Role of metAB in Methionine Metabolism and Optimal Chicken Colonization in Campylobacter jejuni

is a zoonotic pathogen and is one of the leading causes of human gastroenteritis worldwide. IA3902 (representative of the sheep abortion clone) is genetically similar to W7 (representative of strain type NCTC 11168); however, there are significant differences in the ability of mutants of these strains to colonize chickens. LuxS is essential for the activated methyl cycle and generates homocysteine for conversion to l-methionine. Comparative genomics identified differential distribution of the genes and , which function to convert homoserine for downstream production of l-methionine, between IA3902 and W7, which could enable a secondary pathway for l-methionine biosynthesis in a W7 Δ but not in an IA3902 Δ strain. To test the hypothesis that the genes and contribute to l-methionine production and chicken colonization by , we constructed two mutants for phenotypic comparison, the W7 Δ Δ and IA3902 Δ :: mutants. Quantitative reverse transcription-PCR and tandem mass spectrometry protein analysis were used to validate MetAB transcription and translation as present in the IA3902 Δ :: mutant and absent in the W7 Δ Δ mutant. Time-resolved fluorescence resonance energy transfer fluorescence assays demonstrated that l-methionine and -adenosyl methionine concentrations decreased in the W7 Δ Δ mutant and increased in the IA3902 Δ :: mutant. Assessment of chicken colonization revealed that the IA3902 Δ :: strain partially rescued the colonization defect of the IA3902 Δ strain, while the W7 Δ Δ strain showed significantly decreased colonization compared to that of the wild-type and the W7 Δ strain. These results indicate that the ability to maintain l-methionine production , conferred by and in the absence of , is critical for normal chicken colonization by .