Steroid structural requirements for interaction of ostreolysin, a lipid-raft binding cytolysin, with lipid monolayers and bilayers

Ostreolysin, a cytolytic protein from the edible oyster mushroom (Pleurotus ostreatus), recognizes and binds specifically to membrane domains enriched in cholesterol and sphingomyelin (or saturated phosphatidylcholine). These events, leading to permeabilization of the membrane, suggest that a cholesterol-rich liquid-ordered membrane phase, which is characteristic of lipid rafts, could be its possible binding site. In this work, we present effects of ostreolysin on membranes containing various steroids. Binding and membrane permeabilizing activity of ostreolysin was studied using lipid mono- and bilayers composed of sphingomyelin combined, in a 1/1 molar ratio, with natural and synthetic steroids (cholesterol, ergosterol, β-sitosterol, stigmasterol, lanosterol, 7-dehydrocholesterol, cholesteryl acetate, and 5-cholesten-3-one). Binding to membranes and lytic activity of the protein are both shown to be dependent on the intact sterol 3β-OH group, and are decreased by introducing additional double bonds and methylation of the steroid skeleton or C17-isooctyl chain. The activity of ostreolysin mainly correlates with the ability of the steroids to promote formation of liquid-ordered membrane domains, and is the highest with cholesterol-containing membranes. Furthermore, increasing the cholesterol concentration enhanced ostreolysin binding in a highly cooperative manner, suggesting that the membrane lateral distribution and accessibility of the sterols are crucial for the activity of this new member of cholesterol-dependent cytolysins.     

Cellulosomics, a gene-centric approach to investigating the intraspecific diversity and adaptation of Ruminococcus flavefaciens within the rumen

Background

The bovine rumen maintains a diverse microbial community that serves to break down indigestible plant substrates. However, those bacteria specifically adapted to degrade cellulose, the major structural component of plant biomass, represent a fraction of the rumen microbiome. Previously, we proposed scaC as a candidate for phylotyping Ruminococcus flavefaciens, one of three major cellulolytic bacterial species isolated from the rumen. In the present report we examine the dynamics and diversity of scaC-types both within and between cattle temporally, following a dietary switch from corn-silage to grass-legume hay. These results were placed in the context of the overall bacterial population dynamics measured using the 16S rRNA.

Principal Findings

As many as 117 scaC-types were estimated, although just nineteen were detected in each of three rumens tested, and these collectively accounted for the majority of all types present. Variation in scaC populations was observed between cattle, between planktonic and fiber-associated fractions and temporally over the six-week survey, and appeared related to scaC phylogeny. However, by the sixth week no significant separation of scaC populations was seen between animals, suggesting enrichment of a constrained set of scaC-types. Comparing the amino-acid translation of each scaC-type revealed sequence variation within part of the predicted dockerin module but strong conservation in the N-terminus, where the cohesin module is located.

Conclusions

The R. flavefaciens species comprises a multiplicity of scaC-types in-vivo. Enrichment of particular scaC-types temporally, following a dietary switch, and between fractions along with the phylogenetic congruence suggests that functional differences exist between types. Observed differences in dockerin modules suggest at least part of the functional heterogeneity may be conferred by scaC. The polymorphic nature of scaC enables the relative distribution of R. flavefaciens strains to be examined and represents a gene-centric approach to investigating the intraspecific adaptation of an important specialist population.     

Soil chemical properties affect the concentration of elements (N,P, K,Ca, Mg,As, Cd,Cr, Cu,Fe, Mn,Ni, Pb,and Zn) and their distribution between organs of Rumex obtusifolius

Background and aims

The ionome (elemental composition) of grassland species has rarely been studied at the level of individual organs and little is known about effects of soil chemical properties on the ionome. Using the model oxalate plant Rumex obtusifolius, we asked how its biomass production and the distribution of elements between its organs is affected by soil chemical properties.

Methods

We established a pot experiment with R. obtusifolius planted in acidic non-contaminated control and in slightly acidic and alkaline soils anthropogenically contaminated by the risk elements As, Cd, Pb, and Zn. Both contaminated soils were untreated and treated by lime and superphosphate. We determined biomass production and the concentrations of elements in its organs.

Results

Biomass production was negatively related to the mobility of micro- and risk elements. Restricted transport of micro- and risk elements from belowground organs into leaves was recorded in untreated contaminated soils. In both lime-treated soils and in superphosphate-treated alkaline soil, elevated transport of micro- and risk elements from belowground organs into leaves was recorded in comparison to untreated contaminated soils. The lowest concentrations of micro- and risk elements were recorded in stems and seeds, followed by belowground organs and leaves.

Conclusions

R. obtusifolius is an As-, Cd-, Pb-, and Zn-excluder and is sensitive to high availability of micro- and risk elements in the soil. Soil chemical properties affect the distribution of essential elements within the plant greatly.     

Julius Sachs (1832–1897) and the Unity of Life

In 1865, the German botanist Julius Sachs published a seminal monograph entitled Experimental-Physiologie der Pflanzen (Experimental Physiology of Plants) and hence became the founder of a new scientific discipline that originated 150 y ago. Here, we outline the significance of the achievements of Sachs. In addition, we document, with reference to his Vorlesungen über Pflanzen-Physiologie (Lectures on the Physiology of Plants, 1882), that Sachs was one of the first experimentalists who proposed the functional unity of all organisms alive today (humans, animals, plants and other “vegetable” organisms, such as algae, cyanophyceae, fungi, myxomycetes, and bacteria).     

On the Evolutionary Relationship in the Family Brassicaceae

• 1 The study gives the evaluation of the dissepimentum and gynophore for the establishment of the evolutionary relationship in the family Brassicaceae.

• 2 The genus Macropodium R. Br. represents an organizational degree. Different, divergently going younger evolutionary lines, developed from evolutionary lines leading to both present species.

     

On signals of phase transitions in salmon population dynamics

Critical slowing down (CSD) reflects the decline in resilience of equilibria near a bifurcation and may reveal early warning signals (EWS) of ecological phase transitions. We studied CSD in the recruitment dynamics of 120 stocks of three Pacific salmon (Oncorhynchus spp.) species in relation to critical transitions in fishery models. Pink salmon (Oncorhynchus gorbuscha) exhibited increased variability and autocorrelation in populations that had a growth parameter, r, close to zero, consistent with EWS of extinction. However, models and data for sockeye salmon (Oncorhynchus nerka) indicate that portfolio effects from heterogeneity in age-at-maturity may obscure EWS. Chum salmon (Oncorhynchus keta) show intermediate results. The data do not reveal EWS of Ricker-type bifurcations that cause oscillations and chaos at high r. These results not only provide empirical support for CSD in some ecological systems, but also indicate that portfolio effects of age structure may conceal EWS of some critical transitions.     

Revisiting santa rosalia to unfold a degeneracy of classic models of speciation

Abstract Many classic models of speciation incorporate assortative mating based on mating groups, such as plants with different flowering times, and they investigate whether an ecological trait under disruptive natural selection becomes genetically associated with the selectively neutral mating trait. It is well known that this genetic association is potently destroyed by recombination. In this note, we point out a more fundamental difficulty: if a "knife-edge" symmetry assumption of previous models is violated, then the mating trait is no longer neutral and sexual selection eliminates the polymorphism in the mating locus. This result strengthens the growing consensus that magic traits are the more likely route to nonallopatric speciation. We expand the model assuming also ecological selection on the mating trait and investigate the conditions for natural selection to overcome sexual selection and maintain mating polymorphism; we find that the combination of natural and sexual selection can cause also bistability of allele frequencies.     

Prevalence of the Helicobacter pylori babA2 gene and correlation with the degree of gastritis in infected Slovenian children

The aims of our study were to determine the prevalence of the babA2 gene within Helicobacter pylori strains circulating in the Slovenian pediatric population, to further clarify its significance in causing inflammation of gastric mucosa in children and to verify whether cagA, vacA, iceA and babA genes work independently or synergistically in causing gastritis. A total of 163 H. pylori isolates obtained from the same number of children were tested for the presence of cagA, vacA and iceA genes using previously established methods, while the babA2 gene was determined using novel polymerase chain reaction assay targeting a 139-bp fragment of the central region of babA2. The babA2 gene was detected in 47.9 % of H. pylori samples. The presence of the babA2 gene was strongly associated with cagA, vacA s1 and vacA m1 genotype. The babA2 status correlated positively with bacterial density score, activity of inflammation and chronic inflammation of gastric mucosa. No significant correlation was found between the babA2 status and the presence of atrophy or intestinal metaplasia. In addition, the activity of gastric inflammation and density score were significantly associated with the coexpression of the cagA, vacA s1, vacA m1 and babA2 genes. The study, which included the largest number of pediatric H. pylori samples to date, confirmed that babA2 gene plays an important role in the pathogenesis of H. pylori gastritis in children. Furthermore, our results suggest that babA2, cagA and vacA s1 and m1 gene products may work synergistically in worsening the inflammation of gastric mucosa.     

Role of UV-inducible proteins in repair of various wild-type Escherichia coli cells

3 wild-type strains of E. coli, namely K12 AB2497, B/r WP2 and 15 555-7v proficient in excision and post-replication repair, differ markedly in their UV resistance. To elucidate this difference, the influence was investigated of induction by application of inducing fluence (IF) before lethal fluence (LF) on repair processes after LF. In cells distinguished by low UV resistance (E. coli 15 555-7; E. coli B/r WP2), dimer excision was less complete in cultures irradiated with IF + LF than in cultures irradiated with LF only. The highly resistant E. coli K12 AB2497 performed complete excision both after IF + LF or after LF alone. All 3 types of cell survived better after IF + LF than after LF only. Because, in most strains so far investigated, the application of IF reduced dimer excision and increased survival, dimer excision per se does not appear important for survival.We conclude that the rate and completeness of dimer excision can serve as a measure of efficiency of the excision system whose action is necessary for repair of another lesion. Cells of all investigated strains could not resume DNA replication and died progressively when irradiated with LF and post-incubated with chloramphenicol (LF CAP⁺). Thus, it appears that inducible proteins are necessary for repair in all wild-type E. coli cells give with potentially lethal doses of UV irradiation.