Variations in gene organization and DNA uptake signal sequence in the folP region between commensal and pathogenic Neisseria species

Abstract

Background: Horizontal gene transfer is an important source of genetic variation among Neisseria species and has contributed to the spread of resistance to penicillin and sulfonamide drugs in the pathogen Neisseria meningitidis. Sulfonamide resistance in Neisseria meningitidis is mediated by altered chromosomal folP genes. At least some folP alleles conferring resistance have been horizontally acquired from other species, presumably from commensal Neisseriae. In this work, the DNA sequence surrounding folP in commensal Neisseria species was determined and compared to corresponding regions in pathogenic Neisseriae, in order to elucidate the potential for inter-species DNA transfer within this region.

Results: The upstream region of folP displayed differences in gene order between species, including an insertion of a complete Correia element in Neisseria lactamica and an inversion of a larger genomic segment in Neisseria sicca, Neisseria subflava and Neisseria mucosa. The latter species also had DNA uptake signal sequences (DUS) in this region that were one base different from the DUS in pathogenic Neisseriae. Another interesting finding was evidence of a horizontal transfer event from Neisseria lactamica or Neisseria cinerea that introduced a novel folP allele to the meningococcal population.

Conclusion: Genetic recombination events immediately upstream of folP and horizontal transfer have resulted in sequence differences in the folP region between the Neisseria species. This variability could be a consequence of the selective pressure on this region exerted by the use of sulfonamide drugs.

Figure 1

Comparison of gene arrangements in human Neisseriae. The N. subflava sequence (accession number AJ581792 in the EMBL database) is displayed in alignment with corresponding parts from other Neisseria species. Open reading frames are visualized as colored block arrows (the tip of each arrow symbolizing the stop codon) and labeled with their designations according to the text. Non-coding regions are visualized as solid lines. The dedA gene and the Correia element in N. subflava were only partially sequenced. The symbol // means that 13 kb sequence separating tyrB from dedA has been omitted in the figure. The intergenic regions are defined by dotted vertical lines and designated TC (tyrB-cyt5), DM (dedA-manB), MF (manB-folP) and FU (folP-upstream), respectively.

Figure 2

PCR amplification of the region between folP and asmA in Neisseriae. A 1293 base pair product denotes the presence of aroX between folP and asmA. M: molecular marker; a: Neisseria meningitidis (Nm) strain 952 (Su^S); b: Nm 1014 (Su^S); c: Nm BT054 (Su^S); d: Nm 418 (Su^R); e: Nm 3976 (Su^R); f: Nm BT227 (Su^R); g: Nm MO035 (Su^R); h: Nm MO124 (Su^R); i: Neisseria lactamica (Su^S); j: Neisseria cinerea (Su^S). Su^S = sulfonamide-susceptible, Su^R = sulfonamide-resistant.

Figure 3

Enlargement of the intergenic regions from Figure 1. I: region DM. II: region MF. III: region FU. IV: part of region TC. The order of the strains is as in Figure 1: a) Neisseria lactamica; b) Neisseria cinerea; c) N. meningitidis Z2491; d) N. meningitidis MC58; e) N. meningitidis 8013; f) N. gonorrhoeae; g) Neisseria subflava; h) Neisseria sicca. Numbers flanked by dotted arrows specify distances in base pairs between adjacent start- and stop codons. Triangles illustrate various DNA uptake signal sequences: ▷: GCCGTCTGAA; ▶: GTCGTCTGAA; : GCCGTTTGAA; : GCCGTCCGAA; : GCCGTATGAA; : ACCGTCTGAA; : ATCGTCTGAA. Triangles pointing towards each other illustrate inverted repeats. For the complete nucleotide sequences, see Additional file.