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Transcriptional Regulation of the Staphylococcus aureus Thioredoxin and Thioredoxin Reductase Genes in Response to Oxygen and Disulfide Stress. Orit Uziel, 2004.In this report we describe the cloning, organization, and promoter analysis of the Staphylococcus aureus thioredoxin (trxA) and thioredoxin reductase (trxB) genes and their transcription in response to changes in oxygen concentration and to oxidative stress compounds . Northern analysis showed that the S . aureus trxA and trxB genes were transcribed equally well in aerobic and anaerobic conditions . Several oxidative stress compounds were found to rapidly induce transcription of the trxA and trxB genes . The most pronounced effects were seen with diamide, a thiol-specific oxidant that promotes disulfide bond formation; menadione, a redox cycling agent; and  -butyl
hydroperoxide, an organic peroxide . In each case the induction was
independent of the general stress sigma factor
 B .
These studies show that the S . aureus trxA and trxB
genes are upregulated following exposure to these oxidative stress
agents, resulting in increased disulfide bond formation . In contrast,
no effect of hydrogen peroxide on induction of the trxA and
trxB genes was seen . We also show that the S . aureus
thioredoxin reductase appears to be essential for growth . This
observation, coupled with structural differences between the
bacterial and mammalian thioredoxin reductases, suggests that it may
serve as a target for the development of new antimicrobials .
Acquisition of an Agrobacterium Ri Plasmid and Pathogenicity by Other  -Proteobacteria in Cucumber and Tomato Crops Affected by Root Mat.S. A. Weller, 2004.Root mat of cucumbers and tomatoes has previously been shown to be caused by Agrobacterium radiobacter strains harboring a root-inducing Ri plasmid (pRi) . Nine other pRi-harboring -Proteobacteria have subsequently been isolated from root mat-infected crops . Fatty acid profiling and partial 16S rRNA sequence analysis identified three of these strains as being in the genus Ochrobactrum, five as being in the genus Rhizobium, and one as being in the genus Sinorhizobium . An in vitro pathogenicity test involving inoculation of cucumber cotyledons was developed . All pRi-harboring
-Proteobacteria induced typical root mat symptoms from the cotyledons . Average transformation rates for rhizogenic Ochrobactrum (46%) and Rhizobium (44%) strains were lower than those observed for rhizogenic A . radiobacter strains (64%) . However, individual strains from these three genera all had transformation rates comparable to those observed from cotyledons inoculated with a rhizogenic Sinorhizobium strain (75%) .
Effect of Escherichia coli Morphogene bolA on Biofilms. Helena L. A. Vieira, 2004. Structural Maintenance of Chromosomes Protein of Bacillus subtilis Affects Supercoiling In Vivo. Janet C. Lindow, 2002.Structural maintenance of chromosomes (SMC) proteins are found in nearly all organisms . Members of this protein family are involved in chromosome condensation and sister chromatid cohesion . Bacillus subtilis SMC protein (BsSMC) plays a role in chromosome organization and partitioning . To better understand the function of BsSMC, we studied the effects of an smc null mutation on DNA supercoiling in vivo . We found that an smc null mutant was hypersensitive to the DNA gyrase inhibitors coumermycin A1 and norfloxacin . Furthermore, depleting cells of topoisomerase I substantially suppressed the partitioning defect of an smc null mutant . Plasmid DNA isolated from an smc null mutant was more negatively supercoiled than that from wild-type cells . In vivo cross-linking experiments indicated that BsSMC was bound to the plasmid . Our results indicate that BsSMC affects supercoiling in vivo, most likely by constraining positive supercoils, an activity which contributes to chromosome compaction and organization . Extensive Variation in the O-Antigen Gene Cluster within One Salmonella enterica Serogroup Reveals an Unexpected Complex History. Lei Wang, 2002.The 46 serogroups of Salmonella enterica have different O-antigens, and each is thought to have a specific form of the O-antigen cluster . Comparison of the 145 serovars of serogroup B revealed much more intraserogroup genetic diversity than expected . The O27 factor, due to an  1-6 linkage between O units in place of the more common
1-2 linkage and previously thought to be due to a converting bacteriophage, is now shown to be due to a wzy(1-6) gene located within the major gene cluster . Surprisingly a remnant of this gene in all O27- serovars shows that the ancestor was O27+ . There are six distinct gene cluster forms, five apparently derived by a series of deletions and one by an insertion from an ancestral O27+ form present in 57 serovars . The history of the gene cluster and movement between subspecies I and II can be traced . Two of the derivative forms still have a functional wzy(1-6) gene, while in three it has been inactivated by deletion or insertion . Two of the forms lacking a functional wzy(1-6) gene have the wzy(1-2) gene first described for strain LT2 as rfc, whereas for the third the wzy gene has not been located .
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