Reassessment of the taxonomic position of Burkholderia andropogonis and description of Robbsia andropogonis gen. nov., comb. nov.

The phylogenetic classification of the species Burkholderia andropogonis within the Burkholderia genus was reassessed using 16S rRNA gene phylogenetic analysis and multilocus sequence analysis (MLSA). Both phylogenetic trees revealed two main groups, named A and B, strongly supported by high bootstrap values (100%). Group A encompassed all of the Burkholderia species complex, whi.le Group B only comprised B. andropogonis species, with low percentage similarities with other species of the genus, from 92 to 95% for 16S rRNA gene sequences and 83% for conserved gene sequences. Average nucleotide identity (ANI), tetranucleotide signature frequency, and percentage of conserved proteins POCP analyses were also carried out, and in the three analyses B. andropogonis showed lower values when compared to the other Burkholderia species complex, near 71% for ANI, from 0.484 to 0.724 for tetranucleotide signature frequency, and around 50% for POCP, reinforcing the distance observed in the phylogenetic analyses. Our findings provide an important insight into the taxonomy of B. andropogonis. It is clear from the results that this bacterial species exhibits genotypic differences and represents a new genus described herein as Robbsia andropogonis gen. nov., comb. nov.

A simplified subtractive hybridization protocol used to isolate DNA sequences specific to Xylella fastidiosa.

A simplified protocol of subtractive hybridization based on the technique of L. M. Kunkel, A. P. Monaco, W. Middlesworth, H. D. Ochs & S. A. Latt (1985, Proc Natl Acad Sci USA, 82, 4778-4782) was used to obtain DNA sequences specific to Xylella fastidiosa isolated from diseased citrus plants. As a driver, DNA extracted from bacteria showing different degrees of relatedness was used: Xy. fastidiosa 788 isolated from another host (plum), Xanthomonas campestris pv. campestris and Burkholderia gladioli strains. A DNA fragment, f14, showing no hybridization to the driver DNA, was used as a probe specific to Xy. fastidiosa from citrus and oleander. This fragment was sequenced and the predicted protein showed 40% similarity to the central region of flagellin of Escherichia coli serotypes H1 and H12. A pair of internal primers (f14-1 and f14-2) was designed for amplification of Xy. fastidiosa DNA. These primers detected Xy. fastidiosa strains isolated from citrus and oleander and yielded an amplification product of about 600 bp. They were also able to detect the bacteria in extracts from citrus plants with or without symptoms of disease. No amplification reaction was obtained using DNA extracted from other species and pathovars of Xanthomonas, Pseudomonas cichorii, Erwinia carotovora, Agrobacterium tumefaciens and phytopathogens of citrus (Xanthomonas axonopodis pv. citri) and coffee (Burkholderia andropogonis, P. cichorii, Pseudomonas syringae pv. garcae). The isolation of a DNA fragment specific to Xy. fastidiosa from citrus showed that the simplified protocol of subtractive hybridization used in this work is potentially applicable to other micro-organisms.