Transposon mutagenesis of Campylobacter jejuni identifies a bipartite energy taxis system required for motility

Campylobacter jejuni constitutes the leading cause of bacterial gastroenter itis in the United States and a major cause of diarrhoea worldwide. Little is known about virulence mechanisms in this organism because of the scarcit y of suitable genetic tools. We have developed an efficient system of in vi tro transposon mutagenesis using a mariner-based transposon and purified ma riner transposase. Through in vitro transposition of C. jejuni chromosomal DNA followed by natural transformation of the transposed DNA, large random transposon mutant libraries consisting of approximate to 16 000 individual mutants were generated. The first genetic screen of C. jejuni using a trans poson-generated mutant library identified 28 mutants defective for flagella r motility, one of the few known virulence determinants of this pathogen. W e developed a second genetic system, which allows for the construction of d efined chromosomal deletions in C. jejuni, and demonstrated the requirement of sigma (28) and sigma (54) for motility. In addition, we show that sigma (28) is involved in the transcription of flaA and that sigma (54) is requi red for transcription of three other flagellar genes, flaB and flgDE. We al so identified two previously uncharacterized genes required for motility en coding proteins that we call CetA and CetB, which mediate energy taxis resp onses. Through our analysis of the Cet proteins, we propose a unique mechan ism for sensing energy levels and mediating energy taxis in C, jejuni.