Diversities in Virulence, Antifungal Activity, Pigmentation and DNA Fingerprint among Strains of Burkholderia glumae

Abstract

Burkholderia glumae is the primary causal agent of bacterial panicle blight of rice. In this study, 11 naturally avirulent and nine virulent strains of B. glumae native to the southern United States were characterized in terms of virulence in rice and onion, toxofalvin production, antifungal activity, pigmentation and genomic structure. Virulence of B. glumae strains on rice panicles was highly correlated to virulence on onion bulb scales, suggesting that onion bulb can be a convenient alternative host system to efficiently determine the virulence of B. glumae strains. Production of toxoflavin, the phytotoxin that functions as a major virulence factor, was closely associated with the virulence phenotypes of B. glumae strains in rice. Some strains of B. glumae showed various levels of antifungal activity against Rhizoctonia solani, the causal agent of sheath blight, and pigmentation phenotypes on casamino acid-peptone-glucose (CPG) agar plates regardless of their virulence traits. Purple and yellow-green pigments were partially purified from a pigmenting strain of B. glumae, 411gr-6, and the purple pigment fraction showed a strong antifungal activity against Collectotrichum orbiculare. Genetic variations were detected among the B. glumae strains from DNA fingerprinting analyses by repetitive element sequence-based PCR (rep-PCR) for BOX-A1R-based repetitive extragenic palindromic (BOX) or enterobacterial repetitive intergenic consensus (ERIC) sequences of bacteria; and close genetic relatedness among virulent but pigment-deficient strains were revealed by clustering analyses of DNA fingerprints from BOX-and ERIC-PCR.

Dissection of Quorum-Sensing Genes in Burkholderia glumae Reveals Non-Canonical Regulation and the New Regulatory Gene tofM for Toxoflavin Production

“…Similar results were observed in tests with other types of solid media, including King’s B agar [24] (data not shown). In an onion assay established to indirectly determine the virulence of B. glumae [23], LSUPB145 and LSUPB169, but not LSUPB139, were able to cause comparable or larger maceration symptoms on onion bulb scales in comparison with the wild type (Figure 5B). Inoculums prepared from the cultures in LB broth and LB agar showed similar results (data not shown).…”

“…The onion assay system that was previously used to determine the virulence of Burkholderia cenocepacia [22] and B. glumae [18], [23] was adopted in this study with minor modifications. Briefly, the fleshy scales of yellow onions were cut into pieces (∼2×4 cm) with a sterile razorblade and a 2 mm-slit was made in the center of each onion piece with a sterile micropipette tip.…”

“…The inoculated onion scales were incubated in a moist chamber at 30°C for 72 h. The virulence level of each B. glumae strain was assessed by measuring the area of maceration on each onion scale. Virulence of B. glumae strains in rice was tested following a previously established method [23].…”

The roles of the shikimate pathway genes, aroA and aroB, in virulence, growth and UV tolerance of Burkholderia glumae strain 411gr‐6

“…D) (Steinrucken and Amrhein, ). Growth of B. glumae 336gr‐1, a pigment‐deficient wild‐type strain (Karki et al ., ), was also inhibited by glyphosate in M9 medium, like B. glumae 411gr‐6 (Fig. D), suggesting that a functional shikimate pathway is required for the growth of B. glumae in minimal medium.…”

Structural elucidation and antimicrobial activity of new phencomycin derivatives isolated from Burkholderia glumae strain 411gr-6

“…They comprise a large group of nitrogencontaining heterocyclic compounds with different chemical and physical properties dependent upon the type and position of the functional groups present. 4 In the course of our investigation on the antimicrobial pigments produced by Burkholderia glumae strain 411gr-6, 5 we identified phencomycin 6 (a phenazine with two substituents, a carboxyl and a carbomethoxy group; Figure 1) and its new derivatives. Here, we report the purification, structural elucidation and antimicrobial properties of 4-hydroxyphencomycin (1) and 5,10-dihydro-4,9-dihydroxyphencomycin methyl ester (2; Figure 2).…”