Regional analysis of litter quality in the central grassland region of North America

Abstract. The central grassland region of North America is characterized by large gradients of temperature and precipitation. These climatic variables are important determinants of the distribution of plant species, and strongly influence plant morphology and tissue chemistry. We analysed regional patterns of plant litter quality as they vary with climate in grassland ecosystems throughout central North America including tall‐grass prairie, mixed grass prairie, shortgrass steppe, and hot desert grasslands. An extensive database from the International Biological Program and the Long‐Term Ecological Research Program allowed us to isolate the effects of climate from those of plant functional types on litter quality. Our analysis of grass species confirms a previously recognized positive correlation between C/N ratios and precipitation. Precipitation exhibited a similar positive relationship with lignin/N and percent lignin. Although there was no significant correlation between temperature and C/N, there was a significant positive relationship between temperature and both percent lignin and lignin/N. Among functional types, C₃ grasses had a slightly lower C/N ratio than C₄ grasses. Tall grass species exhibited higher C/N, lignin/N, and percent lignin than short grass species. This understanding of the regional patterns of litter quality and the factors controlling them provides us with a greater knowledge of the effect that global change and the accompanying feedbacks may have on ecosystem processes.     

Conservation of bacterial protein synthesis machinery: initiation and elongation in Mycobacterium smegmatis

Most of our understanding of ribosome function is based on experiments utilizing translational components from Escherichia coli. It is not clear to which extent the details of translation mechanisms derived from this single organism are true for all bacteria. Here we investigate translation factor-dependent reactions of initiation and elongation in a reconstituted translation system from a Gram-positive bacterium Mycobacterium smegmatis. This organism was chosen because mutations in rRNA have very different phenotypes in E. coli and M. smegmatis, and the docking site for translational GTPases, the L12 stalk, is extended in the ribosomes from M. smegmatis compared to E. coli. M. smegmatis genes coding for IF1, IF2, IF3, EF-G, and EF-Tu were identified by sequence alignments; the respective recombinant proteins were prepared and studied in a variety of biochemical and biophysical assays with M. smegmatis ribosomes. We found that the activities of initiation and elongation factors and the rates of elemental reactions of initiation and elongation of protein synthesis are remarkably similar with M. smegmatis and E. coli components. The data suggest a very high degree of conservation of basic translation mechanisms, probably due to coevolution of the ribosome components and translation factors. This work establishes the reconstituted translation system from individual purified M. smegmatis components as an alternative to that from E. coli to study the mechanisms of translation and to test the action of antibiotics against Gram-positive bacteria.     

Metabolism of 35S-labelled Antithyroid Drugs in Man

Differences in the metabolic fate of antithyroid drugs influence the optimal frequency of administration and their therapeutic efficacy. ³⁵S propylthiouracil differed from the ³⁵S imidazoles (carbimazole and methimazole) in the more rapid absorption and excretion and the shorter biological half-life in the plasma of the former. Renal function may have a more important influence on the biological half-life of the drugs than thyroid status. Further work is required to determine the optimal frequency of administration for each compound.     

Titanium with nanotopography induces osteoblast differentiation through regulation of integrin αV

Topographical modifications of titanium (Ti) at the nanoscale level generate surfaces that regulate several signaling pathways and cellular functions, which may affect the process of osseointegration. Here, we investigated the participation of integrin αV in the osteogenic capacity of Ti with nanotopography. Machined titanium discs (untreated) were submitted to treatment with H₂SO₄/H₂O₂ to produce the nanotopography (nanostructured). First, the greater osteogenic capacity of the nanotopography that increased osteoblast differentiation of mesenchymal stem cells compared with untreated topography was shown. Also, the nanostructured surface increased (regulation ≥ 1.9-fold) the gene expression of 6 integrins from a custom array plate utilized to evaluate the gene expression of 84 genes correlated with cell adhesion signaling pathway, including integrin αV, which is involved in osteoblast differentiation. By silencing integrin αV in MC3T3-E1 cells cultured on nanotopography, the impairment of osteoblast differentiation induced by this surface was observed. In conclusion, it was shown that nanotopography regulates the expression of several components of the cell adhesion signaling pathway and its higher osteogenic potential is, at least in part, due to its ability to upregulate the expression of integrin αV. Together with previous data that showed the participation of integrins α1, β1, and β3 in the nanotopography osseoinduction activity, we have uncovered the pivotal role of this family of membrane receptors in the osteogenic potential of this surface.     

Recognition in a Social Symbiosis: Chemical Phenotypes and Nestmate Recognition Behaviors of Neotropical Parabiotic Ants

Social organisms rank among the most abundant and ecologically dominant species on Earth, in part due to exclusive recognition systems that allow cooperators to be distinguished from exploiters. Exploiters, such as social parasites, manipulate their hosts’ recognition systems, whereas cooperators are expected to minimize interference with their partner’s recognition abilities. Despite our wealth of knowledge about recognition in single-species social nests, less is known of the recognition systems in multi-species nests, particularly involving cooperators. One uncommon type of nesting symbiosis, called parabiosis, involves two species of ants sharing a nest and foraging trails in ostensible cooperation. Here, we investigated recognition cues (cuticular hydrocarbons) and recognition behaviors in the parabiotic mixed-species ant nests of Camponotus femoratus and Crematogaster levior in North-Eastern Amazonia. We found two sympatric, cryptic Cr. levior chemotypes in the population, with one type in each parabiotic colony. Although they share a nest, very few hydrocarbons were shared between Ca. femoratus and either Cr. levior chemotype. The Ca. femoratus hydrocarbons were also unusually long–chained branched alkenes and dienes, compounds not commonly found amongst ants. Despite minimal overlap in hydrocarbon profile, there was evidence of potential interspecific nestmate recognition –Cr. levior ants were more aggressive toward Ca. femoratus non-nestmates than Ca. femoratus nestmates. In contrast to the prediction that sharing a nest could weaken conspecific recognition, each parabiotic species also maintains its own aggressive recognition behaviors to exclude conspecific non-nestmates. This suggests that, despite cohabitation, parabiotic ants maintain their own species-specific colony odors and recognition mechanisms. It is possible that such social symbioses are enabled by the two species each using their own separate recognition cues, and that interspecific nestmate recognition may enable this multi-species cooperative nesting.     

Gene Content and Diversity of the Loci Encoding Biosynthesis of Capsular Polysaccharides of the 15 Serovar Reference Strains of Haemophilus parasuis

Haemophilus parasuis is the causative agent of Glässer''s disease, a systemic disease of pigs, and is also associated with pneumonia. H. parasuis can be classified into 15 different serovars. Here we report, from the 15 serotyping reference strains, the DNA sequences of the loci containing genes for the biosynthesis of the group 1 capsular polysaccharides, which are potential virulence factors of this bacterium. We contend that these loci contain genes for polysaccharide capsule structures, and not a lipopolysaccharide O antigen, supported by the fact that they contain genes such as wza, wzb, and wzc, which are associated with the export of polysaccharide capsules in the current capsule classification system. A conserved region at the 3′ end of the locus, containing the wza, ptp, wzs, and iscR genes, is consistent with the characteristic export region 1 of the model group 1 capsule locus. A potential serovar-specific region (region 2) has been found by comparing the predicted coding sequences (CDSs) in all 15 loci for synteny and homology. The region is unique to each reference strain with the exception of those in serovars 5 and 12, which are identical in terms of gene content. The identification and characterization of this locus among the 15 serovars is the first step in understanding the genetic, molecular, and structural bases of serovar specificity in this poorly studied but important pathogen and opens up the possibility of developing an improved molecular serotyping system, which would greatly assist diagnosis and control of Glässer''s disease.