Range‐wide population structure of European sea bass Dicentrarchus labrax

The euryhaline European sea bass Dicentrarchus labrax L., inhabiting the coasts of the eastern Atlantic Ocean and Mediterranean Sea, has had many opportunities for differentiation throughout its large natural range. However, evidence for this has been incompletely documented geographically and with an insufficient number of markers. Therefore, its full range was sampled at 22 sites and individuals were genotyped with a suite of mapped markers, including 14 microsatellite loci (N = 536) and 46 neutral or gene‐linked single nucleotide polymorphisms (SNPs; N = 644). We confirm that the Atlantic and Mediterranean basins harbour two distinct lineages. Within the Atlantic Ocean no pattern was obvious based on the microsatellite and SNP genotypes, except for a subtle difference between South‐eastern and North‐eastern Atlantic sea bass attributed to limited introgression of alleles of Mediterranean origin. SNP genotypes of the Mediterranean lineage differentiated into three groups, probably under the influence of geographical isolation. The Western Mediterranean group showed genetic homogeneity without evidence for outlier loci. The Adriatic group appeared as a distinct unit. The Eastern Mediterranean group showed a longitudinal gradient of genotypes and most interestingly an outlier locus linked to the somatolactin gene. Overall, the spatial pattern fits those observed with other taxa of between‐basin segregation and within‐basin connectivity, which concurs well with the swimming capabilities of European sea bass. Evidence from a few outlier loci in this and other studies encourages further exploration of its regional connectivity and adaptive evolution.     

Mitogen-activated protein kinase-defective Candida albicans is avirulent in a novel model of localized murine candidiasis

Candida albicans strains with a deletion of the mitogen-activated protein kinase CEK1 gene are defective in the yeast to hyphal transition on solid surfaces in vitro. The virulence of a cek1Δ/cek1Δ null mutant strain was compared with its wild-type parent strain (WT) in a novel model of localized candidiasis. The mammary glands of lactating mice (at day 5 postpartum) were infected for 2, 4 and 6 days with 50 μl suspension containing 1×10⁵, 1×10⁶ and 1×10⁷ blastospores before death. Infected and non-infected control glands were evaluated pathologically. All animals infected with cek1Δ/cek1Δ null mutant strains showed no lesions while 65% of animals infected with the WT strain had severe lesions characterized by widespread heterophilic infiltration, necrosis, and abscess formation. As an additional control, animals infected with the disrupted strain complemented with the WT CEK1, on a replicating plasmid, also showed severe pathological changes similar to the WT strain. These results clearly demonstrate that the CEK1 gene codes for a virulence determinant of C. albicans and that the mouse mastitis model is well suited for the discriminative study of the pathogenicity of different C. albicans strains.     

Molecular cloning and analysis of genes for production of K5, K7, K12, and K92 capsular polysaccharides in Escherichia coli.

With a DNA fragment from within the region encoding the transport functions for K1 production as a hybridization probe in Southern blot experiments, homologous DNA sequences were detected in the DNA from Escherichia coli strains producing K5, K7, K92, and K100 capsular polysaccharides. No homology with the laboratory strain LE392 was detected. The same DNA probe was used to prescreen cosmid libraries in LE392 by colony hybridization, as a rapid method to isolate clones encoding the genes for K5, K7, K12, and K92 antigen production. Clones carrying sequences homologous to the probe that also produced capsular material were identified by using polyclonal and monoclonal antibodies raised against the K antigen in question and K antigen-specific phages. By restriction enzyme mapping of the appropriate cosmid clones it was possible to align the genes for the production of different K antigens in terms of common restriction endonuclease cleavage sites. A DNA fragment encoding the postulated transport functions for K7 antigen production could complement deletion mutations in the transport functions for K1 antigen production. Thus the transport to the cell surface of chemically distinct polysaccharides may be by a common process. Analysis in E. coli of the proteins produced by plasmids carrying the likely transport functions for K1, K5, and K7 antigen production revealed that each region coded for a similar polypeptide.     

Lipopolysaccharides of Pseudomonas spp. that stimulate plant growth: composition and use for strain identification.

The outer membrane proteins of a series of fluorescent, root-colonizing, plant-growth-stimulating Pseudomonas spp. having been characterized (L. A. de Weger et al., J. Bacteriol. 165:585-594, 1986), the lipopolysaccharides (LPSs) of these strains were examined. The chemical composition of the LPSs of the three best-studied plant-growth-stimulating Pseudomonas strains WCS358, WCS361, and WCS374 and of P. aeruginosa PAO1 as a reference strain was determined and appeared to differ from strain to strain. The 2,6-dideoxy-2-aminosugar quinovasamine was the most abundant compound in the LPS of strain WCS358. Analysis by sodium dodecyl sulfate-polyacrylamide gel electrophoresis of purified LPS and of proteinase K-treated cell envelopes revealed ladderlike patterns for most of these strains. These patterns were not substantially influenced by differences in culture conditions. Analysis of proteinase K-treated cell envelopes of 24 root-colonizing Pseudomonas spp. revealed a unique band pattern for each strain, suggesting a great variety in the LPS structures present in these root colonizers. Therefore, electrophoretic analysis of LPS can be used for characterization and identification of the fluorescent root-colonizing Pseudomonas strains.     

Structural studies of an emulsion-stabilizing exopolysaccharide produced by an adhesive, hydrophobic Rhodococcus strain.

The primary structure of an emulsion-stabilizing exopolysaccharide from the adhesive, hydrophobic Rhodococcus strain No. 33 was elucidated by NMR spectroscopy, methylation analyses, periodate oxidation and oligosaccharide analyses. The polysaccharide PS-33 consisted of rhamnose, galactose, glucose and glucuronic acid in molar ratios of 2:1:1:1. The main chain contained 3-substituted alpha-D-glucuronic acid linked to the 3-position at alpha-L-rhamnose, in addition to 3-substituted residues of beta-D-galactose and alpha-D-glucose. The alpha-L-rhamnose of the side chain was linked to position 4 of the galactose. In addition, the polysaccharide was O-acetylated, corresponding to one acetyl group per repeating unit. From the results two structural possibilities could be suggested. As the polysaccharide carries hydrophobic groups (methyl of rhamnose/O-acetyl), it is very likely that these are of general significance for the emulsifying activity of polysaccharides. It also seems to be possible that this polysaccharide is at least partially responsible for the hydrophobic cell surface properties of the Rhodococcus strain No. 33 and it may be involved in hydrophobic interactions when adhering to hydrophobic interfaces.     

ORGANIC MERCURIAL ENCEPHALOPATHY: IN VIVO AND IN VITRO EFFECTS OF METHYL MERCURY ON SYNAPTOSOMAL RESPIRATION

—A reproducible model of subacute methyl mercury (MeHg) intoxication was developed in the adult rat following the daily intragastric administration of 10 mg methyl mercury/kg body wt. Synaptosomes isolated from animals during the latent phase of mercury neurotoxicity (6-10 days) demonstrated no significant change in respiratory control, State 3, State 4, or 2,4-dinitrophenol stimulated respiration with succinate, glutamate or pyruvate plus malate. During the neurotoxic phase, a significant decline in respiratory control was evident with all substrates. Cerebellar synaptosomes revealed qualitatively similar but quantitatively greater inhibition of 2,4-dinitrophenol stimulated respiration during the latent and neurotoxic phases with glutamate. In vitro studies of synaptosome respiration, oxidative phosphorylation and respiratory control with 5-15 μm -methyl mercury revealed a stimulation of initial State 4 respiration, loss of RCI, inhibition of State 3 but no change in the gramicidin or 2,4-dinitrophenol uncoupled rate supported by pyruvate-malate. Phosphate did not relieve the State 3 inhibition. At 25 μm -methyl mercury and above, considerable inhibition of electron transfer occurred. At this concentration, cytochrome c oxidase was inhibited 50%. Isosmotic replacement of medium KC1 by mannitol reduced the MeHg stimulation of State 4 respiration but had no effect on MeHg inhibition of ADP stimulated respiration. Half-maximal stimulation of State 4 respiration by MeHg occurred at [K]⁺⋍ 6 mm . These findings are compatible with an energy-linked methyl mercury induced cation translocation across the synaptosome (mitochondrial) membrane.     

On the effect of rfe mutation on the biosynthesis of the 08 and 09 antigens of E. coli.

From phosphomannose isomerase-less mutants of $\text{E. coli}$ strains 08 and 09, $\text{rfe}{}^{\mathrm{?}}$ derivatives were constructed by recombination with a $\text{Salmonella rfe}{}^{\mathrm{?}}$ donor. In contrast to membranes from the parent $\text{E. coli}$ strains, those from the $\text{rfe}{}^{\mathrm{?}}$ recombinants did not synthesize the 08 or 09 mannan from GDP mannose $\text{in vitro}$. They could, however, be restored to biosynthetic activity with butanol extracts from the $\text{E. coli rfe}{}^{\mathrm{+}}$ bacteria. This indicated that the $\text{rfe}$ mutation affects the synthesis of a hydrophobic acceptor.