The integration site of the iga gene in commensal Neisseria sp

An IgA1 protease is produced by the human pathogens Neisseria gonorrhoeae and N. meningitidis but not by related non-pathogenic, commensal, Neisseria species. In this study, the chromosomal iga locus was characterized in the N. gonorrhoeae strain MS11 and compared to corresponding loci in N. meningitidis and commensal Neisseria species. In N. gonorrhoeae, the genes trpB and ksgA were found immediately downstream of iga. In addition to comL and comA, a homolog of the Escherichia coli YFII gene was identified upstream of iga. Each gene in the iga region (YFII and comL, comA and iga, and trpB and ksgA) is transcribed in the opposite direction to its neighbors. The comL/ comA and iga/ trpB pairs each have a transcriptional terminator in the correct position for joint use. These terminators contain the common gonococcal DNA uptake sequence (DUS). A highly conserved direct repeat of 25 bp located immediately adjacent to the iga gene in N. gonorrhoeae was also found in N. meningitidis. In Southern hybridization experiments, no homology to iga was detectable in the chromosomal DNAs of the commensal species N. mucosa, N. lactamica, N. flavescens, N. cinerea, N. subflava, N. flava, N. sicca or N. elongata. When N. gonorrhoeae comL and trpB were used as probes, signals were detected on the same restriction fragment in six of the eight species. This indicated that commensal Neisseria species share a possible integration site for the iga gene between comA and trpB. The region between comA and trpB was therefore amplified by PCR. The fragment obtained from N. lactamica showed a high degree of homology to gonococcal comA and trpB, respectively, but iga was replaced by a sequence of 13 bp that shows no homology to any known gonococcal sequence. Our data suggest that iga was acquired by a common ancestor of N. gonorrhoeae and N. meningitidis rather than being distributed by horizontal gene transfer. N. lactamica, which is more closely related to N. gonorrhoeae than other commensals, may have lost iga by deletion.