A Highly Arginolytic Streptococcus Species That Potently Antagonizes Streptococcus mutans

The ability of certain oral biofilm bacteria to moderate pH through arginine metabolism by the arginine deiminase system (ADS) is a deterrent to the development of dental caries. Here, we characterize a novel Streptococcus strain, designated strain A12, isolated from supragingival dental plaque of a caries-free individual. A12 not only expressed the ADS pathway at high levels under a variety of conditions but also effectively inhibited growth and two intercellular signaling pathways of the dental caries pathogen Streptococcus mutans. A12 produced copious amounts of H₂O₂ via the pyruvate oxidase enzyme that were sufficient to arrest the growth of S. mutans. A12 also produced a protease similar to challisin (Sgc) of Streptococcus gordonii that was able to block the competence-stimulating peptide (CSP)–ComDE signaling system, which is essential for bacteriocin production by S. mutans. Wild-type A12, but not an sgc mutant derivative, could protect the sensitive indicator strain Streptococcus sanguinis SK150 from killing by the bacteriocins of S. mutans. A12, but not S. gordonii, could also block the XIP (comX-inducing peptide) signaling pathway, which is the proximal regulator of genetic competence in S. mutans, but Sgc was not required for this activity. The complete genome sequence of A12 was determined, and phylogenomic analyses compared A12 to streptococcal reference genomes. A12 was most similar to Streptococcus australis and Streptococcus parasanguinis but sufficiently different that it may represent a new species. A12-like organisms may play crucial roles in the promotion of stable, health-associated oral biofilm communities by moderating plaque pH and interfering with the growth and virulence of caries pathogens.     

Human epidermis reconstructed in vitro: A model to study keratinocyte differentiation and its modulation by retinoic acid

Summary It was possible to reconstruct epidermis in vitro by seeding dissociated keratinocytes on de-epidermized dermis and growing such recombined cultures for 1 wk, exposed to air, at the surface of the culture medium. These conditions were chosen to mimic the transdermal feeding and the exposure to the atmosphere that occur in vivo. Contrary to classical cultures performed on plastic dishes covered with culture medium, which show rudimentary differentiation and organization, the architecture of the stratified epithelium obtained in reconstructed cultures and the distribution of differentiation markers such as suprabasal keratins, involucrin, and membrane-bound transglutaminase were similar to those of the epidermis of skin biopsies; moreover, biochemical studies showed that the synthesis of the various keratins and the production of cornified envelopes was similar to what is found with skin specimens. The reconstructed epidermis model was found to be very useful to study in vitro the effect of retinoic acid on keratinocyte differentiation and epidermal morphogenesis.     

Relations between fluorescence and thylakoid structure in Porphyridium cruentum

The increase in chlorophyll a steady-state fluorescence, induced by high NaCl concentration in Porphyridium cruentum in the presence of 3-(3,4-dichlorophenyl)-1,1-dimethylurea, is directly correlated with a significant decrease in thylakoid thickness. It does not appear affected either by alteration of light absorption due to configurational change or by electron transport processes. Oxygen evolution occurs only in intact structures. The interrelationship between membrane structure, oxygen evolution and chlorophyll a steady-state fluorescence is discussed.     

The mode of nuclear DNA synthesis in experimentally induced binucleate cells of root meristems

The synthesis of DNA does not proceed in a perfectly synchronous way in about 20% of the binucleate cells induced in Allium sativum L. root meristems by treatment with methyl 3 hydroxy 6 (1 H, 3 H) quinazoline dione, 2.4 (an inhibitor of cytokinesis). — Nuclear labelling after tritiated thymidine incorporation and the measurement of nuclear DNA by cytophotometry both establish that the beginning of the S phase as well as its duration may be different in the two nuclei included in a single cytoplasm. Yet the nuclear synchronism progressively asserts itself as the cell cycle goes on and, following this asynchronous synthesis, the beginning of mitosis is synchronous. The restoration of such a coordination points to the existence in the cytoplasm of separable factors inducing DNA synthesis and mitosis.     

Fixation of phycobiliproteins to photosynthetic membranes by glutaraldehyde

Summary Treatment of intact cells of two unicellular red algae (Porphyridium spp.) and of an unicellular blue-green alga (Gloeocapsa alpicola) with glutaraldehyde (3% v/v) has only a slight effect on the absorption spectra of their photopigment systems, but stabilizes the normally labile physical association between phycobili-proteins and the chlorophyll-bearing thylacoids. On subsequent breakage of such cells, a substantial fraction of the total phycobiliprotein (30–70%) sediments in a sucrose gradient, in association with the chlorophyll-containing membrane fragments, from which it cannot be dissociated by treatment with detergents.     

Reciprocal potentiation of the bronchoconstrictor activity of histamine and 5-hydroxytryptamine in the guinea pig

Bronchoconstriction due to aerosolized histamine (H), 5-hydroxytryptamine (5-HT) and combined administration of both substances has been studied on 53 guinea-pigs. The results are consistant with: a major bronchoconstrictor effect obtained with H than with 5-HT; a potentiation of the individual effects of H and 5-HT in two thirds of the guinea-pigs, by the combined administration of the two drugs simultaneously; a more potent antagonistic effect of Ketanserin against 5-HT than against H; potentiation due to the combined administration of 5-HT and H is suppressed by Ketanserin; neither vagal reflexes nor cholinergic receptors seem to interfere with the bronchospastic response of the guinea-pig to H and 5-HT.     

Calcium Spiking Patterns and the Role of the Calcium/Calmodulin-Dependent Kinase CCaMK in Lateral Root Base Nodulation of Sesbania rostrata

Nodulation factor (NF) signal transduction in the legume-rhizobium symbiosis involves calcium oscillations that are instrumental in eliciting nodulation. To date, Ca²⁺ spiking has been studied exclusively in the intracellular bacterial invasion of growing root hairs in zone I. This mechanism is not the only one by which rhizobia gain entry into their hosts; the tropical legume Sesbania rostrata can be invaded intercellularly by rhizobia at cracks caused by lateral root emergence, and this process is associated with cell death for formation of infection pockets. We show that epidermal cells at lateral root bases respond to NFs with Ca²⁺ oscillations that are faster and more symmetrical than those observed during root hair invasion. Enhanced jasmonic acid or reduced ethylene levels slowed down the Ca²⁺ spiking frequency and stimulated intracellular root hair invasion by rhizobia, but prevented nodule formation. Hence, intracellular invasion in root hairs is linked with a very specific Ca²⁺ signature. In parallel experiments, we found that knockdown of the calcium/calmodulin-dependent protein kinase gene of S. rostrata abolished nodule development but not the formation of infection pockets by intercellular invasion at lateral root bases, suggesting that the colonization of the outer cortex is independent of Ca²⁺ spiking decoding.