Modest Changes in Extracellular pH Impose Metabolic and Envelope Remodeling in Burkholderia thailandensis.

Burkholderia thailandensis is a commonly used surrogate for pathogenic Burkholderia species, yet how it adapts to changes in extracellular pH remains poorly characterized. Using quantitative mass spectrometry, we report here the relative proteomes for cells exposed to a change in pH from 7.0 to either 6.0 or 8.0, conditions that may be encountered in the rhizosphere. Acute exposure to mildly acidic conditions resulted in four proteins being depleted while four accumulated based on an absolute log2-fold change of 0.4. By comparison, a transition to mildly alkaline conditions resulted in accumulation of 13 proteins and depletion of 14. Exposure to both pH 6.0 and pH 8.0 resulted in an overall reduction in the pathways linked to ribosome, flagellar assembly, and β-lactam resistance. Consistent with the observed pathway changes, both surface motility and resistance to certain β-lactams were greatly reduced at pH 6.0 and 8.0 compared to pH 7.0. Transcriptome changes at pH 8.0 primarily included global downregulation of genes associated with flagellar motility and chemotaxis, while genes encoding secondary metabolite biosynthetic enzymes were markedly upregulated. Taken together, our data afford insight into how B. thailandensis responds to physiologically relevant pH changes to achieve optimal niche adaptation, survival, and competitive fitness.