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The Global Regulator Genes from Biocontrol Strain Serratia plymuthica IC1270: Cloning, Sequencing, and Functional Studies. Marianna Ovadis, 2004.The biocontrol activity of various fluorescent pseudomonads towards plant-pathogenic fungi is dependent upon the GacA/GacS-type two-component system of global regulators and the RpoS transcription sigma factor . In particular, these components are required for the production of antifungal antibiotics and exoenzymes . To investigate the effects of these global regulators on the expression of biocontrol factors by plant-associated bacteria other than Pseudomonas spp., gacA/gacS and rpoS homologues were cloned from biocontrol strain IC1270 of Serratia plymuthica, which produces a set of antifungal compounds, including chitinolytic enzymes and the antibiotic pyrrolnitrin . The nucleotide and deduced protein sequence alignments of the cloned gacA/gacS-like genes—tentatively designated grrA (global response regulation activator) and grrS (global response regulation sensor) and of the cloned rpoS gene revealed 64 to 93% identity with matching genes and proteins of the enteric bacteria Escherichia coli, Pectobacterium carotovora subsp . carotovora, and Serratia marcescens . grrA, grrS, and rpoS gene replacement mutants of strain IC1270 were deficient in the production of pyrrolnitrin, an exoprotease, and N-acylhomoserine lactone quorum-sensing signal molecules . However, neither mutant appeared to differ from the parental strain in the production of siderophores, and only grrA and grrS mutants were deficient in the production of a 58-kDa endochitinase, representing the involvement of other sigma factors in the regulation of strain IC1270's chitinolytic activity . Compared to the parental strain, the grrA, grrS, and rpoS mutants were markedly less capable of suppressing Rhizoctonia solani and Pythium aphanidermatum under greenhouse conditions, indicating the dependence of strain IC1270's biocontrol property on the GrrA/GrrS and RpoS global regulators . In Vitro and In Vivo Activities of E5700 and ER-119884, Two Novel Orally Active Squalene Synthase Inhibitors, against Trypanosoma cruzi. Julio A. Urbina, 2004.Chagas' disease is a serious public health problem in Latin America, and no treatment is available for the prevalent chronic stage . Its causative agent, Trypanosoma cruzi, requires specific endogenous sterols for survival, and we have recently demonstrated that squalene synthase (SQS) is a promising target for antiparasitic chemotherapy . E5700 and ER-119884 are quinuclidine-based inhibitors of mammalian SQS that are currently in development as cholesterol- and triglyceride-lowering agents in humans . These compounds were found to be potent noncompetitive or mixed-type inhibitors of T . cruzi SQS with Ki values in the low nanomolar to subnanomolar range in the absence or presence of 20 µM inorganic pyrophosphate . The antiproliferative 50% inhibitory concentrations of the compounds against extracellular epimastigotes and intracellular amastigotes were ca . 10 nM and 0.4 to 1.6 nM, respectively, with no effects on host cells . When treated with these compounds at the MIC, all of the parasite's sterols disappeared from the parasite cells . In vivo studies indicated that E5700 was able to provide full protection against death and completely arrested the development of parasitemia when given at a concentration of 50 mg/kg of body weight/day for 30 days, while ER-119884 provided only partial protection . This is the first report of an orally active SQS inhibitor that is capable of providing complete protection against fulminant, acute Chagas' disease . Osmotic Stress Leads to Decreased Intracellular pH of Listeria monocytogenes as Determined by Fluorescence Ratio-Imaging Microscopy. Weihuan Fang, 2004.Intracellular pH (pHi) of Listeria monocytogenes was determined after exposure to NaCl or sorbitol in liquid and solid media (agar) . Both compounds decreased pHi, and recovery on solid medium was impaired compared to that in liquid medium . N,N'-dicyclohexylcarbodiimide abolished pHi recovery, and lowering aw with glycerol showed no effect on pHi . Colonization of Vitis vinifera by a Green Fluorescence Protein-Labeled, gfp-Marked Strain of Xylophilus ampelinus, the Causal Agent of Bacterial Necrosis of Grapevine. Sophie Grall, 2003.The dynamics of Xylophilus ampelinus were studied in Vitis vinifera cv . Ugni blanc using gfp-marked bacterial strains to evaluate the relative importance of epiphytic and endophytic phases of plant colonization in disease development . Currently, bacterial necrosis of grapevine is of economic importance in vineyards in three regions in France: the Cognac, Armagnac, and Die areas . This disease is responsible for progressive destruction of vine shoots, leading to their death . We constructed gfp-marked strains of the CFBP2098 strain of X . ampelinus for histological studies . We studied the colonization of young plants of V . vinifera cv . Ugni blanc by X . ampelinus after three types of artificial contamination in a growth chamber and in a greenhouse . (i) After wounding of the stem and inoculation, the bacteria progressed down to the crown through the xylem vessels, where they organized into biofilms . (ii) When the bacteria were forced into woody cuttings, they rarely colonized the emerging plantlets . Xylem vessels could play a key role in the multiplication and conservation of the bacteria, rather than being a route for plant colonization . (iii) When bacterial suspensions were sprayed onto the plants, bacteria progressed in two directions: both in emerging organs and down to the crown, thus displaying the importance of epiphytic colonization in disease development .
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