Nascent teichoic acids insertion into the cell wall directs the localization and activity of the major pneumococcal autolysin LytA.

The bacterial cell wall is in part composed of the peptidoglycan (PG) layer that maintains the cell shape and sustains the basic cellular processes of growth and division. The cell wall of Gram-positive bacteria also carries teichoic acids (TAs). In this work, we investigated how TAs contribute to the structuration of the PG network through the modulation of PG hydrolytic enzymes in the context of the Gram-positive Streptococcus pneumoniae bacterium. Pneumococcal TAs are decorated by phosphorylcholine residues which serve as anchors for the Choline-Binding Proteins, some of them acting as PG hydrolases, like the major autolysin LytA. Their binding is non covalent and reversible, a property that allows easy manipulation of the system. In this work, we show that the release of LytA occurs independently from its amidase activity. Furthermore, LytA fused to GFP was expressed in pneumococcal cells and showed different localization patterns according to the growth phase. Importantly, we demonstrate that TAs modulate the enzymatic activity of LytA since a low level of TAs present at the cell surface triggers LytA sensitivity in growing pneumococcal cells. We previously developed a method to label nascent TAs in live cells revealing that the insertion of TAs into the cell wall occurs at the mid-cell. In conclusion, we demonstrate that nascent TAs inserted in the cell wall at the division site are the specific receptors of LytA, tuning in this way the positioning of LytA at the appropriate place at the cell surface.

Exploring the relationship between demographic and disease-related variables and perceived effect of health status on sexual activity in patients with axial spondyloarthritis: associations found only with non-disease variables.

OBJECTIVE: To explore the relationship between demographic and disease-related variables and the perceived effect of health status on sexual activity in patients with axial spondyloarthritis (ax-SpA). METHOD: The study assessed 379 ax-SpA patients consecutively recruited from two rheumatology outpatient clinics. Data collection included information on demographics, markers and measures of ax-SpA disease, treatment, comorbidity, and health-related quality of life (HRQoL) using the Short Form-36. The perceived effect of health status on sexual activity was assessed using question 15 in the HRQoL instrument 15D. RESULTS: The mean age of the patients was 45.6 years, 66.5% were men, 87.3% were human leucocyte antigen-B27 positive, and mean disease duration was 13.9 years. A total of 312 patients (82.3%) reported their health status to have no/little effect and 17.7% patients reported their health status to have a large negative effect on their sexual activity. In univariate analysis, increased body mass index (BMI), smoking, alcohol consumption, unemployed status, low physical activity, comorbidities, and higher disease activity (Bath Ankylosing Spondylitis Questionnaire), impaired body movement and lower HRQoL were associated with a large effect on sexual activity. In adjusted analyses, only female gender, high BMI, current smoking, and low HRQoL showed significant associations. CONCLUSION: Approximately 20% of ax-SpA patients reported a large negative effect on their sexual activity. Female gender, high BMI, current smoking, and reduced HRQoL were associated with health status having a large effect on sexual activity, whereas no measures reflecting ax-SpA disease showed an independent association.

The reduction of nitrous oxide to dinitrogen by Escherichia coli.

Escherichia coli K12 reduces nitrous oxide stoichiometrically to molecular nitrogen with rates of 1.9 mumol/h x mg protein. The activity is induced by anaerobiosis and nitrate. N2-formation from N2O is inhibited by C2H2 (Ki approximately 0.03 mM in the medium) and nitrite (Ki = 0.3 mM) but not by azide. A mutant defective in FNR synthesis is unable to reduce N2O to N2. The reaction in the wild type could routinely be followed by gas chromatography and alternatively by mass spectrometry measuring the formation of 15N2 from 15N2O. The enzyme catalyzing N2O-reduction in E. coli could not be identified; it is probably neither nitrate reductase nor nitrogenase. E. coli does not grow with N2O as sole respiratory electron acceptor. N2O-reduction might not have a physiological role in E. coli, and the enzyme involved might catalyze something else in nature, as it has a low affinity for the substrate N2O (apparent Km approximately 3.0 mM). The capability for N2O-reduction to N2 is not restricted to E. coli but is also demonstrable in Yersinia kristensenii and Buttiauxella agrestis of the Enterobacteriaceae. E. coli is able to produce NO and N2O from nitrite by nitrate reductase, depending on the assay conditions. In such experiments NO2- is not reduced to N2 because of the high demand for N2O of N2O-reduction and the inhibitory effect of NO2- on this reaction.

Structural organization of the chloroplast genome of the chromophytic alga Vaucheria bursata.

The chloroplast genome of the chromophytic alga Vaucheria bursata has been characterized by restriction site and gene mapping analysis. It is represented by a circular molecule 124.6 kb in size. An inverted sequence duplication (IR) not larger than 5.85 kb carries the rRNA genes and separates two single-copy regions of 64.6 kb and 48.3 kb from one another. The Vaucheria plastid genome exists in two equimolar isomers which is due to intramolecular flip-flop recombination within the IR sequences. The coding sites for 21 structural and soluble proteins have been mapped on both single-copy regions using heterologous gene sequences as probes. Although the overall gene order is found to be rearranged when compared with other chromophytic algal and land plant chloroplast genomes, most of the transcriptional units of cyanobacteria and land plant chloroplast genomes appear to be conserved. The phylogenetic implications of these findings are further discussed.

Structural organization and evolution of the plastid genome of Vaucheria sessilis (Xanthophyceae).

The plastid DNAs of 18 Vaucheria sessilis strains from various habitats in western Europe were digested with the restriction endonucleases Eco RI, Sal I, Bam HI and Pvu II. Their restriction patterns showed variable fragment divergencies. Two main groups of plastid genomes were recognized, which were substantiated by morphological features. The differences among the restriction patterns could be attributed to the loss or appearance of restriction sites and to minor size variations caused by deletions/insertions. The Sal I and Bam HI restriction sites which together discriminate six different plastid genomes were mapped on the circular molecule of 124 kilobase paris (kbp). The plastid genomes of several Vaucheria sessilis strains were shown to exist in two inversion isomers caused by intramolecular recombination within the inverted repeat segments.