Internalin profiling and multilocus sequence typing suggest four Listeria innocua subgroups with different evolutionary distances from Listeria monocytogenes

<p>Abstract</p> <p>Background</p> <p>Ecological, biochemical and genetic resemblance as well as clear differences of virulence between <it>L. monocytogenes </it>and <it>L. innocua </it>make this bacterial clade attractive as a model to examine evolution of pathogenicity. This study was attempted to examine the population structure of <it>L. innocua </it>and the microevolution in the <it>L. innocua</it>-<it>L. monocytogenes </it>clade via profiling of 37 internalin genes and multilocus sequence typing based on the sequences of 9 unlinked genes <it>gyrB</it>, <it>sigB</it>, <it>dapE</it>, <it>hisJ</it>, <it>ribC</it>, <it>purM</it>, <it>gap</it>, <it>tuf </it>and <it>betL</it>.</p> <p>Results</p> <p><it>L. innocua </it>was genetically monophyletic compared to <it>L. monocytogenes</it>, and comprised four subgroups. Subgroups A and B correlated with internalin types 1 and 3 (except the strain 0063 belonging to subgroup C) and internalin types 2 and 4 respectively. The majority of <it>L. innocua </it>strains belonged to these two subgroups. Subgroup A harbored a whole set of <it>L. monocytogenes</it>-<it>L. innocua </it>common and <it>L. innocua</it>-specific internalin genes, and displayed higher recombination rates than those of subgroup B, including the relative frequency of occurrence of recombination versus mutation (ρ/θ) and the relative effect of recombination versus point mutation (r/m). Subgroup A also exhibited a significantly smaller exterior/interior branch length ratio than expected under the coalescent model, suggesting a recent expansion of its population size. The phylogram based on the analysis with correction for recombination revealed that the time to the most recent common ancestor (TMRCA) of <it>L. innocua </it>subgroups A and B were similar. Additionally, subgroup D, which correlated with internalin type 5, branched off from the other three subgroups. All <it>L. innocua </it>strains lacked seventeen virulence genes found in <it>L. monocytogenes </it>(except for the subgroup D strain L43 harboring <it>inlJ </it>and two subgroup B strains bearing <it>bsh</it>) and were nonpathogenic to mice.</p> <p>Conclusions</p> <p><it>L. innocua </it>represents a young species descending from <it>L. monocytogenes </it>and comprises four subgroups: two major subgroups A and B, and one atypical subgroup D serving as a link between <it>L. monocytogenes </it>and <it>L. innocua </it>in the evolutionary chain. Although subgroups A and B appeared at approximately the same time, subgroup A seems to have experienced a recent expansion of the population size with higher recombination frequency and effect than those of subgroup B, and might represent the possible evolutionary direction towards adaptation to enviroments. The evolutionary history in the <it>L. monocytogenes</it>-<it>L. innocua </it>clade represents a rare example of evolution towards reduced virulence of pathogens.</p

Homotopy Iteration Algorithm for Crack Parameters Identification with Composite Element Method

An approach based on homotopy iteration algorithm is proposed to identify the crack parameters in beam structures. In the forward problem, a fully open crack model with the composite element method is employed for the vibration analysis. The dynamic responses of the cracked beam in time domain are obtained from the Newmark direct integration method. In the inverse analysis, an identification approach based on homotopy iteration algorithm is studied to identify the location and the depth of a cracked beam. The identification equation is derived by minimizing the error between the calculated acceleration response and the simulated measured one. Newton iterative method with the homotopy equation is employed to track the correct path and improve the convergence of the crack parameters. Two numerical examples are conducted to illustrate the correctness and efficiency of the proposed method. And the effects of the influencing parameters, such as measurement time duration, measurement points, division of the homotopy parameter and measurement noise, are studied

Antigenic analysis of classical swine fever virus E2 glycoprotein using pig antibodies identifies residues contributing to antigenic variation of the vaccine C-strain and group 2 strains circulating in China

BACKGROUND: Glycoprotein E2, the immunodominant protein of classical swine fever virus (CSFV), can induce neutralizing antibodies and confer protective immunity in pigs. Our previous phylogenetic analysis showed that subgroup 2.1 viruses branched away from subgroup 1.1, the vaccine C-strain lineage, and became dominant in China. The E2 glycoproteins of CSFV C-strain and recent subgroup 2.1 field isolates are genetically different. However, it has not been clearly demonstrated how this diversity affects antigenicity of the protein. RESULTS: Antigenic variation of glycoprotein E2 was observed not only between CSFV vaccine C-strain and subgroup 2.1 strains, but also among strains of the same subgroup 2.1 as determined by ELISA-based binding assay using pig antisera to the C-strain and a representative subgroup 2.1 strain QZ-07 currently circulating in China. Antigenic incompatibility of E2 proteins markedly reduced neutralization efficiency against heterologous strains. Single amino acid substitutions of D705N, L709P, G713E, N723S, and S779A on C-strain recombinant E2 (rE2) proteins significantly increased heterologous binding to anti-QZ-07 serum, suggesting that these residues may be responsible for the antigenic variation between the C-strain and subgroup 2.1 strains. Notably, a G713E substitution caused the most dramatic enhancement of binding of the variant C-strain rE2 protein to anti-QZ-07 serum. Multiple sequence alignment revealed that the glutamic acid residue at this position is conserved within group 2 strains, while the glycine residue is invariant among the vaccine strains, highlighting the role of the residue at this position as a major determinant of antigenic variation of E2. A variant Simpson's index analysis showed that both codons and amino acids of the residues contributing to antigenic variation have undergone similar diversification. CONCLUSIONS: These results demonstrate that CSFV vaccine C-strain and group 2 strains circulating in China differ in the antigenicity of their E2 glycoproteins. Systematic site-directed mutagenesis of the antigenic units has revealed residues that limit cross-reactivity. Our findings may be useful for the development of serological differential assays and improvement of immunogenicity of novel classical swine fever vaccines

CHEN AND LI

In this paper we will establish a relation between spacelike Weingarten surfaces with condition K � 2mH � m2 � l 2 in R3 1 and solutions of the sine-Gordon equation. Moreover, we will give a method to construct new spacelike Weingarten surfaces from a given spacelike Weingarten surface in R3 1 by Backlund ¨ transforma-tion. � 1997 Academic Pres

Spacelike Weingarten Surfaces inR13and the Sine-Gordon Equation

AbstractIn this paper we will establish a relation between spacelike Weingarten surfaces with conditionK+2mH=m2+l2inR13and solutions of the sine-Gordon equation. Moreover, we will give a method to construct new spacelike Weingarten surfaces from a given spacelike Weingarten surface inR13by Bäcklund transformation

Characterization of self-conjugate minimal surfaces in R&quot;3

Consiglio Nazionale delle Ricerche (CNR). Biblioteca Centrale / CNR - Consiglio Nazionale delle RichercheSIGLEITItal

Some theorems on a class of harmonic manifolds

Consiglio Nazionale delle Ricerche (CNR). Biblioteca Centrale / CNR - Consiglio Nazionale delle RichercheSIGLEITItal