The physical map of the chromosome of a serogroup A strain of Neisseria meningitidis shows complex rearrangements relative to the chromosomes of the two mapped strains of the closely related species N. gonorrhoeae

Abstract

A physical map of the chromosome of N. meningitidis Z2491 (serogroup A, subgroup IV-1) has been constructed. Z2491 DNA was digested with NheI, SpeI, SgfI, PacI, BglII, or PmeI, resulting in a limited number of fragments that were resolved by contour-clamped homogeneous electric field (CHEF) electrophoresis. The estimated genome size for this strain was 2,226 kb. To construct the map, probes corresponding to single-copy genes or sequences were used on Southern blots of chromosomal DNA digested with the different mapping enzymes and subjected to CHEF electrophoresis. By determining which fragments from different digests hybridized to each specific probe, it was possible to walk back and forth between digests to form a circular macrorestriction map. The intervals between mapped restriction sites range from 10 to 143 kb in size. A total of 117 markers have been placed on the map; 75 represent identified genes, with the remaining markers defined by anonymous cloned fragments of neisserial DNA. Comparison of the arrangement of genetic loci in Z2491 with that in gonococcal strain FA1090, for which a physical map was previously constructed, revealed complex genomic rearrangements between the two strains. Although gene order is generally conserved over much of the chromosome, a region of approximately 500 kb shows translocation and/or inversion of multiple blocks of markers between the two strains. Even within the relatively conserved portions of the maps, several genetic markers are in different positions in Z2491 and FA1090.

Clonal descent and microevolution of Neisseria meningitidis during 30 years of epidemic spread

“…The Opa proteins called 5a, 5f and 5 h were expressed by subgroup III meningococci isolated before the Mecca outbreak, whereas the Opa proteins 5a, 5f and 5i (but not 5h) were expressed by those isolated during or after the Mecca outbreak , suggesting that horizontal genetic exchange have led to the replacement of an opa allele encoding 5h by an allele encoding 5i from an unrelated strain. The opa alleles from subgroup III meningococci have not yet been sequenced but three loci designated opaA, opaB and opaD have been defined in subgroup IV-1 (Hobbs et al, 1994;Dempsey et al, 1995). Furthermore, Opa proteins resembling 5a, 5f and 5h in size and reactivity with monoclonal antibodies (mAbs) had been detected in subgroup IV-1 bacteria isolated in the 1960s and the 1970s and the opa alleles encoding the 5a and 5f proteins have been sequenced from such strains (Hobbs et al, 1994).…”

Two‐dimensional structure of the Opc invasin from Neisseria meningitidis

“…Opa proteins are encoded by a family of opa genes scattered throughout the bacterial genome Bihlmaier et al, 1991), and vary dramatically in sequence, particularly at two cell-surface-exposed hypervariable regions (Connell et al, 1988;Aho et al, 1991). Meningococci have 3-4 opa genes (Aho et al, 1991;Hobbs et al, 1994;Dempsey et al, 1995) while gonococci have 11-12 (Bihlmaier et al, 1991;Bhat et al, 1991;Dempsey et al, 1991). In contrast, only one copy of the opc allele is present per genome for some meningococci (Dempsey et al, 1995), and other meningococci and apparently all gonococci have none (Seiler et al, 1996).…”

Recombinational reassortment among opa genes from ET-37 complex Neisseria meningitidis isolates of diverse geographical origins

“…T o ensure that these sequences corresponded to all four opa loci, the BglII fragments containing opa alleles were excised from pulsed-field agarose gels, and the opa genes amplified by PCR and sequenced directly. Finally, to determine the chromosomal loci of the individual alleles (Dempsey et al, 1995, Morelli et al, 1997, the four opa alleles from both FAM18 and from 24197 were sequenced from PCR products generated using primers from unique regions flanking each opa locus in serogroup A bacteria. PCR products were obtained for all four loci and the sequences were the same as those obtained from excised BglII fragments, showing that the opa alleles in ET-37 complex bacteria are located at the same chromosomal locations as those in serogroup A.…”

“…At least within serogroup A bacteria, these opa genes are located at widely separated chromosomal loci called opaA, opaB, opaD and opal (Dempsey et al, 1995;Morelli et al, 1997).…”