Mycoplasmas are minimal, wall-less bacteria but have retained the ability to secrete complex carbohydrate polymers that constitute a glycocalyx. In members of the Mycoplasma mycoides cluster, which ...are important ruminant pathogens, the glycocalyx includes both cell-attached and cell-free polysaccharides. This report explores the potential secretion of polysaccharides by M. agalactiae, another ruminant pathogen that belongs to a distant phylogenetic group. Comparative genomic analyses showed that M. agalactiae possesses all the genes required for polysaccharide secretion. Notably, a putative synthase gene (gsmA) was identified, by in silico reconstruction of the biosynthetic pathway, that could be involved in both polymerization and export of the carbohydrate polymers. M. agalactiae polysaccharides were then purified in vitro and found to be mainly cell attached, with a linear β-(1...6)-glucopyranose structure β-(1...6)-glucan. Secretion of β-(1...6)-glucan was further shown to rely on the presence of a functional gsmA gene, whose expression is subjected to high-frequency phase variation. This event is governed by the spontaneous intraclonal variation in length of a poly(G) tract located in the gsmA coding sequence and was shown to occur in most of the M. agalactiae clinical isolates tested in this study. M. agalactiae susceptibility to serum-killing activity appeared to be dictated by ON/OFF switching of β-(1...6)-glucan secretion, suggesting a role of this phenomenon in survival of the pathogen when it invades the host bloodstream. Finally, β-(1...6)-glucan secretion was not restricted to M. agalactiae but was detected also in M. mycoides subsp. capri PG3T, another pathogen of small ruminants. (ProQuest: ... denotes formulae/symbols omitted.)
Tadmor is a Syrian barley landrace that has adapted to semi‐arid environments. Its leaves are pale green because of a 30% decrease in the chlorophyll and the carotenoid content of the chloroplasts ...(leading to a 7·5% decrease in light absorption) compared with barley genotypes that are not adapted to harsh Mediterranean climatic conditions (e.g. Plaisant). This difference in pigment content was attenuated during growth of the plants in strong light, but was strongly amplified when strong light was combined with a high growth temperature. The low pigment content of Tadmor leaves was not associated with significant changes in the pigment distribution between the photosystems or between the reaction centres of the photosystems and their associated chlorophyll antennae. No significant difference in the photosynthetic activity (O2 production per unit absorbed light) was observed between Tadmor and Plaisant. The conversion of violaxanthin to zeaxanthin in strong light and its reversal in darkness were much faster and operated at a higher capacity in Tadmor leaves compared with Plaisant leaves, resulting in an increased photostability of photosystem II in the former leaves. The accelerated xanthophylls interconversion in the Syrian landrace was associated with, and possibly related to, an increased fluidity of the thylakoid membranes. The lipid peroxide level was lower in Tadmor compared with Plaisant. In contrast, no difference was found in the non‐photochemical quenching of chlorophyll fluorescence between the two barley genotypes. The data indicate that the pale green Syrian landrace is equipped to survive excessive irradiance through a passive reduction of the light absorptance of its leaves, which mitigates the heating effects of strong light, and through the active protection of its photochemical apparatus by a rapid xanthophyll cycling.
AIM To study the effect of superselective ophthalmic artery fibrinolysis as a treatment for central retinal vein occlusion (CRVO). METHODS Retrospective, university based single centre study. The ...charts of 26 eyes of 26 patients treated were reviewed. Among the 26 patients, there were nine cases of combined artery and vein occlusion, three cases of combined cilioretinal artery and CRVO, and 14 cases of classic CRVO. Complete preoperative and postoperative ophthalmological examination and fluorescein angiography were performed in all cases. The therapeutic procedure comprised the infusion of urokinase through a microcatheter into the ostium of the ophthalmic artery, via a femoral artery approach. The main outcome measure was the improvement in visual acuity 48 hours after the procedure. RESULTS Six eyes of six patients exhibited significant improvement in visual acuity immediately after the fibrinolysis procedure. Among them, four had a initial funduscopic appearance suggestive of combined occlusion of the central retinal artery (CRAO) and vein. For these patients, the visual benefit was maintained in the long term. Intravitreal haemorrhage occurred in two patients. There were no extraocular complications linked to the procedure. CONCLUSIONS Selective ophthalmic artery infusion of urokinase was followed by improvement in VA in six out of 26 cases of CRVO. Eyes with combined CRAO and CRVO with recent visual loss appeared to be the most responsive. This treatment did not prevent the occurrence of ischaemia in the failure cases. The efficacy of in situ fibrinolysis for treatment of CRVO needs to be further evaluated in a controlled study.
Moderately elevated temperatures induce a rapid increase in the heat and light resistance of photosystem II (PSII) in higher-plant leaves. This phenomenon was studied in intact potato leaves exposed ...to 35 degrees C for 2 h, using chlorophyll fluorometry, kinetic and difference spectrophotometry and photoacoustics. The 35 degrees C treatment was observed to cause energetic uncoupling between carotenoids and chlorophylls: (i) the steady-state chlorophyll fluorescence emission excited by a blue light beam (490 nm) was noticeably reduced as compared to fluorescence elicited by orange light (590 nm) and (ii) the quantum yield for photosynthetic oxygen evolution in blue light (400-500 nm) was preferentially reduced relative to the quantum yield measured in red light (590-710 nm). Analysis of the chlorophyll-fluorescence and light-absorption characteristics of the heated leaves showed numerous analogies with the fluorescence and absorption changes associated with the light-induced xanthophyll cycle activity, indicating that the carotenoid species involved in the heat-induced pigment uncoupling could be the xanthophyll violaxanthin. More precisely, the 35 degrees C treatment was observed to accelerate and amplify the nonphotochemical quenching of chlorophyll fluorescence (in both moderate red light and strong white light) and to cause an increase in leaf absorbance in the blue-green spectral region near 520 nm, as do strong light treatments which induce the massive conversion of violaxanthin to zeaxanthin. Interestingly, short exposure of potato leaves to strong light also provoked a significant increase in the stability of PSII to heat stress. It was also observed that photosynthetic electron transport was considerably more inhibited by chilling temperatures in 35 C-treated leaves than in untreated leaves. Further, pre-exposure of potato leaves to 35 degrees C markedly increased the amplitude and the rate of light-induced changes in leaf absorbance at 505 nm (indicative of xanthophyll cycle activity), suggesting the possibility that moderately elevated temperature increased the accessibility of violaxanthin to the membrane-located de-epoxidase. This was supported by the quantitative analysis of the xanthophyll-cycle pigments before and after the 35 degrees C treatment, showing light-independent accumulation of zeaxanthin during mild heat stress. Based on these results, we propose that the rapid adjustment of the heat resistance of PSII may involve a modification of the interaction between violaxanthin and the light-harvesting complexes of PSII. As a consequence, the thermoresistance of PSII could be enhanced either directly through a conformational change of PSII or indirectly via a carotenoid-dependent modulation of membrane lipid fluidity.
An experimental study has been conducted for determining the behaviour of heat pipes in thermal storage; with fluid experiencing a phase change inside the tank. Experiments were conducted under ...various conditions during the cooling cycle. Heat was transferred from the thermal storage container to an air stream at different inlet air states; temperature, humidity and varying velocity. The system provided continuous cooling for more than 8 hours, and characteristics of the system are discussed.
1 Bacteriology Division, Scientific Institute of Public Health, 14 Wytsman street, B-1050 Brussels, Belgium 2,4 Laboratory of Microbiology, Faculty of Sciences 2 and BCCM TM /LMG Bacteria Collection ...4 , Ghent University, K. L. Ledeganckstraat 35, B-9000 Ghent, Belgium 3 AFSSA, 31 Av. Tony Garnier, 69364 Lyon cedex 07, France
Correspondence Sophie Bertrand s.bertrand{at}iph.fgov.be
Received 29 April 2005
Accepted 3 August 2005
In the present study, three Listeria monocytogenes strains and one Listeria innocua strain out of a collection of 241 Listeria isolates from human and food-processing sources were found to display resistance to tetracycline (TC) due to the presence of the tet (M) gene. Through sequence analysis, it was shown that tet (M) genes in two of the isolates belong to sequence homology group (SHG) II, a group comprising chromosomally encoded tet (M) genes previously found in Staphylococcus aureus and in lactobacilli. The tet (M) genes of the two other L. monocytogenes strains were associated with a member of the Tn 916 Tn 1545 family of conjugative transposons and were closely related to SHG III, which harbours enterococcal tet (M) genes associated with Tn 916 . One of these transposon-containing strains was able to transfer the tet (M) gene to Enterococcus faecalis recipient strain JH2-2. Collectively, these sequence and conjugation data indicate that the acquisition of tet (M) by Listeria strains may be triggered by successive transfers between other Gram-positive organisms.
Abbreviations: MC, minocycline; TC, tetracycline.
The GenBank/EMBL/DDBJ accession numbers for the partial sequences of the tet (M) genes of four Listeria strains described in this study are AJ704565AJ704568.
Using affinity chromatography on lactose-agarose, five β-galactoside binding lectins of 14 to 20 kDa were detected in the rat small intestinal mucosa. The prominant proteins of 17 and 19 kDa were ...purified to homogeneity by 2D-electrophoresis. Direct N-terminal sequencing of the 17 kDa protein and intrachain sequencing of the 19 kDa protein produced sequences which are part of the N-terminal domain of the L-36/galectin-4. A rabbit polyclonal antibody was raised against the 19 kDa lectin, which specifically recognized the 17 and 19 kDa lectins and detected a related 36 kDa protein in human undifferentiated HT29 cells.
Barley leaves were exposed for several min to a white light of photon flux density 1000 μmol m
−2 s
−1 leading to a massive conversion of the xanthophyll violaxanthin to antheraxanthin and zeaxanthin ...in the absence of lipid peroxidation. Using electron spin resonance spectroscopy and different spin-labeled stearate probes, we observed that this light treatment noticeably decreased thylakoid membrane lipid fluidity. The light-induced membrane rigidification (i) was proportional to the amount of zeaxanthin present in the membranes, (ii) was blocked by dithiothreitol, a potent inhibitor of the violaxanthin de-epoxidase, (iii) was slowly reversible in the dark, (iv) was not observed in thylakoids of an
Arabidopsis mutant that has no xanthophyll cycle and (v) was accompanied by a substantial increase in the thermostability of the ionic permeability properties of the thylakoid membranes. The amount of xanthophyll-cycle pigments found in photosystem II was observed to significantly decrease after illumination. Photoacoustic and chlorophyll fluorometric analyses of the illuminated leaves revealed that strong illumination decreased the quantum yield of photosynthetic oxygen evolution and the pigment antenna size of photosystem II in green light (preferentially absorbed by carotenoids) but not in red light (absorbed by chlorophylls only). Taken together in the light of previous in vitro data on carotenoids incorporated into artificial membranes, our results indicate that the xanthophyll cycle could be an ‘emergency mechanism’ that rapidly provides thylakoid membrane lipids with rigidifying carotenoid molecules upon sudden increase in light intensity. The significance of this mechanism for the membrane function and adaptation to stressful light and temperature conditions is discussed.
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