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Analysis of cis- and trans-Acting Factors Involved in Regulation of the Streptococcus mutans Fructanase Gene (fruA). Zezhang T. Wen, 2002.There are two primary levels of control of the expression of the fructanase gene (fruA) of Streptococcus mutans: induction by levan, inulin, or sucrose and repression in the presence of glucose and other readily metabolized sugars . The goals of this study were to assess the functionality of putative cis-acting regulatory elements and to begin to identify the trans-acting factors involved in induction and catabolite repression of fruA. The fruA promoter and its derivatives generated by deletions and/or site-directed mutagenesis were fused to a promoterless chloramphenicol acetyltransferase (CAT) gene as a reporter, and strains carrying the transcriptional fusions were then analyzed for CAT activities in response to growth on various carbon sources . A dyadic sequence, ATGACA(TC)TGTCAT, located at -72 to -59 relative to the transcription initiation site was shown to be essential for expression of fruA . Inactivation of the genes that encode fructose-specific enzymes II resulted in elevated expression from the fruA promoter, suggesting negative regulation of fruA expression by the fructose phosphotransferase system . Mutagenesis of a terminator-like structure located in the 165-base 5' untranslated region of the fruA mRNA or insertional inactivation of antiterminator genes revealed that antitermination was not a mechanism controlling induction or repression of fruA, although the untranslated leader mRNA may play a role in optimal expression of fructanase . Deletion or mutation of a consensus catabolite response element alleviated glucose repression of fruA, but interestingly, inactivation of the ccpA gene had no discernible effect on catabolite repression of fruA . Accumulating data suggest that expression of fruA is regulated by a mechanism that has several unique features that distinguish it from archetypical polysaccharide catabolic operons of other gram-positive bacteria . The Geobacillus stearothermophilus V iscS Gene, Encoding Cysteine Desulfurase, Confers Resistance to Potassium Tellurite in Escherichia coli K-12. Juan C. Tantaleán, 2003.Many eubacteria are resistant to the toxic oxidizing agent potassium tellurite, and tellurite resistance involves diverse biochemical mechanisms . Expression of the iscS gene from Geobacillus stearothermophilus V, which is naturally resistant to tellurite, confers tellurite resistance in Escherichia coli K-12, which is naturally sensitive to tellurite . The G . stearothermophilus iscS gene encodes a cysteine desulfurase . A site-directed mutation in iscS that prevents binding of its pyridoxal phosphate cofactor abolishes both enzyme activity and its ability to confer tellurite resistance in E . coli . Expression of the G . stearothermophilus iscS gene confers tellurite resistance in tellurite-hypersensitive E . coli iscS and sodA sodB mutants (deficient in superoxide dismutase) and complements the auxotrophic requirement of an E . coli iscS mutant for thiamine but not for nicotinic acid . These and other results support the hypothesis that the reduction of tellurite generates superoxide anions and that the primary targets of superoxide damage in E . coli are enzymes with iron-sulfur clusters . Bacterial rRNA Genes Associated with Soil Suppressiveness against the Plant-Parasitic Nematode Heterodera schachtii. Bei Yin, 2003.The goal of this study was to identify bacteria involved in soil suppressiveness against the plant-parasitic nematode Heterodera schachtii . Since H . schachtii cysts isolated from the suppressive soil can transfer this beneficial property to nonsuppressive soils, analysis of the cyst-associated microorganisms should lead to the identification of the causal organisms . Our experimental approach was to identify bacterial rRNA genes (rDNA) associated with H . schachtii cysts obtained from soil mixtures with various levels of suppressiveness . We hypothesized that we would be able to identify bacteria involved in the suppressiveness by correlating population shifts with differing levels of suppressiveness . Soil treatments containing different amounts of suppressive and fumigation-induced nonsuppressive soils exhibited various levels of suppressiveness after two nematode generations . The 10%-suppressive-soil treatment contained numbers of eggs per gram of soil similar to those of the 100%-suppressive-soil treatment, indicating that the suppressive factor(s) had been transferred . Bacterial rDNA associated with H . schachtii cysts were identified using a culture-independent method termed oligonucleotide fingerprinting of rRNA genes . Bacteria from five major taxonomic groups (Actinobacteria, Cytophaga-Flexibacter-Bacteroides,  -Proteobacteria, ß-Proteobacteria, and
 -Proteobacteria) were identified . Three bacterial rDNA groups contained clones that were more prevalent in the highly suppressive soil treatments than in the less suppressive treatments, indicating a potential involvement in the H . schachtii suppressiveness . When these three groups were examined with specific PCR analyses performed on H . schachtii cysts that developed in soils treated with three biocidal compounds, only one bacterial rDNA group with moderate to high sequence identity to rDNA from several Rhizobium species and uncultured
-proteobacterial clones was consistently associated with the highly suppressive treatments . A quantitative PCR analysis confirmed the association of this Rhizobium-like rDNA group with the H . schachtii suppressiveness .
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