Molecular characterization of the clumping factor (fibrinogen receptor) of Staphylococcus aureus

Four mutants of Staphylococcus aureus strain Newman that were defective in the fibrinogen receptor (clumping factor) were isolated by transposon Tn917 mutagenesis. Southern hybridization analysis of the mutants identified transposon-host DNA junction fragments, one of which was cloned and used to generate a probe to identify and clone the wild-type clumping factor locus (clfA). The mutants failed to form clumps in soluble fibrinogen and adhered poorly to polymethylmethacrylate (PMMA) coverslips coated with fibrinogen. A single copy of the clfA gene, when introduced into the chromosome of the mutant strains, fuily compiemented the ciumping deficiency of these strains and restored the ability of these mutants to adhere to fibrinogen-coated PMMA. in addition, the cloned clfA gene on a shuttle plasmid aiiowed the weakiy ciumping strain 8325-4 to form clumps with the same avidity as the wild-type strain Newman and also significantly enhanced the adherence of 8325-4 strains. Thus the formation of clumps in soluble fibrinogen correlated with adherence of bacteria to solid-phase fibrinogen. The clfA gene encodes a fibrinogen-binding protein with an apparent molecular mass of c. 130 kDa. The amino acid sequence of the protein was deduced from the DNA sequence; it was predicted that a 896 residue protein (molecular mass 92 kDa) would be expressed. The putative ClfA protein has features that suggest that it is associated with the ceil surface. Furthermore it contains a novel 308 residue region comprising dipeptide repeats predominantly of Asp and Ser ending 28 residues upstream from the LPXTG motif common to wall-associated proteins. Significant homology was found between the ClfA protein and the fibronectin-binding proteins of S. S. aureus, particularly in the N-and C-termini.     

Growth and reproduction of an estuarine population of the colonial hydroidCordylophora caspia (Pallas) in the northern Baltic Sea

Growth and reproduction of the colonial hydroidCordylophora caspia were monitored during the breeding season in natural conditions. In 1987, a life history study was carried out on the upright stems of the main stolon. Mean size of uprights varied cyclically. The first peak coincided with the peak number of sexual hydranths, after which the mean upright length decreased, possibly indicating somatic costs of sexual reproduction. Extrinsic factors like flooding may also have contributed to cyclical changes in upright size. In 1988 and 1989, colonies were reared on experimental plates in the estuary. In 1988, colonies grew until mid July, after which they regressed to a dormant condition and then started growing again in mid August. Predation and space competition are discussed as possible causes for this dormancy in the middle of the growing season. In 1989, colonies grew continually, with the exception of a decline in colony biomass and number of feeding hydranths at the end of July, just following the peak of sexual reproduction. Sexual reproduction started in the early stages of colonial development for all years. During early summer,C. caspia allocated resources simultaneously in colonial growth and sexual reproduction. However, sexual reproduction had a clear peak in mid summer, and thereafter sexual reproduction ceased while colonial growth continued.     

REPRODUCTION AND RECRUITMENT OF NUCULOMA TENUIS (BIVALVIA: NUCULOIDA) FROM LOCH ETIVE, SCOTLAND

A population of the protobranch bivalve Nuculoma tenuis at adepth of c. 54 m in Loch Etive, West Scotland, was sampled monthlyfrom September 1986 to October 1988. The density of N. tenuisin the samples, and the relative proportions of adults and postlarvae,varied markedly from month to month suggesting patchiness atthe scale of the sampling. There was evidence for spatial segregationof adults and postlarvae. A seasonal reproductive cycle occurred,with a synchronised spawnout in winter; the exact timing appearingto vary in successive years by up to 2 months. Despite markedlyseasonal spawning, no recruitment peak was evident in shell-lengthfrequencies, and benthic postlarvae were present throughoutthe year. This corroborates findings from an earlier laboratorystudy, suggesting a prolonged phase of meiobenthic developmentin this species. (Received 1 February 1995; accepted 15 March 1995)     

Evidence for K+ channel control in Vicia guard cells coupled by G-proteins to a 7TMS receptor mimetic

To explore the involvement of a class of seven-trans-membrane-span (7TMS) receptors in cellular signalling, a synthetic analogue (mas7) of the amphipathic tetradecapeptide mastoparan was used to mimic hormonal stimulus in guard cells of Vicia faba. The ability for mas7 to substitute for an activated receptor complex was assayed by the effect on guard cell ion channel activities in the absence of any hormonal stimulus. Currents carried by inward-(I_K,in) and outward-(I_K,out) rectifying potassium channels were determined under voltage clamp conditions before, during, and after exposure to mas7. The dominant effect of mas7 was to inactivate I_K,in within 30 sec of application. By contrast, I_K,out was largely unaffected under these conditions. The effect of mas7 on I_K,in was both concentration- and voltage-dependent. At any one clamp voltage, mas7 inactivation showed Michaelian behaviour, with a mean K_i of 0.05 ± 0.02 µM at ?240 mV. Increasing mas7 concentration also shifted the voltage for half-maximal activation of the current negative, with 0.5 µM mas7 effecting a ?13 ± 2 mV displacement and lengthening the halftime for activation of the current by up to threefold. By contrast, the non-amphipathic analogue of mas7, masCP, had no appreciable effect on the steady-state current or its activation kinetics; nor was the poly-cation polylysine able to substitute for mas7 in its action on the K⁺ channels. Application of the non-hydrolysable analogue of GDP, GDP-β-S, either by iontophoresis or by diffusion from the microelectrode, effectively blocked mas7-induced inactivation of I_K,in. These, and additional results provide in vivo evidence for the involvement of G-protein-linked 7TMS receptors in the regulation of membrane transport in a higher plant cell.