Choline Catabolism in Burkholderia thailandensis Is Regulated by Multiple Glutamine Amidotransferase 1-Containing AraC Family Transcriptional Regulators

Burkholderia thailandensis is a soil-dwelling bacterium that shares many metabolic pathways with the ecologically similar, but evolutionarily distant,Pseudomonas aeruginosa . Among the diverse nutrients it can utilize is choline, metabolizable to the osmoprotectant glycine betaine and subsequently catabolized as a source of carbon and nitrogen, similar toP. aeruginosa . Orthologs of genes in the choline catabolic pathway in these two bacteria showed distinct differences in gene arrangement as well as an additional orthologous transcriptional regulator inB. thailandensis . In this study, we showed that multiple glutamine amidotransferase 1 (GATase 1)-containing AraC family transcription regulators (GATRs) are involved in regulation of theB. thailandensis choline catabolic pathway (gbdR1 ,gbdR2 , andsouR ). Using genetic analyses and sequencing the transcriptome in the presence and absence of choline, we identified the likely regulons ofgbdR1 (BTH_II1869 ) andgbdR2 (BTH_II0968 ). We also identified a functional ortholog forP. aeruginosa souR , a GATR that regulates the metabolism of sarcosine to glycine. GbdR1 is absolutely required for expression of the choline catabolic locus, similar toP. aeruginosa GbdR, while GbdR2 is important to increase expression of the catabolic locus. Additionally, theB. thailandensis SouR ortholog (BTH_II0994 ) is required for catabolism of choline and its metabolites as carbon sources, whereas inP. aeruginosa , SouR function can by bypassed by GbdR. The strategy employed byB. thailandensis represents a distinct regulatory solution to control choline catabolism and thus provides both an evolutionary counterpoint and an experimental system to analyze the acquisition and regulation of this pathway during environmental growth and infection.IMPORTANCE Many proteobacteria that occupy similar environmental niches have horizontally acquired orthologous genes for metabolism of compounds useful in their shared environment. The arrangement and differential regulation of these components can help us understand both the evolution of these systems and the potential roles these pathways have in the biology of each bacterium. Here, we describe the transcriptome response ofBurkholderia thailandensis to the eukaryote-enriched molecule choline, identify the regulatory pathway governing choline catabolism, and compare the pathway to that previously described forPseudomonas aeruginosa . These data support a multitiered regulatory network inB. thailandensis , with conserved orthologs in the select agentsBurkholderia pseudomallei andBurkholderia mallei , as well as the opportunistic lung pathogens in theBurkholderia cepacia clade.