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Detection of Enterotoxigenic Clostridium perfringens Type A Isolates in American Retail Foods. Qiyi Wen, 2004.Currently there is only limited understanding of the reservoirs for Clostridium perfringens type A food poisoning . A recent survey (Y.-T . Lin and R . Labbe, Appl . Environ . Microbiol . 69:1642-1646, 2003) of non-outbreak American retail foods did not identify the presence of a single C . perfringens isolate carrying the enterotoxin gene (cpe) necessary for causing food poisoning . The present study revisited this issue, using revised methodology and food sampling strategies . In our survey, cpe-positive C . perfringens isolates were detected in  1.4% of
900 surveyed non-outbreak American retail foods . Interestingly, those enterotoxigenic isolates in non-outbreak foods appear indistinguishable from C . perfringens isolates known to cause food poisoning outbreaks: i.e., the enterotoxigenic retail food isolates all carry a chromosomal cpe gene, are classified as type A, and exhibit exceptional heat resistance . Collectively, these findings indicate that some American foods are contaminated, at the time of retail purchase, with C . perfringens isolates having full potential to cause food poisoning . Furthermore, demonstrating that type A isolates carrying a chromosomal cpe gene are the enterotoxigenic isolates most commonly present in foods helps to explain why these isolates (rather than type A isolates carrying a plasmid cpe gene or cpe-positive type C or D isolates) are strongly associated with food poisoning outbreaks . Finally, since type A chromosomal cpe isolates present in the surveyed raw foods exhibited strong heat resistance, it appears that exceptional heat resistance is not a survivor trait selected for by cooking but is instead an intrinsic trait possessed by many type A chromosomal cpe isolates .
Alkaline Anaerobic Respiration: Isolation and Characterization of a Novel Alkaliphilic and Metal-Reducing Bacterium. Qi Ye, 2004.Iron-reducing enrichments were obtained from leachate ponds at the U.S . Borax Company in Boron, Calif . Based on partial small-subunit (SSU) rRNA gene sequences (approximately 500 nucleotides), six isolates shared 98.9% nucleotide identity . As a representative, the isolate QYMF was selected for further analysis . QYMF could be grown with Fe(III)-citrate, Fe(III)-EDTA, Co(III)-EDTA, or Cr(VI) as electron acceptors, and yeast extract and lactate could serve as electron donors . Growth during iron reduction occurred over the pH range of 7.5 to 11.0 (optimum, pH 9.5), a sodium chloride range of 0 to 80 g/liter (optimum, 20 g/liter), and a temperature range of 4 to 45°C (optimum, approximately 35°C), and iron precipitates were formed . QYMF was a strict anaerobe that could be grown in the presence of borax, and the cells were straight rods that produced endospores . Sodium chloride and yeast extract stimulated growth . Phylogenetic analysis of the SSU rRNA gene indicated that the bacterium was a low-G+C gram-positive microorganism and had 96 and 92% nucleotide identity with Alkaliphilus transvaalensis and Alkaliphilus crotonatoxidans, respectively . The major phospholipid fatty acids were 14:1, 16:1  7c, and 16:0, which were different from those of other alkaliphiles but similar to those of reported iron-reducing bacteria . The results demonstrated that the isolate might represent a novel metal-reducing alkaliphilic species . The name Alkaliphilus metalliredigens sp . nov . is proposed . The isolation and activity of metal-reducing bacteria from borax-contaminated leachate ponds suggest that bioremediation of metal-contaminated alkaline environments may be feasible and have implications for alkaline anaerobic respiration .
Mutations in rpoBC Suppress the Defects of a Sinorhizobium meliloti relA Mutant. Derek H. Wells, 2003.The nitrogen-fixing symbiosis between Sinorhizobium meliloti and Medicago sativa requires complex physiological adaptation by both partners . One method by which bacteria coordinately control physiological adaptation is the stringent response, which is triggered by the presence of the nucleotide guanosine tetraphosphate (ppGpp) . ppGpp, produced by the RelA enzyme, is thought to bind to and alter the ability of RNA polymerase (RNAP) to initiate and elongate transcription and affect the affinity of the core enzyme for various sigma factors . An S . meliloti relA mutant which cannot produce ppGpp was previously shown to be defective in the ability to form nodules . This mutant also overproduces a symbiotically necessary exopolysaccharide called succinoglycan () . The work presented here encompasses the analysis of suppressor mutants, isolated from host plants, that suppress the symbiotic defects of the relA mutant . All suppressor mutations are extragenic and map to either rpoB or rpoC, which encode the ß and ß' subunits of RNAP . Phenotypic, structural, and gene expression analyses reveal that suppressor mutants can be divided into two classes; one is specific in its effect on stringent response-regulated genes and shares striking similarity with suppressor mutants of Escherichia coli strains that lack ppGpp, and another reduces transcription of all genes tested in comparison to that in the relA parent strain . Our findings indicate that the ability to successfully establish symbiosis is tightly coupled with the bacteria's ability to undergo global physiological adjustment via the stringent response .
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