Surface free energies of oral streptococci

Abstract The surface free energies ( γ _b) of a variety of oral streptococci were determined from contact angle measurements on bacterial deposits, using the concept of dispersion and polar components. At least four strains of each species were tested. Strains of Streptococcus mutans, S. sanguis and S. salivarius possessed relatively high surface free energies (103 ± 12 mJ · m⁻²) and at the species level no significant difference was found. In contrast, the strains of S. mitis had remarkably low surface free energies (45 ± 14 mJ · m⁻²). S. milleri appeared to be a heterogeneous species, showing surface free energies over a range of 32–119 mJ · m⁻². No significant differences were observed between laboratory strains and strains freshly isolated from the oral cavity.     

Endocytes and breakdown of ribonuclease oligomers by sinusoidal rat liver cells in vivo: II. Effect of charge

Experiments presented in this paper suggest that sinusoidal rat liver cells recognize basic on proteins and that this recognition results in endocytosis of the proteins. Evidence for involvement of basic groups was obtained in two ways.Firstly, we changedd the opsitively charged amino groups of the cross-linked ribonuclease molecules to neutral or negative by acetylation or succinylation, respectively. The modified proteins did not contain easily reducible disulfide bonds and they were not very sensitive to endoproteases, suggesting that they were not denatured by the acetylation procedures. Acetylation and succinylation reduced uptake of the injected cross-linked ribonuclease derivatives by liver and spleen and abolsihed their rapid clearance from plasma. In nephrectomized rats about 75% of the polymer, 36% of the acetylated polumer and 32% of the succinylated polumer were endocytosed by liver after 6 h. For the dimer fraction these values were 59%, 23% and 27%, respectively. Autoradiography and subcellular fractionation of liver 30 min post-injection localized the acetylated polumer in the lysosomal/microsomal fraction of sinusoidal liver cessls, probably endothelial cells.Secondly, a positive correlation was found between binding of a number of ribonuclease derivatives of the cation exchanges SP-Sephadex G-25 and the rate of endocytosis by sinusoidal liver cells.     

Neonates know better than their mothers when selecting a host plant

Evolutionary ecological theory predicts that among insect herbivores ‘mothers know best’ when selecting a plant to deposit their eggs. Host‐plant selection is usually studied for the adult stage exclusively, although mothers have not always been reported to know best. Here, we investigate the host‐plant selection behaviour of caterpillars, which are considered to be completely dependent on their mothers’ choices. We use a system that offers a biologically relevant framework to compare the degree of participation of adults and juveniles in host‐plant selection. Our results show that neonate Pieris brassicae caterpillars can actively discriminate between conspecific Brassica oleracea plants with or without aphid (Brevicoryne brassicae) infestation. The caterpillars prefer aphid‐infested plants on which their performance is significantly better, while their mothers, the female butterflies, did not discriminate. We compared caterpillar preferences of individuals released individually or in groups, because P. brassicae is a gregarious species. We found that the strength of the preference for aphid‐infested plants was not affected by the degree of grouping. Caterpillar choices were made before contact with the plants, indicating that plant odours were used for orientation. However, the composition of the volatile blends emitted by plants with and without aphids did not show strong differences. Similarly, like with aphid‐infested plants, plants treated with salicylic acid (SA) were also preferred by neonates over untreated control, indicating that the infestation by aphids may have rendered the plants more attractive to the neonates via changes related to interference with JA‐signaling. The main parasitoid of the caterpillars did not discriminate between plants with hosts in the presence or absence of aphids, showing that top–down forces do not influence the relative suitability of the different food sources for the caterpillars. These data are discussed in the context of mothers and offspring having both important, but different roles in the process of host‐plant selection. Butterflies may select the plant species patch, while their offspring adjust and/or update the choices of their mothers at the local scale, within the micro‐habitat selected by the adult.     

A novel functional assay for fungal histidine kinases group III reveals the role of HAMP domains for fungicide sensitivity

Signal transduction systems comprising histidine kinases are suggested as new molecular targets of antibiotics. The important human fungal pathogen Candida albicans possesses three histidine kinases, one of which is the type III histidine kinase CaNik1, which activates the MAP kinase Hog1. We established a screening system for inhibitors of this class of histidine kinases by functional expression of the CaNIK1 gene in S. cerevisiae. This transformant was susceptible to fungicides to which the wild type strain was resistant, such as fludioxonil and ambruticin. Growth inhibition correlated with phosphorylation of Hog1 and was dependent on an intact Hog1 pathway. At the N-terminus the histidine kinase CaNik1 has four amino acid repeats of 92 amino acids each and one truncated repeat of 72 amino acids. Within these repeats we identified 9 HAMP domains with a paired structure. We constructed mutants in which one or two pairs of these domains were deleted. S. cerevisiae transformants expressing the full-length CaNIK1 showed the highest sensitivity to the fungicides, any truncation reduced the susceptibility of the transformants to the fungicides. This indicates that the HAMP domains are decisive for the mode of action of the antifungal compounds.     

Preparation and characterization of a stratum corneum substitute for in vitro percutaneous penetration studies

The intercellular stratum corneum (SC) lipids form the main barrier for diffusion of substances through the skin. A porous substrate covered with synthetic SC lipids would be an attractive model to study percutaneous penetration, hereby replacing native human SC. Prerequisite is that this stratum corneum substitute (SCS) is prepared with a uniform lipid composition and layer thickness. Furthermore, the lipid organization and orientation should resemble that in SC. The objective of this study was to investigate the utility of an airbrush spraying device to prepare a SCS composed of cholesterol, ceramides and free fatty acids on a polycarbonate filter. The results demonstrate that a proper choice of solvent mixture and lipid concentration is crucial to achieve a uniform distribution of the applied lipids over the filter surface. A smooth and tightly packed lipid layer is only obtained when the equilibration conditions are appropriately chosen. The SCS possesses two crystalline lamellar phases with periodicities similar to those present in native SC. The orientation of these lamellae is mainly parallel to the surface of the polycarbonate filter, which resembles the orientation of the intercellular SC lipids. In conclusion, the airbrush technique enables generation of a homogeneous SCS, which ultimately may function as a predictive in vitro percutaneous penetration model.     

Structure of the type III secretion recognition protein YscU from Yersinia enterocolitica

The inner-membrane protein YscU has an important role during the assembly of the Yersinia enterocolitica type III secretion injectisome. Its cytoplasmic domain (YscU^C) recognizes translocators as individual substrates in the export hierarchy. Activation of YscU entails autocleavage at a conserved NPTH motif. Modification of this motif markedly changes the properties of YscU, including translocator export cessation and production of longer injectisome needles. We determined the crystal structures of the uncleaved variants N263A and N263D of YscU^C at 2.05 Å and 1.55 Å resolution, respectively. The globular domain is found to consist of a central, mixed β-sheet surrounded by α-helices. The NPTH motif forms a type II β-turn connecting two β-strands. NMR analysis of cleaved and uncleaved YscU^C indicates that the global structure of the protein is retained in cleaved YscU^C. The structure of YscU^C variant N263D reveals that wild type YscU^C is poised for cleavage due to an optimal reaction geometry for nucleophilic attack of the scissile bond by the side chain of Asn263. In vivo analysis of N263Q and H266A/R314A YscU variants showed a phenotype that combines the absence of translocator secretion with normal needle-length control. Comparing the structure of YscU to those of related proteins reveals that the linker domain between the N-terminal transmembrane domain and the autocleavage domain can switch from an extended to a largely α-helical conformation, allowing for optimal positioning of the autocleavage domain during injectisome assembly.     

Dissociative Symptoms and Reported Trauma Among Patients with Spirit Possession and Matched Healthy Controls in Uganda

Spirit possession is a common, worldwide phenomenon with dissociative features. Studies in Europe and the United States have revealed associations among psychoform and somatoform dissociation and (reported) potential traumatic events. The aim of this study was to explore the relationships among spirit possession, dissociative symptoms and reported potentially traumatizing events in Uganda. One hundred nineteen persons with spirit possession, diagnosed by traditional healers, were compared to a matched control group of 71 nonpossessed persons. Assessments included demographic items and measures of dissociation and potentially traumatizing events. Compared to the nonpossessed group, the possessed group reported more severe psychoform dissociation and somatoform dissociation and more potentially traumatizing events. The associations between these events and both types of dissociation were significant. Yet, consistent with the cultural perception of dissociative symptoms, the participants subjectively did not associate dissociative symptoms with potentially traumatizing events. In conclusion, spirit possession deserves more interest as a possible idiom of distress and a culture-specific expression of dissociation related to potential traumatizing events.