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LasR, a Transcriptional Activator of Pseudomonas aeruginosa Virulence Genes, Functions as a Multimer. Pattarachai Kiratisin, 2002.The Pseudomonas aeruginosa LasR protein functions in concert with N-3-oxo-dodecanoyl-L-homoserine lactone (3O-C12-HSL) to coordinate the expression of target genes, including many genes that encode virulence factors, with cell density . We used a LexA-based protein interaction assay to demonstrate that LasR forms multimers only when 3O-C12-HSL is present . A series of LasR molecules containing internal deletions or substitutions in single, conserved amino acid residues indicated that the N-terminal portion of LasR is required for multimerization . Studies performed with these mutant versions of LasR demonstrated that the ability of LasR to multimerize correlates with its ability to function as a transcriptional activator of lasI, a gene known to be tightly regulated by the LasR-3O-C12-HSL regulatory system . A LasR molecule that carries a C-terminal deletion can function as a dominant-negative mutant in P . aeruginosa, as shown by its ability to decrease expression of lasB, another LasR-3O-C12-HSL target gene . Taken together, our data strongly support the hypothesis that LasR functions as a multimer in vivo . Inactivation of ompR Promotes Precocious Swarming and flhDC Expression in Xenorhabdus nematophila. Dong-jin Kim, 2003.The response regulator OmpR is involved in numerous adaptive responses to environmental challenges . The role that OmpR plays in swarming behavior and swarm-cell differentiation in the symbiotic-pathogenic bacterium Xenorhabdus nematophila was examined in this study . Swarming began 4 h sooner in an ompR mutant strain than in wild-type cells . Precocious swarming was correlated with elevated expression of fliC, early flagellation, and cell elongation . The level of flhDC mRNA was elevated during the early period of swarming in the ompR strain relative to the level in the wild type . These findings show that OmpR is involved in the temporal regulation of flhDC expression and flagellum production and demonstrate that this response regulator plays a role in the swarming behavior of X . nematophila . Exogenous Glutathione Completes the Defense against Oxidative Stress in Haemophilus influenzae. Bjorn Vergauwen, 2003.Since they are equipped with several strategies by which they evade the antimicrobial defense of host macrophages, it is surprising that members of the genus Haemophilus appear to be deficient in common antioxidant systems that are well established to protect prokaryotes against oxidative stress . Among others, no genetic evidence for glutathione (  -Glu-Cys-Gly) (GSH) biosynthesis or for alkyl hydroperoxide reduction (e.g., the Ahp system characteristic or enteric bacteria) is apparent from the Haemophilus influenzae Rd genome sequence, suggesting that the organism relies on alternative systems to maintain redox homeostasis or to reduce small alkyl hydroperoxides . In this report we address this apparent paradox for the nontypeable H . influenzae type strain NCTC 8143 . Instead of biosynthesis, we could show that this strain acquires GSH by importing the thiol tripeptide from the growth medium . Although such GSH accumulation had no effect on growth rates, the presence of cellular GSH protected against methylglyoxal, tert-butyl hydroperoxide (t-BuOOH), and S-nitrosoglutathione toxicity and regulated the activity of certain antioxidant enzymes . H . influenzae NCTC 8143 extracts were shown to contain GSH-dependent peroxidase activity with t-BuOOH as the peroxide substrate . The GSH-mediated protection against t-BuOOH stress is most probably catalyzed by the product of open reading frame HI0572 (Prx/Grx), which we isolated from a genomic DNA fragment that confers wild-type resistance to t-BuOOH toxicity in the Ahp-negative Escherichia coli strain TA4315 and that introduces GSH-dependent alkyl hydroperoxide reductase activity into naturally GSH peroxidase-negative E . coli . Finally, we demonstrated that cysteine is an essential amino acid for growth and that cystine, GSH, glutathione amide, and cysteinylglycine can be catabolized in order to complement cysteine deficiency .
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