Characterization of Three Types of Quorum-Sensing Mutants in Burkholderia glumae Strains Isolated in Japan

Abstract

Quorum sensing (QS) has been believed to be essential for the production of virulence factor such as toxoflavin, oxalate and the motility in Burkholderia glumae . Two types of QS mutant ( tofI mutant) were recently reported in geographically different isolates of B. glumae . The tofI mutant derived from B. glumae BGR1 isolated in Korea had lost toxoflavin production but not the one derived from B. glumae 336gr-1 isolated in the United States. In the present study, we generated tofI mutants from 14 different B. glumae strains isolated in Japan and investigated the QS-regulated phenotypes. All tofI mutants failed to produce N -acyl- L -homoserine lactones. However, tofI mutants from 11 out of 14 strains (Group I) retained toxoflavin productivity both on a solid and in a liquid medium like B. glumae 336gr-1 tofI mutant, whereas those from 2 strains (Group II) lost toxoflavin productivity both on a solid and in a liquid medium similar to B. glumae BGR1 tofI mutant. The other strain (Group III) showed novel phenotype because toxoflavin production was observed only on a solid medium. Furthermore, Group II tofI mutants lost oxalate productivity and exhibited a severe reduction in motility while Group I tofI mutants slightly produced oxalate and showed higher motility than Group II tofI mutants. These data suggest that the difference between Group I and II is not limited to toxoflavin production but also observed other QS-regulated functions. On the other hand, R1-types of morphological mutants frequently emerge from S-type colonies during the subculture for B. glumae (Tsushima et al., 1991). This study revealed that Group I wild-type strains displayed the S-type morphology and those of Group II showed the R1-type morphology. The results suggest that colony type is involved in the QS-regulated functions of Group I and II tofI mutants.