Two pathways of electron transport to nitrogenase in Rhodospirillum rubrum: the major pathway is dependent on the fix gene products

In the photosynthetic bacterium Rhodospirillum rubrum, as in many other diazotrophs, electron transport to nitrogenase has not been characterized in great detail. In this study, we show that there are two pathways operating in R. rubrum. The products of the fix genes constitute the major pathway operating under heterotrophic conditions, whereas a pyruvate:ferredoxin oxidoreductase, encoded by the nifJ gene, may play a central role under anaerobic conditions in the dark. In both systems, ferredoxin N is the main direct electron donor to dinitrogenase reductase. Furthermore, we suggest from studying mutants lacking components in one or both systems under different conditions, that the Fix system operates most efficiently under conditions when a proton motive force is generated. A model for our current view of the electron transfer pathways in R. rubrum is presented.     

红色诺卡氏菌细胞壁骨架对小鼠肝癌细胞生长的抑制效果

目的:通过构建H22荷瘤小鼠模型,观察红色诺卡氏菌细胞壁骨架(Nocardia Rubra Cell Wall Skeleton,N-CWS)对H22荷瘤小鼠肝癌细胞生长的抑制效果。方法:复苏并培养H22细胞,将H22细胞以皮下方式接种到小鼠右侧腋部,建立H22荷瘤小鼠肝癌模型,随机分为对照组(生理盐水组)、低浓度N-CWS组(400μg/m L)与高浓度N-CWS组(800μg/m L),分别灌胃1次/d,共灌胃14 d,最长接种肿瘤15 d后处死小鼠,观察肝癌细胞的大小和重量。结果:治疗组小鼠肿瘤质量明显低于对照组(1.46±0.16)g,且高浓度组小鼠肿瘤质量(0.52±0.13)g明显低于低浓度组(0.79±0.13)g,组间对比差异有统计学意义(P0.05)。在治疗第3 d起直至结束,治疗组小鼠肿瘤体积均明显低于对照组,从第5 d起直至结束,高浓度组小鼠肿瘤体积明显低于低浓度组(P0.05)。第5 d起至结束,治疗组小鼠肿瘤体积增长的变化明显缓于对照组(P0.05)。高浓度组小鼠肿瘤体积的增长在第5 d后明显缓于低浓度组(P0.05)。对照组在第9 d时,增长变化最为显著,较第7 d增加约400 mm3。低浓度组变化较稳定。高浓度组肿瘤增长明显变缓,第7 d后最为明显,后逐渐趋于缓和。结论:N-CWS可以明显抑制肿瘤生长,且高浓度N-CWS抑制肿瘤生长效果更佳。     

Glucose feeding results in coordinated changes of chlorophyll content, ribulose-1,5-bisphosphate carboxylase-oxygenase activity and photosynthetic potential in photoautrophic suspension cultured cells of Chenopodium rubrum

The effects of an excessive supply of carbohydrates on the photosynthetic apparatus of photoautotrophic suspension cultured cells of Chenopodium rubrum were analysed. Glucose feeding resulted in a massive intracellular accumulation of carbohydrates (glucose, fructose, sucrose and starch) and a delayed but pronounced reduction of the chlorophyll content. Maximum photosynthetic efficiency (determined as relative photon yield of oxygen evolution or calculated from fluorescence parameters) was only slightly affected by this treatment. The maximum values of photosynthetic oxygen evolution and of ribulose-1,5-bisphosphate carboxylase-oxygenase activity also did not change significantly when expressed on a chlorophyll basis, thus indicating that membrane and stroma components were reduced to the same extent. Growth analysis demonstrated that even with an excessive supply of carbohydrates the contribution of photosynthesis to growth was still significant (about 35% of total DW production). The results support the hypothesis that accumulation of carbohydrates leads to a coordinated reduction of the photosynthetic machinery. Comparable changes possibly occur during source/sink transitions in green plant tissues.     

Variability in host-plant quality for the larvae of a polyphagous insect folivore in midseason: the impact of light on three deciduous sapling species

We examined the effects of light availability on the suitability of foliage from red maple (Acer rubrum L.) (Aceraceae), black cherry (Prunus serotina Ehrhart) (Rosaceae), and sassafras [Sassafras albidum (Nuttall) Nees (Lauraceae)] for the larvae of the promethea moth, Callosamia promethea Drury (Lepidoptera: Saturniidae), in midseason. We identified replicate sun- and shade-grown saplings of red maple, black cherry, and sassafras from naturally growing populations in the field. Foliage collected from the experimental saplings was bioassayed using early instars of the promethea moth and assayed for nitrogen and carbon content. Promethea moth-larval performance and survivorship was highest on sassafras, intermediate on black cherry, and lowest on red maple. Larvae feeding on foliage from plants grown in the sun performed better than from those grown in the shade; the effect of light did not depend on sapling species. Foliar nitrogen content varied among the sapling species and was higher, overall, in foliage from plants grown in the sun. Nitrogen concentration related strongly and positively with larval performance and accounted for a great deal of the variation in performance both among the sapling species and between the sun and shade treatments. During midseason, foliar nitrogen content is determined by light availability, it varies among sapling species, and it is likely the primary constituent determining host quality for folivores on these sapling species.     

The activator of the Rhodospirillum rubrum PHB depolymerase is a polypeptide that is extremely resistant to high temperature (121 degrees C) and other physical or chemical stresses

Hydrolysis of native (amorphous) polyhydroxybutyrate (nPHB) granules isolated from different sources by soluble PHB depolymerase of Rhodospirillum rubrum in vitro requires the presence of a heat-stable compound (activator). The activator was purified and was resistant against various physical and chemical stresses such as heat (up to 130 degrees C), pH 1-12, dryness, oxidation by H2O2, reducing and denaturing compounds (2-mercaptoethanol, 5 M guanidinium-HCl) and many solvents including phenol/chloroform. The activator coding gene was identified by N-terminal sequencing of the purified protein, and the deduced protein showed significant homology to magnetosome-associated protein (Mms16) of magnetotactic bacteria. Analysis of the activation process in vitro showed that the activator acts on nPHB granules but not on the depolymerase. The effect of the activator could be mimicked by pretreatment of nPHB granules with trypsin or other proteases but protease activity of the purified activator was not detected. Evidence is shown that different mechanisms were responsible for activation of nPHB by trypsin and activator, respectively. PHB granule-associated protein (PhaP) of Ralstonia eutropha nPHB granules were cleaved by trypsin but no cleavage occurred after activator treatment. Hydrolysis of artificial protein-free PHB granules coated with negatively charged detergents (sodium dodecyl sulfate (SDS), cholate but not cetyltrimethyl-ammonium bromide (CTAB)) did not require activation and confirmed that surface layer proteins of nPHB granules are the targets of the activator rather than lipids. All experimental data are in agreement with the assumption that trypsin and the activator enable the PHB depolymerase to find and to bind to the polymer surface: trypsin by removing a portion of proteins from the polymer surface, the activator by modifying the surface structure in a not yet understood manner presumably by interaction with phasins of the proteinous surface layer of nPHB.     

Amino acid- or protein-dependent growth of Trichophyton mentagrophytes and Trichophyton rubrum

Culture conditions were examined for Trichophyton mentagrophytes and Trichophyton rubrum, which are major pathogens involved in dermatophytosis. They grew well in Sabouraud's dextrose broth or RPMI 1640. Growth in phosphate-buffered yeast nitrogen base supplemented with glucose was very slow, although growth improved significantly with the addition of amino acids or proteins to the medium. The fungi could also grow using human nail fragments as the only source of nutrition. Examination of proteases by substrate gel electrophoresis indicated that distinct sets of proteases are secreted from the dermatophytes in two different media, Sabouraud's dextrose broth and nail fragments. A protease inhibitor, phenylmethanesulfonyl fluoride, inhibited the growth of the fungi on nail fragments, but it did not inhibit their growth in Sabouraud's dextrose broth.     

Homoserine kinase from the phototrophic bacterium Rhodospirillum rubrum is not sensitive to feedback inhibition by l-threonine

Abstract Homoserine kinase (EC 2.7.1.39), one of the enzymes of L -threonine synthesis, was purified 200-fold from the phototrophic bacterium Rhodospirillum rubrum strain S1 by salt precipitation, hydrophobic interaction chromatography and gel filtration. The enzyme had a M _r of about 145000 and was active with L -homoserine ( K _m= 3 mM) and ATP ( K _m= 0.44 mM). In contrast to the kinase from the enteric bacterium, Escherichia coli , the R. rubrum enzyme was neither stabilized nor inhibited by L -threonine. Of 18 amino acids and metabolites tested (including L -allo-threonine, D -allo-threonine, DL -homocysteine, o -phosphoserine and L -norleucine), none was found to be inhibitory.     

Differences between tree species in hydraulic press calibration of leaf water potential are correlated with specific leaf area

Abstract To determine the usefulness of the J-14 Hydraulic Press (Campbell Scientific, Inc., Logan, Utah, U.S.A.) in estimating leaf water potential, we calibrated the J-14 Press against a Scholander-type pressure chamber for leaves of various tree species. The species tested were: Acer saccharum, Acer negundo, Acer rubrum. Populus tremuloides, Populus grandidentata, Quercus rubra, and Brassaia actinophylla (Schefflera). The regression calibrations were linear with standard errors about the regression less than 0.1 MPa. The regression equations for the four genera were significantly different, with the y- intercept increasing and the slope decreasing in order of decreasing specific leaf area (SLA). There were no significant differences between species of the calibration lines within the genera Acer and Populus. These data may indicate that leaves with lower SLA resist mechanical compression by the hydraulic press, causing the J-14 Press to be less sensitive to differences of leaf water potential. Therefore the J-14 Press is only a relative measure of leaf water status and does not measure leaf water potential.     

Deep dermatophytosis caused by Trichophyton rubrum – A case report

A case of deep dermatophytosis in the gluteal region in a male patient successfully treated with terbinafine is described with its clinical, mycological and histopathological features. This revised version was published online in June 2006 with corrections to the Cover Date.     

Photoperiodic control of cytokinin transport and metabolism in Chenopodium rubrum

Cytokinin (CK) levels in the short-day plant Chenopodium rubrum L. are known to fluctuate diurnally. The aim of this work was to investigate if the diurnal changes are brought about by changes in transport and/or metabolism of CKs. The effect of photo-period on cytokinin transport was studied by analysing CK concentrations in root, leaf and apical exudates, respectively, under constant light (CL), a 12-h photoperiod (DL) inductive for flowering, DL in which darkness was interrupted at the end of hour 6 by 15 min red light (R), or by 15 min R followed by 30 min far-red irradiation (R/FR). The concentrations of cytokinins (zeatin, zeatin riboside, isopentenyladenine, isopen-tenyladenosine) in all three types of exudates were significantly higher in the first 12-h period after the end of 12 h darkness than in CL. The R break almost fully negated the effect of darkness and its effect was reversed by FR, showing the involvement of phytochrome in the regulation of CK transport. In the next 12-h interval, i.e. 12–24 h after the end of darkness, the CK level remained high in the leaf exudate only, but to a much lower extent than in the previous 12 h. The highest CK concentration (increase by 108%) was observed in apical exudates during inductive darkness. A comparison of the CKs present in the individual exudates indicates that those arriving at the apical part are derived mostly from leaves with varying contributions by the xylem. The metabolism of applied [³H]-zeatin riboside (ZR) was studied using HPLC separation of the metabolites. Metabolism was found to be very rapid and different glucosides, adenine and adenosine were the main metabolites after 12 h incubation with labelled ZR in all regimes tested. The only metabolite that seems to be under photoperiodic control is ZR-5′-monophosphate. It is as yet not clear if photoperiod controls the phosphorylation or dephosphorylation reaction. The activity of the main cytokinin degradative enzyme, cytokinin oxidase, did not change during the photoperiodic regimes tested.