Amino Acid Substitutions in GyrA ofBurkholderia glumaeAre Implicated in Not Only Oxolinic Acid Resistance but Also Fitness on Rice Plants

Abstract

Oxolinic acid (OA) resistance in field isolates of Burkholderia glumae, a causal agent of bacterial grain rot, is dependent on an amino acid substitution at position 83 in GyrA (GyrA83). In the present study, among spontaneous in vitro mutants from the OA-sensitive B. glumae strain Pg-10, we selected OA-resistant mutants that emerged at a rate of 5.7 ؋ 10 ؊10 . Nucleotide sequence analysis of the quinolone resistance-determining region in GyrA showed that Gly81Cys, Gly81Asp, Asp82Gly, Ser83Arg, Asp87Gly, and Asp87Asn are observed in these OA-resistant mutants. The introduction of each amino acid substitution into Pg-10 resulted in OA resistance, similar to what was observed for mutants with the responsible amino acid substitution. In vitro growth of recombinants with Asp82Gly was delayed significantly compared to that of Pg-10; however, that of the other recombinants did not differ significantly. The inoculation of each recombinant into rice spikelets did not result in disease. In inoculated rice spikelets, recombinants with Ser83Arg grew less than Pg-10 during flowering, and growth of the other recombinants was reduced significantly. On the other hand, the reduced growth of recombinants with Ser83Arg in spikelets was compensated for under OA treatment, resulting in disease. These results suggest that amino acid substitutions in GyrA of B. glumae are implicated in not only OA resistance but also fitness on rice plants. Therefore, GyrA83 substitution is thought to be responsible for OA resistance in B. glumae field isolates.

Multiple endogenous seed-born bacteria recovered rice growth disruption caused by Burkholderia glumae

“…Other major means for the control of B. glumae in Japan 12 is seed treatment with oxolinic acid, a quinoline derivative. However, the occurrence of strains naturally resistant to oxolinic acid has been a serious limitation to this method of disease control 12 , 13 .…”

Evaluation of major Japanese rice cultivars for resistance to bacterial grain rot caused by <i>Burkholderia glumae</i> and identification of standard cultivars for resistance

“…Seed treatment with oxolinic acid, a quinoline derivative, is a major means of bacterial disease control in Japan ( Hikichi 1993a , 1993b , Hikichi et al 1989 ). However, the occurrence of BGR strains naturally resistant to oxolinic acid has been a serious limitation to this method ( Hikichi et al 2001 , Maeda et al 2004 , 2007 ). On the other hand, seed disinfection in hot water (for example, 60°C for 10 min) has been established ( Hayasaka et al 2001 ).…”

Identification of sRNA mediated responses to nutrient depletion in Burkholderia pseudomallei

“…Burkholderia species, such as Burkholderia pseudomallei , Burkholderia mallei and Burkholderia cepacia are known to cause melioidoisis 2 , 3 , glanders 4 and pulmonary infections in cystic fibrosis patients 5 , 6 , respectively. Others such as Burkholderia plantarii , Burkholderia glumae and Burkholderia gladioli have been reported to be pathogens of rice plant 7 . Several species such as Burkholderia vietnamiensis , Burkholderia brasiliensis , Burkholderia phymatum and Burkholderia phytofirmans sp .…”