Abstract

ABSTRACTDuring routine screening for Burkholderia pseudomallei from water wells in northern Australia in areas where it is endemic, Gram-negative bacteria (strains MSMB43T, MSMB121, and MSMB122) with a similar morphology and biochemical pattern to B. pseudomallei and B. thailandensis were coisolated with B. pseudomallei on Ashdown's 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 ester analysis was unable to distinguish B. humptydooensis 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 Burkholderia spp. 16S rRNA and recA sequence analyses demonstrated phylogenetic placement for B. humptydooensis sp. nov. in a novel clade within the B. pseudomallei group. Multilocus sequence typing (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 the 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 B. pseudomallei complex. Molecular analyses clearly demonstrated 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 (American Type Culture Collection BAA-2767; Belgian Co-ordinated Collections of Microorganisms LMG 29471; DDBJ accession numbers CP013380 to CP013382).IMPORTANCE Burkholderia pseudomallei is a soil-dwelling bacterium and the causative agent of melioidosis. The genus Burkholderia consists of a diverse group of species, with the closest relatives of B. pseudomallei referred to as the B. pseudomallei complex. A proposed novel species, B. humptydooensis sp. nov., was isolated from a bore water sample from the Northern Territory in Australia. B. humptydooensis sp. nov. is phylogenetically distinct from B. pseudomallei and other members of the B. pseudomallei complex, making it the fifth member of this important group of bacteria.

Highlights

  • During routine screening for Burkholderia pseudomallei from water wells in northern Australia in areas where it is endemic, Gram-negative bacteria with a similar morphology and biochemical pattern to B. pseudomallei and B. thailandensis were coisolated with B. pseudomallei on Ashdown’s selective agar

  • Biochemical differentiation of B. humptydooensis sp. nov. from B. pseudomallei and B. thailandensis was possible by screening for the presence of tryptophan, esculin, or the assimilation of arabinose and the assimilation of maltose (Table 1)

  • The high genome-to-genome distance calculation (GGDC) and average nucleotide identity (ANI) values indicate that all of these tested strains belong to a single species, including the proposed B. humptydooensis sp. nov. type strain MSMB43T

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Summary

Introduction

During routine screening for Burkholderia pseudomallei from water wells in northern Australia in areas where it is endemic, Gram-negative bacteria (strains MSMB43T, MSMB121, and MSMB122) with a similar morphology and biochemical pattern to B. pseudomallei and B. thailandensis were coisolated with B. pseudomallei on Ashdown’s selective agar. These closely related species are soil saprophytes and are considered nonpathogenic, a few strains of B. thailandensis and B. oklahomensis have been described as causing clinical infection in humans [12, 15]. Phylogenetic reconstruction of 16S rRNA and recA sequences confirmed genetic proximity to the B. pseudomallei complex and determined that all B. humptydooensis sp.

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