Effect of Feed Restriction on Performance and Postprandial Nutrient Metabolism in Pigs Co-Infected with Mycoplasma hyopneumoniae and Swine Influenza Virus

As nutritional status and inflammation are strongly connected, feeding and nutritional strategies could be effective to improve the ability of pigs to cope with disease. The aims of this study were to investigate the impact of a feed restriction on the ability of pigs to resist and be tolerant to a coinfection with Mycoplasma hyopneumoniae (Mhp) and the European H1N1 swine influenza virus, and the consequences for nutrient metabolism, with a focus on amino acids. Two groups of specific pathogen-free pigs were inoculated with Mhp and H1N1 21 days apart. One group was fed ad libitum, the other group was subjected to a two-week 40% feed restriction starting one week before H1N1 infection. The two respective mock control groups were included. Three days post-H1N1 infection, 200 g of feed was given to pigs previously fasted overnight and serial blood samples were taken over 4 hours to measure plasma nutrient concentrations. Throughout the study, clinical signs were observed and pathogens were detected in nasal swabs and lung tissues. Feed-restricted pigs presented shorter hyperthermia and a positive mean weight gain over the 3 days post-H1N1 infection whereas animals fed ad libitum lost weight. Both infection and feed restriction reduced postprandial glucose concentrations, indicating changes in glucose metabolism. Post-prandial plasma concentrations of the essential amino acids histidine, arginine and threonine were lower in co-infected pigs suggesting a greater use of those amino acids for metabolic purposes associated with the immune response. Altogether, these results indicate that modifying feeding practices could help to prepare animals to overcome an influenza infection. Connections with metabolism changes are discussed.     

Tn1545: a conjugative shuttle transposon

Summary Tn1545, from Streptococcus pneumoniae BM4200, confers resistance to kanamycin (aphA-3), erythromycin (ermAM) and tetracycline (tetM). The 25.3 kb element is self-transferable to various Gram-positive bacterial genera where it transposes. Tn1545 was cloned in its entirety in the recombination deficient Escherichia coli HB101 where it was unstable. The three resistance genes aphA-3, ermAM and tetM were expressed but were not transferable to other E. coli cells. Tn1545 transposed from the hybrid plasmid to multiple sites of the chromosome of its new host. The element re-transposed, at a frequency of 5×10^-9, from the chromosome to various sites of a conjugative plasmid where it could be lost by apparently clean excision. The element transformed and transposed to the chromosome of Bacillus subtilis. The properties of the conjugative shuttle transposon Tn1545 may account for the recent emergence of genes from Gram-positive bacteria in Gramnegative organisms.     

Conjugative plasmid transfer from Enterococcus faecalis to Escherichia coli.

The possibility of transfer of genetic information by conjugation from gram-positive to gram-negative bacteria was investigated with a pBR322-pAM beta 1 chimeric plasmid, designated pAT191. This shuttle vector, which possesses the tra functions of the streptococcal plasmid pAM beta 1, was conjugatively transferred from Enterococcus faecalis to Escherichia coli with an average frequency of 5 x 10(-9) per donor colony formed after mating.     

Polymerization of ADP-actin and ATP-actin under sonication and characteristics of the ATP-actin equilibrium polymer

Polymerization under sonication has been developed as a new method to study the rapid polymerization of actin with a large number of elongating sites. The theory proposed assumes that filaments under sonication are maintained at a constant length by the constant input of energy. The data obtained for the reversible polymerization of ADP-actin under sonication have been successfully analyzed according to the proposed model and, therefore, validate the model. The results obtained for the polymerization of ATP-actin under sonication demonstrate the involvement of ATP hydrolysis in the polymerization process. At high actin concentration, polymerization was fast enough, as compared to ATP hydrolysis on the F-actin, to obtain completion of the reversible polymerization of ATP-actin before significant hydrolysis of ATP occurred. A critical concentration of 3 microM was determined as the ratio of the dissociation and association rate constants for the interaction of ATP-actin with the ATP filament ends in 1 mM MgCl2, 0.2 mM ATP. The plot of the rate of elongation of filaments versus actin monomer concentration exhibited an upward deviation at high actin concentration that is consistent with this result. The fact that F-actin at steady state is more stable than the ATP-F-actin polymer at equilibrium suggests that the interaction between ADP-actin and ATP-actin subunits at the end of the ATP-capped filament is much stronger than the interaction between two ATP-actin subunits.     

Stereospecific formation of 1,2-epoxypropane, 1,2-epoxybutane and 1-chloro-2,3-epoxypropane by alkene-utilizing bacteria

Resting cells of ethene grown Mycobacterium 2W produced 1,2-epoxypropane stereospecifically from propene as revealed by optical rotation, ¹H n.m.r. using a chiral shift reagent, and also by complexation gas chromatography involving a glass capillary column coated with an optically active metal chelate. The gas-liquid chromatography method allowed the rapid screening of 11 strains with regard to stereospecific formation of 1,2-epoxypropane, 1,2-epoxybutane and 1-chloro-2,3-epoxypropane. Bacteria grown on either ethene, propene or butadiene all predominantly produced the R form of 1,2-epoxypropane from propene and 1,2-epoxybutane from 1-butene while the strains tested for 1-chloro-2,3-epoxypropane production from 3-chloro-1-propene predominantly accumulated the S enantiomer.     

Evidence for the direct interaction between tightly bound divalent metal ion and ATP on actin. Binding of the lambda isomers of beta gamma-bidentate CrATP to actin

Competition between Ca2+ and Mg2+ for binding to a single high affinity site on actin has been confirmed. Occupancy of this site only by either Ca2+ or Mg2+ affects the conformation of actin and its ability to form nuclei and hydrolyze ATP. G-actin binds the beta gamma-bidentate CrATP, a substitution inert analog of metal-ATP complexes, and shows a high specificity for the lambda isomers. Binding of CrATP to ADP-actin is accompanied by the dissociation of tightly bound ADP and Ca2+. CrATP-actin shows a high tendency to form nuclei, like MgATP-actin. Polymerization of CrATP-actin is accompanied by cleavage of the gamma-phosphate, but subsequent Pi release cannot occur because the product of the reaction is the stable CrADP-Pi complex. All these results support the view that the divalent metal ion tightly bound to actin interacts with the beta- and gamma-phosphates of ATP in the nucleotide site.     

The actin binding site of thymosin beta 4 mapped by mutational analysis.

We characterized in detail the actin binding site of the small actin-sequestering protein thymosin beta 4 (T beta 4) using chemically synthesized full-length T beta 4 variants. The N-terminal part (residues 1-16) and a hexapeptide motif (residues 17-22) form separate structural entities. In both, we identified charged and hydrophobic residues that participate in the actin interaction using chemical cross-linking, complex formation in native gels and actin-sequestering experiments. Quantitative data on the activity of the variants and circular dichroism experiments allow to present a model in which the N-terminal part needs to adopt an alpha-helix for actin binding and interacts through a patch of hydrophobic residues (6M-I-F12) on one side of this helix. Also, electrostatic contacts between actin and lysine residues 18, in the motif, and 14, in the N-terminal alpha-helix, appear important for binding. The residues critical for contacting actin are conserved throughout the beta-thymosin family and in addition to this we identify a similar pattern in the C-terminal headpiece of villin and dematin.     

Widespread formation of intracellular calcium carbonates by the bloom-forming cyanobacterium Microcystis

The formation of intracellular amorphous calcium carbonates (iACC) has been recently observed in a few cultured strains of Microcystis, a potentially toxic bloom-forming cyanobacterium found worldwide in freshwater ecosystems. If iACC-forming Microcystis are abundant within blooms, they may represent a significant amount of particulate Ca. Here, we investigate the significance of iACC biomineralization by Microcystis. First, the presence of iACC-forming Microcystis cells has been detected in several eutrophic lakes, indicating that this phenomenon occurs under environmental conditions. Second, some genotypic (presence/absence of ccyA, a marker gene of iACC biomineralization) and phenotypic (presence/absence of iACC) diversity have been detected within a collection of strains isolated from one single lake. This illustrates that this trait is frequent but also variable within Microcystis even at a single locality. Finally, one-third of publicly available genomes of Microcystis were shown to contain the ccyA gene, revealing a wide geographic and phylogenetic distribution within the genus. Overall, the present work shows that the formation of iACC by Microcystis is common under environmental conditions. While its biological function remains undetermined, this process should be further considered regarding the biology of Microcystis and implications on the Ca geochemical cycle in freshwater environments.     

Cyclitol metabolism is a central feature of Burkholderia leaf symbionts

The symbioses between plants of the Rubiaceae and Primulaceae families with Burkholderia bacteria represent unique and intimate plant–bacterial relationships. Many of these interactions have been identified through PCR-dependent typing methods, but there is little information available about their functional and ecological roles. We assembled 17 new endophyte genomes representing endophytes from 13 plant species, including those of two previously unknown associations. Genomes of leaf endophytes belonging to Burkholderia s.l. show extensive signs of genome reduction, albeit to varying degrees. Except for one endophyte, none of the bacterial symbionts could be isolated on standard microbiological media. Despite their taxonomic diversity, all endophyte genomes contained gene clusters linked to the production of specialized metabolites, including genes linked to cyclitol sugar analog metabolism and in one instance non-ribosomal peptide synthesis. These genes and gene clusters are unique within Burkholderia s.l. and are likely horizontally acquired. We propose that the acquisition of secondary metabolite gene clusters through horizontal gene transfer is a prerequisite for the evolution of a stable association between these endophytes and their hosts.