissance. Le syringate marqué au¹⁴C dans sa fonctioncarboxyle estrapidement convert en¹⁴CO₂ par le levure mais exclusivement en présence de glucose, tandis que le vanillate marqué au¹⁴C dans sa fonction carboxyle ne requiert aucun co-substrat additionel pour sa minéralisation. L'alcool vanillique marqué dans son cycle, est également dégradé démonstrant ainsi que la levure peut métaboliser rapidement des structures guaiacyliques tandis que les structures syringiques requièrent la présence de sources auxiliaires d'énergie.

     

Developmental expression of 44-kDa bone phosphoprotein (osteopontin) and bone γ-carboxyglutamic acid (Gla)-containing protein (osteocalcin) in calcifying tissues of rat

New aspects of the distribution and developmental appearance of the 44-kDa bone phosphoprotein (44K BPP, also called sialoprotein I or osteopontin) and bone gamma-carboxyglutamic acid (Gla)-containing protein (BGP, also called osteocalcin) during osteogenesis and dentinogenesis were investigated with immunocytochemical techniques using monospecific, affinity-purified polyclonal antibodies. Sections from newborn rat incisors and from various bone anlagen of newborn animals and fetuses were processed for detection of 44K BPP or BGP antigenicity. In addition, histochemical reactions for detection of alkaline phosphatase or calcium salts were performed on a number of the sections. The 44K BPP appears to be synthesized and secreted by chondrocytes only in the areas of cartilage-to-bone transition; these cells could participate indirectly in the process of bone formation by providing a suitable scaffold onto which primary marrow osteoblasts attach and spread. During osteogenesis, 44K BPP is found in bone-forming cells almost concomitantly with the appearance of alkaline phosphatase and before osteoid deposition, whereas BGP is still absent during early stages of mineralization. We hypothesize that this dramatic difference between the developmental appearance of 44K BPP and BGP reflects the delayed expression of the BGP gene relative to that of 44K BPP. In long-term cultures of bone marrow from adult mice, some fibroblastic cells expressed the 44K BPP phenotype; these cells could represent early osteogenic progenitor cells. Some experiments also suggested that, as with BGP, 44K BPP or an immunologically related protein is synthesized by some odontoblasts and secreted into predentin, prior to the onset of mineralization.     

Use of cloacal sexing techniques in mark-recapture estimates of breeding population size in Wilson's stormpetrel Oceanites oceanicus at South Georgia

Summary Many stormpetrel species breed in habitats where their populations cannot be estimated by direct counts of burrows or birds; mark-recapture experiments have been confounded by the presence of many wandering non-breeders. With a population of Wilson's Stormpetrel Oceanites oceanicus at Bird Island, South Georgia, we tried to estimate the proportion of breeding females in samples obtained during a mark-recapture experiment. These were identified by measurements of the cloaca, which greatly enlarges at egg-laying. A concurrent experiment with individually marked birds determined that breeding females could be discriminated from males and non-breeders for c 30 days after laying. The technique is probably applicable to other petrels, though it will work best with those that lay most synchronously. The overall population estimate was 4841–5515 birds (SE 856–1417); estimates of breeding females gave a population of 2300 paris early in the incubation period and 1400 pairs near hatching.     

Microbial populations and hydrocarbon biodegradation potentials in fertilized shoreline sediments affected by the T/V Exxon Valdez oil spill.

The effort of clean up the T/V Exxon Valdez oil spill in Prince William Sound, Alaska, included the use of fertilizers to accelerate natural microbial degradation of stranded oil. A program to monitor various environmental parameters associated with this technique took place during the summer of 1990. Microbiological assays for numbers of heterotrophic and oil-degrading microbes and their hydrocarbon mineralization potentials were performed in support of this program. Fertilizer addition resulted in higher hexadecane and phenanthrene mineralization potentials on treated plots than on untreated reference plots. Microbial numbers in treated and reference surface sediments were not significantly different immediately after the first nutrient application in May 1990. However, subsurface sediments from treated plots had higher numbers of hydrocarbon degraders than did reference sediments shortly after treatment. The second application of fertilizer, later in summer, resulted in surface and subsurface increases in numbers of hydrocarbon degraders with respect to reference sediments at two of the three study sites. Elevated mineralization potentials, coupled with increased numbers of hydrocarbon degraders, indicated that natural hydrocarbon biodegradation was enhanced. However, these microbiological measurements alone are not sufficient to determine in situ rates of crude oil biodegradation.     

Biodegradation of textile azo-dyes byPhanerochaete chrysosporium

Of 18 commercially used textile dyes, eight were degraded by the white rot fungus,Phanerochaete chrysosporium, by 40 to 73% based on decrease of colour. Both the lignin-degrading enzyme system ofP. chrysosporium and adsorption to its cell mass were involved in the degradation of the diazo dye, Reactofix Gold Yellow. Degradation was best achieved by adding the dye to the medium and then inoculating with pre-grown mycelium; inoculation with spores resulted mainly in dye adsorption.     

Predictive model of conjugative plasmid transfer in the rhizosphere and phyllosphere.

A computer simulation model was used to predict the dynamics of survival and conjugation of Pseudomonas cepacia (carrying the transmissible recombinant plasmid R388:Tn1721) with a nonrecombinant recipient strain in simple rhizosphere and phyllosphere microcosms. Plasmid transfer rates were derived for a mass action model, and donor and recipient survival were modeled as exponential growth and decay processes or both. Rate parameters were derived from laboratory studies in which donor and recipient strains were incubated in test tubes with a peat-vermiculite solution or on excised radish or bean leaves in petri dishes. The model predicted donor, recipient, and transconjugant populations in hourly time steps. It was tested in a microcosm planted with radish seeds and inoculated with donor and recipient strains and on leaf surfaces of radish and bean plants also growing in microcosms. Bacteria were periodically enumerated on selective media over 7 to 14 days. When donor and recipient populations were 10(6) to 10(8) CFU/g (wet weight) of plant or soil, transconjugant populations of about 10(1) to 10(4) were observed after 1 day. An initial rapid increase and a subsequent decline in numbers of transconjugants in the rhizosphere and on leaf surfaces were correctly predicted.