Burkholderia humptydooensis sp. nov., A Burkholderia thailandensis-Like Species and the Fifth Member of the pseudomallei Complex

Abstract : During routine screening for endemic Burkholderia pseudomallei from water wells in northern Australia, Gram-negative bacteria (strains MSMB43T, MSMB121, and MSMB122) with a similar morphology and biochemical pattern to B. pseudomallei and B. thailandensis were co-isolated with B. pseudomallei on Ashdowns selective agar. To determine the exact taxonomic position of these strains and to distinguish them from B. pseudomallei and B. thailandensis, they were subjected to a series of phenotypic and molecular analyses. Biochemical and fatty acid methyl esters analysis was unable to distinguish B. humptydooensis sp. nov. from closely related species. In MALDI-TOF analysis, all isolates grouped together in a cluster separate from other Burkholderia spp. 16S rRNA and recA sequence analysis demonstrated phylogenetic placement for B. humptydooensis sp. nov. in a novel clade within the B. pseudomallei group. MLST analysis of the three isolates in comparison with MLST data from 3,340 B. pseudomallei strains and related taxa revealed a new sequence type (ST318). Genome to genome distance calculations and average nucleotide identity of all isolates to both B. thailandensis and B. pseudomallei, based on whole genome sequences, also confirmed B. humptydooensis sp. nov. as a novel Burkholderia species within the pseudomallei complex. Molecular analyses clearly demonstrate that strains MSMB43T, MSMB121, and MSMB122 belong to a novel Burkholderia species for which the name Burkholderia humptydooensis sp. nov. is proposed with the type strain MSMB43T (=ATCCXXXXXT; LMGXXXX, CP013380-CP013382). Burkholderia species are abundant and occupy diverse ecological niches, including soil, plants, animals, and humans. Probably the most diverse and environmentally adaptable plant-associated bacteria also belong to the genus Burkholderia (Compant et al., 2008).