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Implications of Amino Acid Substitutions in GyrA at Position 83 in Terms of Oxolinic Acid Resistance in Field Isolates of Burkholderia glumae, a Causal Agent of Bacterial Seedling Rot and Grain Rot of Rice. Yukiko Maeda, 2004.Oxolinic acid (OA), a quinolone, inhibits the activity of DNA gyrase composed of GyrA and GyrB and shows antibacterial activity against Burkholderia glumae . Since B . glumae causes bacterial seedling rot and grain rot of rice, both of which are devastating diseases, the emergence of OA-resistant bacteria has important implications on rice cultivation in Japan . Based on the MIC of OA, 35 B . glumae field isolates isolated from rice seedlings grown from OA-treated seeds in Japan were divided into sensitive isolates (OSs; 0.5 µg/ml), moderately resistant isolates (MRs; 50 µg/ml), and highly resistant isolates (HRs;  100 µg/ml) . Recombination with gyrA of an OS, Pg-10, led MRs and HRs to become OA susceptible, suggesting that gyrA mutations are involved in the OA resistance of field isolates . The amino acid at position 83 in the GyrA of all OSs was Ser, but in all MRs and HRs it was Arg and Ile, respectively . Ser83Arg and Ser83Ile substitutions in the GyrA of an OS, Pg-10, resulted in moderate and high OA resistance, respectively . Moreover, Arg83Ser and Ile83Ser substitutions in the GyrA of MRs and HRs, respectively, resulted in susceptibility to OA . These results suggest that Ser83Arg and Ser83Ile substitutions in GyrA are commonly responsible for resistance to OA in B . glumae field isolates .
Identification of GtgE, a Novel Virulence Factor Encoded on the Gifsy-2 Bacteriophage of Salmonella enterica Serovar Typhimurium. Theresa D. Ho, 2002.The Gifsy-2 temperate bacteriophage of Salmonella enterica serovar Typhimurium contributes significantly to the pathogenicity of strains that carry it as a prophage . Previous studies have shown that Gifsy-2 encodes SodCI, a periplasmic Cu/Zn superoxide dismutase, and at least one additional virulence factor . Gifsy-2 encodes a Salmonella pathogenicity island 2 type III secreted effector protein . Sequence analysis of the Gifsy-2 genome also identifies several open reading frames with homology to those of known virulence genes . However, we found that null mutations in these genes did not individually have a significant effect on the ability of S . enterica serovar Typhimurium to establish a systemic infection in mice . Using deletion analysis, we have identified a gene, gtgE, which is necessary for the full virulence of S . enterica serovar Typhimurium Gifsy-2 lysogens . Together, GtgE and SodCI account for the contribution of Gifsy-2 to S . enterica serovar Typhimurium virulence in the murine model . Identification of an Acetoacetyl Coenzyme A Synthetase-Dependent Pathway for Utilization of L-(+)-3-Hydroxybutyrate in Sinorhizobium meliloti. Punita Aneja, 2002.D-(-)-3-Hydroxybutyrate (DHB), the immediate depolymerization product of the intracellular carbon store poly-3-hydroxybutyrate (PHB), is oxidized by the enzyme 3-hydroxybutyrate dehydrogenase to acetoacetate (AA) in the PHB degradation pathway . Externally supplied DHB can serve as a sole source of carbon and energy to support the growth of Sinorhizobium meliloti . In contrast, wild-type S . meliloti is not able to utilize the L-(+) isomer of 3-hydroxybutyrate (LHB) as a sole source of carbon and energy . In this study, we show that overexpression of the S . meliloti acsA2 gene, encoding acetoacetyl coenzyme A (acetoacetyl-CoA) synthetase, confers LHB utilization ability, and this is accompanied by novel LHB-CoA synthetase activity . Kinetics studies with the purified AcsA2 protein confirmed its ability to utilize both AA and LHB as substrates and showed that the affinity of the enzyme for LHB was clearly lower than that for AA . These results thus provide direct evidence for the LHB-CoA synthetase activity of the AcsA2 protein and demonstrate that the LHB utilization pathway in S . meliloti is AcsA2 dependent . Improved Adaptation to Cold-Shock, Stationary-Phase, and Freezing Stresses in Lactobacillus plantarum Overproducing Cold-Shock Proteins. Sylviane Derzelle, 2003.We have investigated the effect of overproducing each of the three cold shock proteins (CspL, CspP, and CspC) in the mesophilic lactic acid bacterium Lactobacillus plantarum NC8 . CspL overproduction transiently alleviated the reduction in growth rate triggered by exposing exponentially growing cells to cold shock (8°C), suggesting that CspL is involved in cold adaptation . The strain overproducing CspC resumed growth more rapidly when stationary-phase cultures were diluted into fresh medium, indicating a role in the adaptation and recovery of nutritionally deprived cells . Overproduction of CspP led to an enhanced capacity to survive freezing .
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