A Burkholderia pseudomallei Colony Variant Necessary for Gastric Colonization

Abstract

Diverse colony morphologies are a hallmark of Burkholderia pseudomallei recovered from infected patients. We observed that stresses that inhibit aerobic respiration shifted populations of B. pseudomallei from the canonical white colony morphotype toward two distinct, reversible, yet relatively stable yellow colony variants (YA and YB). As accumulating evidence supports the importance of B. pseudomallei enteric infection and gastric colonization, we tested the response of yellow variants to hypoxia, acidity, and stomach colonization. Yellow variants exhibited a competitive advantage under hypoxic and acidic conditions and alkalized culture media. The YB variant, although highly attenuated in acute virulence, was the only form capable of colonization and persistence in the murine stomach. The accumulation of extracellular DNA (eDNA) was a characteristic of YB as observed by 4′,6-diamidino-2-phenylindole (DAPI) staining of gastric tissues, as well as in an in vitro stomach model where large amounts of eDNA were produced without cell lysis. Transposon mutagenesis identified a transcriptional regulator (BPSL1887, designated YelR) that when overexpressed produced the yellow phenotype. Deletion of yelR blocked a shift from white to the yellow forms. These data demonstrate that YB is a unique B. pseudomallei pathovariant controlled by YelR that is specifically adapted to the harsh gastric environment and necessary for persistent stomach colonization.

Two stable variants of Burkholderia pseudomallei strain MSHR5848 express broadly divergent in vitro phenotypes associated with their virulence differences

“…Gram stains showed that the Rough variant has the typical safety pin appearance associated with Bp (data not shown), while that characteristic is not as obvious in the Smooth variant ( Fig 1E and 1F ). Also, Smooth, but not Rough, was stained with DNA-binding dye propidium iodide ( Fig 1G–1J ), a finding which supports previous observations that certain mucoid isolates of Bp secrete DNA [ 21 ].…”

“…In addition, five chemicals and eight AMPs were evaluated separately in microtiter plate assays. Inter-experimental variability in Bp responses of the Smooth and Rough variants was observed, as described generally for Bp strains [ 12 , 13 , 21 , 22 ]. The only relatively consistent differences between Smooth and Rough were in sensitivity to the toxic amino acid D-serine and the cationic AMP magainin II [ 53 – 55 ].…”

“…These clones were tested for transition to the other type in the 14 growth conditions described below. The circumstances tested in 1–10 corresponded to those detailed by Wikraiphat et al [ 22 ], 11 was described by Austin et al [ 21 ], 12 and 14 were developed in this study, and 13 was performed according to the conditions depicted by Butt et al [ 41 ]. Six of the Smooth clones tested had been fresh revertants of Rough clone #1 that had been incubated in condition 9 (7 days at 37°C).…”

Phenotypic Variation in the Group A Streptococcus Due to Natural Mutation of the Accessory Protein-Encoding Gene rocA

“…The population of bacteria causing any given infection is most often heterogeneous, and in part this heterogeneity is a consequence of phenotypic variants being selected for during infection ( 14 , 23 , 32 , 36 , 50 – 52 ). Such phenotypic variants can have enhanced abilities to circumvent the host immune response ( 14 ), altered adherence properties ( 53 ), altered metabolism/growth profiles ( 54 ), altered tissue tropism ( 55 ), altered antibiotic resistance profiles ( 56 ), etc. Thus, the whole community of bacteria present during infection needs to be considered when investigating and treating such infections.…”

Characterization of in vitro phenotypes of Burkholderia pseudomallei and Burkholderia mallei strains potentially associated with persistent infection in mice

“…The colony types were associated with in vitro phenotypic differences such as production of alkaline conditions in broth, and evidence suggesting differences in virulence was described. Numerous more recent studies have supported the hypothesis that different colony morphotypes potentially reflect adaptive changes that enhance fitness in a particular environment (Austin et al 2015; Chantratita et al 2007; Rogul and Carr 1972; Tandhavanant et al 2010; Velapatino et al 2012; Wikraiphat et al 2015; Shea, A., unpublished).…”