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Control of Virulence by the Two-Component System CiaR/H Is Mediated via HtrA, a Major Virulence Factor of Streptococcus pneumoniae. Yasser Musa Ibrahim, 2004.The CiaR/H two-component system is involved in regulating virulence and competence in Streptococcus pneumoniae . The system is known to regulate many genes, including that for high-temperature requirement A (HtrA) . This gene has been implicated in the ability of the pneumococcus to colonize the nasopharynx of infant rats . We reported previously that deletion of the gene for HtrA made the pneumococcal strains much less virulent in mouse models, less able to grow at higher temperatures, and more sensitive to oxidative stress . In this report, we show that the growth phenotype as well as sensitivity to oxidative stress of  ciaR
mutant was very similar to that of a
htrA
mutant and that the expression of the HtrA protein was reduced in a
ciaR-null mutant . Both the in vitro phenotype and the reduced
virulence of
ciaR
mutant could be restored by increasing the expression of HtrA .
Phenotypic and Molecular Typing of Salmonella Strains Reveals Different Contamination Sources in Two Commercial Pig Slaughterhouses. Nadine Botteldoorn, 2004.This study aimed to define the origin of Salmonella contamination on swine carcasses and the distribution of Salmonella serotypes in two commercial slaughterhouses during normal activity . Salmonellae were isolated from carcasses, from colons and mesenteric lymph nodes of individual pigs, and from the slaughterhouse environment . All strains were serotyped; Salmonella enterica serotype Typhimurium and Salmonella enterica serotype Derby isolates were additionally typed beyond the serotype level by pulsed-field gel electrophoresis (PFGE) and antibiotic resistance profiling (ARP); and a subset of 31 serotype Typhimurium strains were additionally phage typed . PFGE and ARP had the same discriminative possibility . Phage typing in combination with PFGE could give extra information for some strains . In one slaughterhouse, 21% of the carcasses were contaminated, reflecting a correlation with the delivery of infected pigs . Carcass contamination did not result only from infection of the corresponding pig; only 25% of the positive carcasses were contaminated with the same serotype or genotype found in the corresponding feces or mesenteric lymph nodes . In the other slaughterhouse, 70% of the carcasses were contaminated, and only in 4% was the same genotype or serotype detected as in the feces of the corresponding pigs . The other positive carcasses in both slaughterhouses were contaminated by genotypes present in the feces or lymph nodes of pigs slaughtered earlier that day or from dispersed sources in the environment . In slaughterhouses, complex contamination cycles may be present, resulting in the isolation of many different genotypes circulating in the environment due to the supply of positive animals and in the contamination of carcasses, probably through aerosols . PduA Is a Shell Protein of Polyhedral Organelles Involved in Coenzyme B12-Dependent Degradation of 1,2-Propanediol in Salmonella enterica Serovar Typhimurium LT2. Gregory D. Havemann, 2002.Salmonella enterica forms polyhedral organelles involved in coenzyme B12-dependent 1,2-propanediol degradation . These organelles are thought to consist of a proteinaceous shell that encases coenzyme B12-dependent diol dehydratase and perhaps other enzymes involved in 1,2-propanediol degradation . The function of these organelles is unknown, and no detailed studies of their structure have been reported . Genes needed for organelle formation and for 1,2-propanediol degradation are located at the 1,2-propanediol utilization (pdu) locus, but the specific genes involved in organelle formation have not been identified . Here, we show that the pduA gene encodes a shell protein required for the formation of polyhedral organelles involved in coenzyme B12-dependent 1,2-propanediol degradation . A His6-PduA fusion protein was purified from a recombinant Escherichia coli strain and used for the preparation of polyclonal antibodies . The anti-PduA antibodies obtained were partially purified by a subtraction procedure and used to demonstrate that the PduA protein localized to the shell of the polyhedral organelles . In addition, electron microscopy studies established that strains with nonpolar pduA mutations were unable to form organelles . These results show that the pduA gene is essential for organelle formation and indicate that the PduA protein is a structural component of the shell of these organelles . Physiological studies of nonpolar pduA mutants were also conducted . Such mutants grew similarly to the wild-type strain at low concentrations of 1,2-propanediol but exhibited a period of interrupted growth in the presence of higher concentrations of this growth substrate . Growth tests also showed that a nonpolar pduA deletion mutant grew faster than the wild-type strain at low vitamin B12 concentrations . These results suggest that the polyhedral organelles formed by S . enterica during growth on 1,2-propanediol are not involved in the concentration of 1,2-propanediol or coenzyme B12, but are consistent with the hypothesis that these organelles moderate aldehyde production to minimize toxicity . The Abundance of Microcystin-Producing Genotypes Correlates Positively with Colony Size in Microcystis sp . and Determines Its Microcystin Net Production in Lake Wannsee. Rainer Kurmayer, 2003.The working hypotheses tested on a natural population of Microcystis sp . in Lake Wannsee (Berlin, Germany) were that (i) the varying abundance of microcystin-producing genotypes versus non-microcystin-producing genotypes is a key factor for microcystin net production and (ii) the occurrence of a gene for microcystin net production is related to colony morphology, particularly colony size . To test these hypotheses, samples were fractionated by colony size with a sieving procedure during the summer of 2000 . Each colony size class was analyzed for cell numbers, the proportion of microcystin-producing genotypes, and microcystin concentrations . The smallest size class of Microcystis colonies (<50 µm) showed the lowest proportion of microcystin-producing genotypes, the highest proportion of non-microcystin-producing cells, and the lowest microcystin cell quotas (sum of microcystins RR, YR, LR, and WR) . In contrast, the larger size classes of Microcystis colonies (>100 µm) showed the highest proportion of microcystin-producing genotypes, the lowest proportion of non-microcystin-producing cells, and the highest microcystin cell quotas . The microcystin net production rate was nearly one to one positively related to the population growth rate for the larger colony size classes (>100 µm); however, no relationship could be found for the smaller size classes . It was concluded that the variations found in microcystin net production between colony size classes are chiefly due to differences in genotype composition and that the microcystin net production in the lake is mainly influenced by the abundance of the larger (>100-µm) microcystin-producing colonies .
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