Dimorphism in methane seep-dwelling ecotypes of the largest known bacteria

We present evidence for a dimorphic life cycle in the vacuolate sulfide-oxidizing bacteria that appears to involve the attachment of a spherical Thiomargarita-like cell to the exteriors of invertebrate integuments and other benthic substrates at methane seeps. The attached cell elongates to produce a stalk-like form before budding off spherical daughter cells resembling free-living Thiomargarita that are abundant in surrounding sulfidic seep sediments. The relationship between the attached parent cell and free-living daughter cell is reminiscent of the dimorphic life modes of the prosthecate Alphaproteobacteria, but on a grand scale, with individual elongate cells reaching nearly a millimeter in length. Abundant growth of attached Thiomargarita-like bacteria on the integuments of gastropods and other seep fauna provides not only a novel ecological niche for these giant bacteria, but also for animals that may benefit from epibiont colonization.     

Village trial of bednets impregnated with wash-resistant permethrin compared with other pyrethroid formulations

Abstract. A village-scale field trial of pyrethroid-impregnated mosquito nets was undertaken in The Gambia, West Africa, in the Mandinka village of Saruja (13^o13'N, 14^o55'W) during July-November 1989. Nearly all the villagers possessed and used their own bednets. Anopheles gambiae is the main vector of human malaria in the area.
An experimental wash-resistant formulation of permethrin was compared with standard emulsifiable concentrate (EC) formulations of permethrin and lambda-cyhalothrin, versus placebo-treated bednets. Target concentrations of pyrethroids on bednets were permethrin 500mg/m² and lambda-cyhalothrin 25 mg/m². The experimental design involved random allocation of a treatment to one net per family. Whereas 68% of people questioned said they washed their nets fortnightly, observations during the 16-week trial period showed that only 4/130 (3%) of nets involved in the trial had been washed as frequently as once per month.
Early morning searches for mosquitoes under bednets (1 day/week for 16 weeks) found significantly more mosquitoes (60% An. gambiae ) in placebo-treated nets than in pyrethroid-treated nets. The numbers found with each of the three pyrethroid treatments did not differ significantly from each other. Insecticidal efficacy of the treatments was tested by bioassays using wild-caught unfed mosquitoes exposed to netting for 3min. Linear regression analysis of bioassay mortality against number of times that a net had been washed by villagers showed that nets impregnated with the wash-resistant permethrin retained their insecticidal properties better than nets impregnated with lambda-cyhalothrin or with the standard permethrin formulation.     

The Lys 280 → Gln mutation mimicking disease‐linked acetylation of Lys 280 in tau extends the structural core of fibrils and modulates their catalytic properties

Amyloid fibrillar aggregates isolated from the brains of patients with neurodegenerative diseases invariably have post‐translational modifications (PTMs). The roles that PTMs play in modulating the structures and polymorphism of amyloid aggregates, and hence their ability to catalyze the conversion of monomeric protein to their fibrillar structure is, however, poorly understood. This is particularly true in the case of tau aggregates, where specific folds of fibrillar tau have been implicated in specific tauopathies. Several PTMs, including acetylation at Lys 280, increase aggregation of tau in the brain, and increase neurodegeneration. In this study, tau‐K18 K280Q, in which the Lys 280 → Gln mutation is used to mimic acetylation at Lys 280, is shown, using HX‐MS measurements, to form fibrils with a structural core that is longer than that of tau‐K18 fibrils. Measurements of critical concentrations show that the binding affinity of monomeric tau‐K18 for its fibrillar counterpart is only marginally more than that of monomeric tau‐K18 K280Q for its fibrillar counterpart. Quantitative analysis of the kinetics of seeded aggregation, using a simple Michaelis–Menten‐like model, in which the monomer first binds and then undergoes conformational conversion to β‐strand, shows that the fibrils of tau‐K18 K280Q convert monomeric protein more slowly than do fibrils of tau‐K18. In contrast, monomeric tau‐K18 K280Q is converted faster to fibrils than is monomeric tau‐K18. Thus, the effect of Lys 280 acetylation on tau aggregate propagation in brain cells is expected to depend on the amount of acetylated tau present, and on whether the propagating seed is acetylated at Lys 280 or not.     

Insulin-releasing and cytotoxic properties of the frog skin peptide,tigerinin-1R: a structure–activity study

The frog skin host-defense peptide tigerinin-1R (RVCSAIPLPICH.NH₂) is insulinotropic both in vitro and in vivo. This study investigates the effects on insulin release and cytotoxicity of changes in cationicity and hydrophobicity produced by selected substitutions of amino acids by l-arginine, l-lysine and l-tryptophan. The [A5W], [L8W] and [I10W] analogs produced a significant (P < 0.01) increase in the rate of insulin release from BRIN-BD11 rat clonal β cells at concentration of 0.01 nM compared with 0.1 nM for tigerinin-1R. The increase in the rate of insulin release produced by a 3 μM concentration of the [S4R], [H12K], and [I10W] analogs from both BRIN-BD11 cells and mouse islets was significantly greater (P < 0.05) than that produced by tigerinin-1R. No peptide stimulated the release of lactate dehydrogenase at concentrations up to 3 μM indicating that plasma membrane integrity had been preserved. [A5W] tigerinin-1R was the only analog tested that showed cytotoxic activity against human erythrocytes (LC₅₀ = 265 ± 16 μM) and inhibited growth of Escherichia coli (MIC = 500 μM) and Staphylococcus aureus (MIC = 250 μM). The circular dichroism spectra of tigerinin-1R and [A5W] tigerinin-1R indicate that the peptides adopt a mixture of β-sheet, random coil and reverse β-turn conformations in 50% trifluoroethanol/water and methanol/water. Administration of [S4R] tigerinin-1R (75 nmol/kg body weight) to high-fat fed mice with insulin resistance significantly (P < 0.05) enhanced insulin release and improved glucose tolerance over a 60 min period following an intraperitoneal glucose load. The study supports the claim that tigerinin-1R shows potential for development into novel therapeutic agents for treatment of type 2 diabetes mellitus.     

Suppression of pecan and peach pathogens on different substrates using Xenorhabdus bovienii and Photorhabdus luminescens

Prior research indicated the ability of concentrated metabolites from Xenorhabdus spp. and Photorhabdus spp. to suppress a variety of peach and pecan diseases in vitro, and on detached pecan leaves or terminals. In the current study, our objectives were to (1) determine if bacterial broths (in addition to concentrated metabolites tested previously) have suppressive ability and (2) determine if metabolites or bacterial broths are active in a soil medium. In laboratory studies, two pathogens of pecan (Fusicladium effusum and Phytophthora cactorum) and one peach pathogen (Armillaria tabescens) were tested for susceptibility to Xenorhabdus bovienii (SN) and Photorhabdus luminescens (VS) bacterial broths or concentrated metabolites on three different substrates. Treatments were applied to lesions of F. effusum on terminals to ascertain any suppressive effect on sporulation, to A. tabescens in soil to determine effect on survival of mycelia, and to lesions caused by P. cactorum on pecan leaf surfaces to assess any reduction in lesion development. Acetone (the metabolite solvent), un-inoculated media (tryptic soy broth) and water were included as controls. The X. bovienii metabolite treatment was as efficacious as a commercial fungicide (fenbuconazole) in reducing sporulation of F. effusum on pecan terminals. The P. luminescens metabolite treatment also caused reduced sporulation relative to water and acetone controls but bacterial broths had no effect. In contrast, all bacterial broth and metabolite treatments suppressed lesion growth caused by P. cactorum (measured on detached leaves maintained on agar). However, in soil, only the P. luminescens metabolite treatment was suppressive to A. tabescens (this is the first report of Photorhabdus or Xenorhabdus toxicity to Armillaria spp.). This study provides a basis for further research on the use of Xenorhabdus and Photorhabdus metabolites or bacterial broth for suppression of pecan and peach diseases.     

Malaria-induced reduction of fecundity during the first gonotrophic cycle of Anopheles Stephensi mosquitoes

Abstract. Anopheles stephensi mosquitoes which had fed upon mice infected with Plasmodium yoelii nigeriensis malaria parasites produced significantly fewer eggs than mosquitoes fed on an uninfected mouse. Fecundity reduction was more pronounced when the bloodmeal contained malaria gametocytes and the mosquitoes developed oocysts. Egg production and haematin excretion were correlated for uninfected bloodfed mosquitoes; the presence of P.y. nigeriensis in the blood affected this relationship. Reduced fecundity was associated with a significant reduction of bloodmeal size (measured by haematin excretion) in mosquitoes which ingested gametocytaemic blood. The bloodmeal size in mosquitoes fed on parasitaemic blood without gametocytes was not significantly reduced. The use of haematin assays for determination of bloodmeal size in mosquitoes is discussed.     

B‐cell capacity for differentiation changes with age

BackgroundAge‐related immune deficiencies are thought to be responsible for increased susceptibility to infection in older adults, with alterations in lymphocyte populations becoming more prevalent over time. The loss of humoral immunity in ageing was attributed to the diminished numbers of B cells and the reduced ability to generate immunoglobulin.AimsTo compare the intrinsic B‐cell capacity for differentiation into mature plasma cells (PCs), between young and old donors, using in vitro assays, providing either effective T‐cell help or activation via TLR engagement.MethodsB cells were isolated from healthy individuals, in younger (30–38 years) and older (60–64 years) donors. An in vitro model system of B‐cell differentiation was used, analysing 5 differentiation markers by flow cytometry, under T‐dependent (TD: CD40/BCR stimulation) or T‐independent (TI: TLR7/BCR activation) conditions. Antibody secretion was measured by ELISA and gene expression using qPCR.ResultsTI and TD differentiation resulted in effective proliferation of B cells followed by their differentiation into PC. B‐cell‐executed TI differentiation was faster, all differentiation marker and genes being expressed earlier than under TD differentiation (day 6), although generating less viable cells and lower antibody levels (day 13). Age‐related differences in B‐cell capacity for differentiation were minimal in TD differentiation. In contrast, in TI differentiation age significantly affected proliferation, viability, differentiation, antibody secretion and gene expression, older donors being more efficient.ConclusionAltogether, B‐cell differentiation into PC appeared similar between age groups when provided with T‐cell help, in contrast to TI differentiation, where multiple age‐related changes suggest better capacities in older donors. These new findings may help explain the emergence of autoantibodies in ageing.     

Suppression of PPARγ through MKRN1-mediated ubiquitination and degradation prevents adipocyte differentiation

The central regulator of adipogenesis, PPARγ, is a nuclear receptor that is linked to obesity and metabolic diseases. Here we report that MKRN1 is an E3 ligase of PPARγ that induces its ubiquitination, followed by proteasome-dependent degradation. Furthermore, we identified two lysine sites at 184 and 185 that appear to be targeted for ubiquitination by MKRN1. Stable overexpression of MKRN1 reduced PPARγ protein levels and suppressed adipocyte differentiation in 3T3-L1 and C3H10T1/2 cells. In contrast, MKRN1 depletion stimulated adipocyte differentiation in these cells. Finally, MKRN1 knockout MEFs showed an increased capacity for adipocyte differentiation compared with wild-type MEFs, with a concomitant increase of PPARγ and adipogenic markers. Together, these data indicate that MKRN1 is an elusive PPARγ E3 ligase that targets PPARγ for proteasomal degradation by ubiquitin-dependent pathways, and further depict MKRN1 as a novel target for diseases involving PPARγ.