Legume-nodulating betaproteobacteria: diversity, host range, and future prospects

Rhizobia form specialized nodules on the roots of legumes (family Fabaceae) and fix nitrogen in exchange for carbon from the host plant. Although the majority of legumes form symbioses with members of genus Rhizobium and its relatives in class Alphaproteobacteria, some legumes, such as those in the large genus Mimosa, are nodulated predominantly by betaproteobacteria in the genera Burkholderia and Cupriavidus. The principal centers of diversity of these bacteria are in central Brazil and South Africa. Molecular phylogenetic studies have shown that betaproteobacteria have existed as legume symbionts for approximately 50 million years, and that, although they have a common origin, the symbiosis genes in both subclasses have evolved separately since then. Additionally, some species of genus Burkholderia, such as B. phymatum, are highly promiscuous, effectively nodulating several important legumes, including common bean (Phaseolus vulgaris). In contrast to genus Burkholderia, only one species of genus Cupriavidus (C. taiwanensis) has so far been shown to nodulate legumes. The recent availability of the genome sequences of C. taiwanensis, B. phymatum, and B. tuberum has paved the way for a more detailed analysis of the evolutionary and mechanistic differences between nodulating strains of alpha- and betaproteobacteria. Initial analyses of genome sequences have suggested that plant-associated Burkholderia spp. have lower G+C contents than Burkholderia spp. that are opportunistic human pathogens, thus supporting previous suggestions that the plant- and human-associated groups of Burkholderia actually belong in separate genera.     

Effect of energetic constraints on distribution and winter survival of weasel males

1. The absolute energy needs of small animals are generally lower than those of larger animals. This should drive higher mortality of larger animals, when the environmental conditions deteriorate. However, demonstration of the effect of energy constraints on survivals proved difficult, because the range of body mass within species is generally too small to produce enough variation for studying such an effect. An opportunity for an intraspecific study comes from weasels inhabiting the Bia?owie?a Forest (north-eastern Poland), which are characterized by a threefold variation in body mass. 2. We assumed that in summer larger weasel males are favoured by sexual selection, because they are more successful when competing for mates. We then tested whether they suffer higher mortality in winter, because they have difficulty finding sufficient food to satisfy their energy needs and/or because the additional foraging time would result in increased exposure to predation. 3. We measured daily energy expenditures (DEE) of overwintering weasel males using the doubly labelled water (DLW) technique. We constructed an energetic model predicting how individuals of different size are able to balance their energy budgets feeding on large and small prey while minimizing time spent hunting, thereby reducing their own exposure to predation. 4. The range of body mass in overwintering weasels predicted by our model corresponded very well with the distribution of prey body mass in three different habitats within our study area. Larger individuals were able to compensate for higher food requirements by using habitats with larger prey species than those available to smaller male weasels. This effectively offset the expected negative association between body mass and winter survival predicted from considerations of energy balance. 5. Our results show how energetic constraints affect body mass and spatial segregation of a species at the intra-specific level not only across large geographical ranges, but also within a relatively small area.     

Toll-like receptor 3 (TLR3) signaling requires TLR4 Interactor with leucine-rich REPeats (TRIL)

Toll-like receptors (TLRs) are a family of proteins that act as the primary sensors of microbial products. Many TLRs require accessory molecules in order to recognize these microbial products and initiate signal transduction cascades. We have identified TRIL (TLR4 interactor with leucine-rich repeats) as a novel modulator of TLR4 signaling showing high expression in the brain. We now show that TRIL also plays a role in TLR3 signaling. TRIL is expressed intracellularly in the astrocytoma cell line U373 and in the monocytic cell line THP1. TRIL co-localizes with the endosomal compartment. These data are consistent with a role for TRIL in TLR3 signaling and endosomal TLR4 signaling. TRIL was induced by the TLR3 ligand poly(I:C). Overexpression of TRIL enhanced cytokine production and interferon-stimulated response element (ISRE) luciferase activity following poly(I:C) stimulation in U373. TRIL interacted with TLR3, and this interaction was enhanced following poly(I:C) stimulation. Transient knockdown of TRIL with siRNA or stable knockdown using shRNA in U373 cells inhibited TLR3 signaling, reducing ISRE luciferase, RANTES, and type I interferon production. Knockdown of TRIL did not affect TLR2 signaling. Most accessory molecules identified to date, such as CD14, gp96, PRAT4a, and Unc93B, all play roles in multiple TLR signaling pathways, and we now show that this is also the case for TRIL.     

Genetic differentiation in natural populations of a Keystone Bunchgrass (<Emphasis Type="Italic">Aristida stricta</Emphasis>) across its native range

Aristida stricta Michx. (Poaceae) is a perennial bunchgrass native to the Southeastern Coastal Plain of North America where it is a keystone species in the longleaf pine savannas and slash pine flatwoods from southeastern North Carolina to Florida, and westward to the coast of Mississippi. We examined genetic relationships within and among ten populations of A. stricta by using eight inter-simple sequence repeat (ISSR) markers to generate band frequency data for 32 individuals from each sampled population. An analysis of molecular variance showed that 38% of the variation resided among populations while 62% was attributable to variation within populations. Grouping the populations by habitat or by geographic location did not show significant differentiation between the groups. Overall, pair-wise geographic and genetic distances were not correlated. Data indicate that while individuals within each population are genetically diverse, there seemingly are barriers to gene flow across populations leading to their divergence. Each population contains several exclusive loci suggesting that limited gene flow and/or genetic drift are likely leading to this pattern of localization. Our results, coupled with those of the previous studies that presented evidence for local adaptation and phenotypic differences among populations, suggest that there is sufficient differentiation among populations of this species to warrant: (1) maintenance of the existing genetic diversity at individual sites, and (2) use of local seed and plant sources for conservation projects.     

ORGANIC CARBON SUPPLEMENTATION OF STERILIZED MUNICIPAL WASTEWATER IS ESSENTIAL FOR HETEROTROPHIC GROWTH AND REMOVING AMMONIUM BY THE MICROALGA CHLORELLA VULGARIS1

Heterotrophic growth of the microalga Chlorella vulgaris Beij. in synthetic as well as sterilized municipal wastewater of a nonindustrialized city was measured. The city wastewater contained high levels of ammonium and nitrate, medium levels of phosphate, and low levels of nitrite and organic molecules and could not support heterotrophic growth of C. vulgaris. Evaluation of 11 known carbon sources for this microalga that were added to standard synthetic wastewater containing the same levels of nitrogen and phosphorus as the municipal wastewater revealed that the best carbon sources for heterotrophic growth were Na‐acetate and d ‐glucose. These provided the highest growth rates and the largest removal of ammonium. Growth increased with concentration of the supplement to an optimum at 0.12 M Na‐acetate. This carbon source was consumed completely within 10 d of incubation. Higher concentrations inhibited the growth of C. vulgaris. The microalgal populations under heterotrophic growth conditions were one level of magnitude higher than that under autotrophic growth conditions that served as a comparison. No growth occurred in the dark in the absence of a carbon source. Na‐acetate was superior to d ‐glucose. In municipal wastewater, when Na‐acetate or d ‐glucose was added, C. vulgaris significantly enhanced ammonium removal under heterotrophic conditions, and its capacity was equal to ammonium removal under autotrophic growth conditions. This study showed that sterilized wastewater can be treated by C. vulgaris under heterotrophic conditions if supplemented with the appropriate organic carbon source for the microalgae.     

Endogenous cannabinoid receptor agonist anandamide induces peripheral antinociception by activation of ATP-sensitive K+ channels

AimsThe effects of several potassium (K⁺) channel blockers were studied to determine which K⁺ channels are involved in peripheral antinociception induced by the cannabinoid receptor agonist, anandamide.Main methodsHyperalgesia was induced by subcutaneous injection of 250 μg carrageenan into the plantar surface of the hind paw of rats. The extent of hyperalgesia was measured using a paw pressure test 3 h following carrageenan injection. The weight in grams (g) that elicited a nociceptive response, paw flexion, during the paw pressure test was used as the nociceptive response threshold.Key findingsDoses of 50, 75, and 100 ng of anandamide elicited a dose-dependent antinociceptive effect. Following a 100 ng dose of anandamide no antinociception was observed in the paw that was contralateral to the anandamide injection site, which shows that anandamide has a peripheral site of action. Pretreatment with 20, 40 and 80 μg AM251, a CB₁ receptor antagonist, caused a dose-dependent decrease in anandamide-induced antinociception, suggesting that the CB₁ receptor is directly involved in anandamide effect. Treatment with 40, 80 and 160 μg glibenclamide, an ATP-sensitive K⁺ channel blocker, caused a dose-dependent reversal of anandamide-induced peripheral antinociception. Treatment with other K⁺ channel antagonists, tetraethylammonium (30 μg), paxilline (10 μg) and dequalinium (50 μg), had no effect on the induction of peripheral antinociception by anandamide.SignificanceThis study provides evidence that the peripheral antinociceptive effect of the cannabinoid receptor agonist, anandamide, is primarily caused by activation of ATP-sensitive K⁺ channels and does not involve other potassium channels.     

High vancomycin resistance among biofilms produced by Staphylococcus species isolated from central venous catheters

Biofilm production is an important mechanism that allows microbes to escape host defences and antimicrobial therapy. Vancomycin has been used largely for the treatment of methicillin-resistant staphylococcal infections. Here, we determined the minimal inhibitory concentration (MIC) and minimal biofilm eradication concentration (MBEC) for 82 Staphylococcus species isolated from central venous catheters (CVC). Our results showed that the 41 strong and moderate-biofilm-producing isolates presented a higher MBEC/MIC ratio for vancomycin than the 24 weak-biofilm-producing isolates, illustrating the importance of biofilm production ability and the difficulty in treating biofilm-related infections. The MBEC was significantly higher in moderate-biofilm-producing isolates than in weak-biofilm-producing isolates (p < 0.001) and in strong-biofilm-producing isolates than in weak-biofilm-producing isolates (p = 0.001). The correlation between the MIC and the MBEC was poor. Based on our results, we recommend that bacterial biofilms be suspected in all cases of CVC infection.