Burkholderia humptydooensis sp. nov., a New Species Related to Burkholderia thailandensis and the Fifth Member of the Burkholderia pseudomallei Complex

Abstract

During routine screening for <i>Burkholderia pseudomallei</i> from water wells in northern Australia in areas where it is endemic, Gram-negative bacteria (strains MSMB43^T, MSMB121, and MSMB122) with a similar morphology and biochemical pattern to <i>B. pseudomallei</i> and <i>B. thailandensis</i> were coisolated with <i>B. pseudomallei</i> on Ashdown's selective agar. To determine the exact taxonomic position of these strains and to distinguish them from <i>B. pseudomallei</i> and <i>B. thailandensis</i>, they were subjected to a series of phenotypic and molecular analyses. Biochemical and fatty acid methyl ester analysis was unable to distinguish <i>B. humptydooensis</i> sp. nov. from closely related species. With matrix-assisted laser desorption ionization-time of flight analysis, all isolates grouped together in a cluster separate from other <i>Burkholderia</i> spp. 16S rRNA and <i>recA</i> sequence analyses demonstrated phylogenetic placement for <i>B. humptydooensis</i> sp. nov. in a novel clade within the <i>B. pseudomallei</i> group. Multilocus sequence typing (MLST) analysis of the three isolates in comparison with MLST data from 3,340 <i>B. pseudomallei</i> strains and related taxa revealed a new sequence type (ST318). Genome-to-genome distance calculations and the average nucleotide identity of all isolates to both <i>B. thailandensis</i> and <i>B. pseudomallei</i>, based on whole-genome sequences, also confirmed <i>B. humptydooensis</i> sp. nov. as a novel <i>Burkholderia</i> species within the <i>B. pseudomallei</i> complex. Molecular analyses clearly demonstrated that strains MSMB43^T, MSMB121, and MSMB122 belong to a novel <i>Burkholderia</i> species for which the name <i>Burkholderia humptydooensis</i> sp. nov. is proposed, with the type strain MSMB43^T (American Type Culture Collection BAA-2767; Belgian Co-ordinated Collections of Microorganisms LMG 29471; DDBJ accession numbers CP013380 to CP013382).<b>IMPORTANCE</b><i>Burkholderia pseudomallei</i> is a soil-dwelling bacterium and the causative agent of melioidosis. The genus <i>Burkholderia</i> consists of a diverse group of species, with the closest relatives of <i>B. pseudomallei</i> referred to as the <i>B. pseudomallei</i> complex. A proposed novel species, <i>B. humptydooensis</i> sp. nov., was isolated from a bore water sample from the Northern Territory in Australia. <i>B. humptydooensis</i> sp. nov. is phylogenetically distinct from <i>B. pseudomallei</i> and other members of the <i>B. pseudomallei</i> complex, making it the fifth member of this important group of bacteria.