Arginine biosynthesis in Campylobacter jejuni TGH9011: determination of the argCOBD cluster

Arginine biosynthetic genes from Campylobacter jejuni TGH9011 were cloned b y functional complementation of the respective Escherichia coli arginine bi osynthetic mutants. Complementation of argA, argB, argC, argD, argE, argF, and argH auxotrophs was accomplished using a pBR322-based C. jejuni TGH9011 plasmid library. By cross-complementation analyses, the first four steps o f arginine biosynthesis were shown to be closely linked on the genome. Two additional clones complementing the first (ArgA) and fifth (ArgE) steps in arginine biosynthesis were obtained. Neither recombinant showed linkage to the arg cluster, to each other, nor to other arginine biosynthetic function s by cross-complementation. Genes argF and argH were not linked to other ar ginine biosynthetic genes by cross-complementation analysis. Restriction en zyme patterns of recombinant plasmids fell into five groups. Group I contai ned the arg(ABCD) complementing locus. Group II and Group III were the two genetic loci corresponding to the argA and argE complementing genes. Group II contains the hipO gene encoding N-benzoylglycine-amino-acid amidohydrola se, also known as hippurate hydrolase. Group III contains the hipO homolog of C. jejuni. Group IV represents the argF gene. GroupV is theargH gene. Fu nctional complementation of mutations in the first four steps of the argini ne biosynthetic pathway was obtained on recombinant plasmid pARGC2. The pre dicted order of gene complementation was argCargA(argBargD). The sequence o f the insert in plasmid pARGC2 revealed direct homologs forargC, argB, and argD. However, sequence analysis of the gene complementing ArgA function in two separate E. coli argA mutants determined that the C. jejuni gene was n ot a canonical argA gene. The gene complementing the argA defect, which we call argO, showed limited homology to the streptothricin acetyltransferase gene (sat) of Escherichia coli. The flanking open reading frames in pARGC2 showed no homologies to arginine biosynthetic genes. The structure of the a rgCOBD gene arrangement is discussed with reference to the presence and loc ation of other arginine biosynthetic genes on the genome of C. jejuni and o ther bacterial organisms.