Role of metAB in methionine metabolism and optimal chicken colonization in Campylobacter jejuni.

Campylobacter jejuni is a zoonotic pathogen and is one of the leading causes of human gastroenteritis worldwide. C. jejuni IA3902 (representative of the sheep abortion clone) is genetically similar to C. jejuni W7 (representative of strain-type NCTC 11168), however, there are significant differences in the ability of luxS 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 genes metA and metB, 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 W7ΔluxS but not in IA3902ΔluxS. To test the hypothesis that genes metA and metB contribute to L-methionine production and chicken colonization by Campylobacter, we constructed two mutants for phenotypic comparison: W7ΔmetABΔluxS and IA3902ΔluxS::metAB. Quantitative reverse transcription PCR and tandem mass spectrometry protein analysis were used to validate MetAB transcription and translation as present in IA3902ΔluxS::metAB and absent in W7ΔmetABΔluxS. Time-resolved fluorescence resonance energy transfer fluorescence assays demonstrated L-methionine and S-adenosyl methionine concentrations decreased in W7ΔmetABΔluxS and increased in IA3902ΔluxS::metAB. Assessment of chicken colonization revealed that IA3902ΔluxS::metAB partially rescued the colonization defect of IA3902ΔluxS, while W7ΔmetABΔluxS resulted in significantly decreased colonization compared to the wild type and W7ΔluxS. These results indicate that the ability to maintain L-methionine production in vivo, conferred by metA and metB in the absence of luxS, is critical for normal chicken colonization by C. jejuni.