Effect of non-ionic tensides on the growth of some soil bacteria

Summary The effect of some nonylphenyl-ethylene oxide polymers on the growth of Bacillus megaterium, B. cereus var. mycoides, B. polymyxa, B. subtilis, Pseudomonas fluorescence and Azotobacter chroococcum was investigated in the concentration range 20–800 ppm with the agar diffusion method. The zones of inhibition, restricted growth and eventual stimulation were determined with a Shimadzu C-930 dual wavelength TLC scanner. The data matrix was evaluated by principal component analysis. A. chroococcum was insensitive to each tenside at each concentration. The growth of the other microorganisms was inhibited by the tensides. With B. megaterium and B. cereus var. mycoides stimulation was also observed. The effect of the non-ionic tensides decreased with increasing length of the hydrophilic ethylene oxide chain. This phenomenon can be explained by the assumption that the activity of tensides depends on their membrane-damaging effect. The bulky nonylphenyl group inserts between the apolar fatty acid chains disorganizing the membrane structure. The longer hydrophilic ethylene oxide chain modifies the distribution of tenside between the apolar and polar regions of the membrane, preferring the aqueous phase. This results in the decrease or loss of biological activity. Offprint requests to: T. Cserháti     

How to assemble a beneficial microbiome in three easy steps

There is great interest in explaining how beneficial microbiomes are assembled. Antibiotic‐producing microbiomes are arguably the most abundant class of beneficial microbiome in nature, having been found on corals, arthropods, molluscs, vertebrates and plant rhizospheres. An exemplar is the attine ants, which cultivate a fungus for food and host a cuticular microbiome that releases antibiotics to defend the fungus from parasites. One explanation posits long‐term vertical transmission of Pseudonocardia bacteria, which (somehow) evolve new compounds in arms‐race fashion against parasites. Alternatively, attines (somehow) selectively recruit multiple, non‐coevolved actinobacterial genera from the soil, enabling a ‘multi‐drug’ strategy against parasites. We reconcile the models by showing that when hosts fuel interference competition by providing abundant resources, the interference competition favours the recruitment of antibiotic‐producing (and ‐resistant) bacteria. This partner‐choice mechanism is more effective when at least one actinobacterial symbiont is vertically transmitted or has a high immigration rate, as in disease‐suppressive soils.     

Proton conduction in lecithins. III. Nature of charge carriers

The nature of charge carriers was studied in hydrated lecithin using different techniques. The current-voltage characteristics confirmed the ionic nature of conduction. Attempts to determine the charge mobility were unsuccessful. From measurements of the thermovoltage at different hydration levels the charge carrier was found to be positive. The value of the thermo electromotive force (thermo e.m.f.) depends on the phase state of the lipid but is independent of its water content. The mechanism of charge generation is discussed. The activation energy of conduction does not reflect the phase change directly. Its dependence on water content is attributed to charge mobility which involves the motion of the head groups. Electrolysis experiments were carried out and the amount of hydrogen evolved was determined by gas chromatography. A proton mechanism of conduction is suggested.     

Soluble Components of Adenovirus Type 8

Soluble components of type 8 adenovirus have been studied. Four different components were isolated by anion-exchange chromatography and purified by further chromatographic procedures, by zonal centrifugation, and by erythrocyte absorption and elution. The four components exhibited the following characteristics. (i) Fiber antigen was trypsin-resistant and functioned as incomplete hemagglutinin (agglutinated rat and human erythrocytes only in the presence of certain types of adenovirus antisera). (ii) The penton was trypsin-sensitive, exerted a cytotoxic effect, and also showed incomplete hemagglutination, being active in the presence of a majority of heterotypic adenovirus antisera studied. (iii) The group-specific hexon antigen reacted in complement fixation reaction and gel precipitation with sera prepared against other types of adenoviruses, besides showing characteristics indicating the presence of a type-specific antigen component. (iv) The soluble complete hemagglutinin was trypsin-sensitive, displayed cytotoxic effect, adsorbed easily to human and rat erythrocytes, and could be eluted from them by means of receptor-destroying enzyme. The three hemagglutinins of adenovirus type 8 proved to be highly unstable, and their demonstration was only successful by using a large quantity of freshly prepared concentrated virus material. Considering these conditions, a method was developed for their concentration and purification.     

Echinocandins: production and applications

The first echinocandin-type antimycotic (echinocandin B) was discovered in the 1970s. It was followed by the isolation of more than 20 natural echinocandins. These cyclic lipo-hexapeptides are biosynthesized on non-ribosomal peptide synthase complexes by different ascomycota fungi. They have a unique mechanism of action; as non-competitive inhibitors of β-1,3-glucan synthase complex they target the fungal cell wall. Results of the structure–activity relationship experiments let us develop semisynthetic derivatives with improved properties. Three cyclic lipohiexapeptides (caspofungin, micafungin and anidulafungin) are currently approved for use in clinics. As they show good fungicidal (Candida spp.) or fungistatic (Aspergillus spp.) activity against the most important human pathogenic fungi including azole-resistant strains, they are an important addition to the antifungal armamentarium. Some evidence of acquired resistance against echinocandins has been detected among Candida glabrata strains in recent years, which enhanced the importance of data collected on the mechanism of acquired resistance developing against the echinocandins. In this review, we show the structural diversity of natural echinocandins, and we summarize the emerging data on their mode of action, biosynthesis and industrial production. Their clinical significance as well as the mechanism of natural and acquired resistance is also discussed.     

Use of desmids to assess the natural conservation value of a Hungarian oxbow (Malom-Tisza,NE-Hungary)

A method recently proposed by Coesel that uses the desmid flora to assess the conservation value of aquatic habitats was applied to an alkaline and hypertrophic oxbow of the Upper Tisza river (NE Hungary). According to the macrophyte community the oxbow contains two distinct habitats, both of which provide suitable conditions for the development of a rich desmid flora. High temporal and spatial differences in the algal flora were observed in periphyton and plankton samples taken in June and August 2004. The sample of Utricularia vulgaris periphyton collected in August was characterised by the most species-rich desmid flora. The conservation value of this sample was the maximum according to Coesel’s method. The latter also proved to be useful for the assessment of the conservation value of plankton net samples taken from among the macrophytes. The use of modified rarity value calculations as recently proposed by Fehér did not significantly affect the conservation value, but different enumeration methods to quantify the floristic diversity did result in different conservation values. We found that Coesel’s desmid based method is a useful tool for assessing the conservation value of the studied oxbow. Based our results the Coesel method’s applicability and usefulness depended on (i) the sampling location (open water or macrophytic region) samples were taken from open water or from macrophytic region; and (ii) species enumeration procedures (up to 400 specimens counted, or whole droplets counted). Presented at the International Symposium Biology and Taxonomy of Green Algae V, Smolenice, June 26–29, 2007, Slovakia.     

Phylogenetic diversity of bacterial and archaeal communities inhabiting the saline Lake Red located in Sovata, Romania

Lake Red is one of the saline lakes which were formed as a consequence of salt massif dissolution at the foot of the Gurghiu Mountains (Central Romania) at the end of the nineteenth century. The lake water had approximately 15?% w/v salt content. Phylogenetic diversity of prokaryotes inhabiting the water and sediment of the lake was studied using cultivation and cultivation-independent methods following a sampling in spring 2009. According to the results of 16S rRNA gene-based denaturing gradient gel electrophoresis (DGGE), the richness of Bacteria was higher than Archaea on the basis of the number and position of dominant bands in the gel. Sequences from DGGE bands were affiliated with Gammaproteobacteria (Halomonas and Alkalilimnicola) and Bacteroidetes (Psychroflexus) as well as Euryarchaeota. Cultivation from five different saline media resulted in 101 bacterial strains of which Gammaproteobacteria (Halomonas, Marinobacter and Salinivibrio) were the most abundant. Firmicutes (Bacillus) and Alphaproteobacteria (Aurantimonas and Roseovarius) were also identified among the isolated strains. The 16S rRNA genes from 82 bacterial and 95 archaeal clones were also phylogenetically analyzed. Bacterial clones were related to various genera of Gammaproteobacteria (Alkalilimnicola, Alkalispirillum, Arhodomonas, Halomonas, Saccharospirillum), Bacteroidetes (Gracilimonas, Psychroflexus) and Alphaproteobacteria (Oceanicola, Roseinatronobacter, Roseovarius). All of the archaeal clones sequenced corresponded to a homologous cluster affiliated with Halopelagius.     

Breath-giving cooperation: critical review of origin of mitochondria hypotheses

The origin of mitochondria is a unique and hard evolutionary problem, embedded within the origin of eukaryotes. The puzzle is challenging due to the egalitarian nature of the transition where lower-level units took over energy metabolism. Contending theories widely disagree on ancestral partners, initial conditions and unfolding of events. There are many open questions but there is no comparative examination of hypotheses. We have specified twelve questions about the observable facts and hidden processes leading to the establishment of the endosymbiont that a valid hypothesis must address. We have objectively compared contending hypotheses under these questions to find the most plausible course of events and to draw insight on missing pieces of the puzzle. Since endosymbiosis borders evolution and ecology, and since a realistic theory has to comply with both domains’ constraints, the conclusion is that the most important aspect to clarify is the initial ecological relationship of partners. Metabolic benefits are largely irrelevant at this initial phase, where ecological costs could be more disruptive. There is no single theory capable of answering all questions indicating a severe lack of ecological considerations. A new theory, compliant with recent phylogenomic results, should adhere to these criteria.Reviewers: This article was reviewed by Michael W. Gray, William F. Martin and Purificación López-García.     

Tamoxifen dosing for Cre-mediated recombination in experimental bronchopulmonary dysplasia

Bronchopulmonary dysplasia (BPD) is the most common complication of preterm birth characterized by blunted post-natal lung development. BPD can be modelled in mice by exposure of newborn mouse pups to elevated oxygen levels. Little is known about the mechanisms of perturbed lung development associated with BPD. The advent of transgenic mice, where genetic rearrangements can be induced in particular cell-types at particular time–points during organogenesis, have great potential to explore the pathogenic mechanisms at play during arrested lung development. Many inducible, conditional transgenic technologies available rely on the application of the estrogen-receptor modulator, tamoxifen. While tamoxifen is well-tolerated and has been widely employed in adult mice, or in healthy developing mice; tamoxifen is not well-tolerated in combination with hyperoxia, in the most widely-used mouse model of BPD. To address this, we set out to establish a safe and effective tamoxifen dosing regimen that can be used in newborn mouse pups subjected to injurious stimuli, such as exposure to elevated levels of environmental oxygen. Our data reveal that a single intraperitoneal dose of tamoxifen of 0.2 mg applied to newborn mouse pups in 10 μl Miglyol vehicle was adequate to successfully drive Cre recombinase-mediated genome rearrangements by the fifth day of life, in a murine model of BPD. The number of recombined cells was comparable to that observed in regular tamoxifen administration protocols. These findings will be useful to investigators where tamoxifen dosing is problematic in the background of injurious stimuli and mouse models of human and veterinary disease.     

Corticotropin-releasing factor (CRF)-immunoreactive neurons in the mammillary body of the rat

Summary The presence and distribution of CRF-immunoreactive cells and nerve fibers were studied in the mammillary body of the rat, 12 days after placing various types of lesions within the hypothalamus. Anterior and anteriolateral cuts, placed in the midhypothalamus immediately behind the paraventricular nuclei resulted in an almost complete disappearance of CRF-immunoreactive fibers from the median eminence and simultaneous appearance of CRF-containing neurons in the mammillary body. Posterior or postero-lateral hypothalamic cuts carried out in front of the mammillary body caused the accumulation of CRF-immunoreactive material in neurons and neural processes located behind the cut-line. This type of intervention had no effect on the quantity of CRF fibers in the median eminence. A cut running through the central part of the mammillary body in the frontal plane resulted in appearance of CRF neurons only in the posterior half of the mammillary region. Placing a cut behind and over the mammillary body, CRF-immunoreactive neurons became detectable below the superior cut-line. No immunoreactive neurons were observed in the mammillary body when the frontal cut reached the base of the brain at the posterior border of the nucleus, leaving intact its anterior and superior connections. In all these cases when the mammillo-thalamic tract was transected, CRF neurons became detectable in the mammillary body.