Contribution of genes from the capsule gene complex (cps) to lipooligosaccharide biosynthesis and serum resistance in Neisseria meningitidis

Abstract

Within the capsule gene complex (cps) of Neisseria meningitidis B a 5.5 kb DNA fragment encodes proteins with strong homologies to enzymes of the lipopolysaccharide biosynthetic pathway of Salmonella typhimurium and Escherichia coli, GalE, RfbB, RfbC and RfbD. A meningococcal galE mutant expressed a truncated lipooligosaccharide (LOS), which terminated at the glucose residue between inner and outer core, and a second galE gene present outside the cps cluster was found to be transcriptionally and functionally inactive and, thus, unable to complement this defect. Because of the defect in the outer core, the LOS of the galE-defective meningococcal mutant was not sialylated. In contrast, carbohydrate analysis of the LOS of an rfb-defective meningococcal mutant revealed no difference from the LOS of the wild-type strain, suggesting that the rfb genes are inactive. This was supported by Northern blot analysis, which showed that expression of the rfb gene products was transcriptionally regulated. The inability of the meningococcal galE mutant, which cannot sialylate the LOS, allowed us to investigate the significance of LOS sialylation in relation to the presence of the polysialic acid capsule. Sialylated LOS, but not the polysialic acid capsule, is necessary to confer complete serum resistance on the meningococcus by inhibition of the alternative complement pathway.

Expression of sialic acid and polysialic acid in serogroup B Neisseria meningitidis: divergent transcription of biosynthesis and transport operons through a common promoter region

“…Individual deletions of these regions from a cloned copy of the cps complex in E. coli resulted in increases in levels of capsule production, as detected by ELISA (17). Subsequently, Hammerschmidt et al (21) reported that they did not observe a hyperencapsulated phenotype when the region D deletion was reintroduced into the meningococcal host and concluded that the region D genes were not involved in regulation of polysialic acid capsule biosynthesis. Recently, Hammerschmidt et al (22) reported that a transposable genetic element, IS1301, allows serogroup B meningococci to phase-vary capsule production by inserting reversibly into synX.…”

“…The region C and region A genes are divergently transcribed from the intergenic region, and the directions of transcription are indicated by the arrows. Alternative nomenclature for meningococcal biosynthesis genes is as follows: synX (siaA [10], synA [18], neuC [18], and ORF4 [18]), synB (siaB [10], neuA [18], and ORF3 [18]), synC (siaC [10], neuB [18], and ORF2 [18]), and synD (siaB [21], siaD [10], siaG [GenBank-EMBL release 77, accession no. M64289], and ORF1 [18]).…”

Diversity of Microbial Sialic Acid Metabolism

“…In addition to the PSA capsule, meningococci also sialylate their LOS, thereby imparting resistance to host innate immune mechanisms such as antibody-independent complement fixation (57,69,158). Given the diversity of mammalian siglecs and their specificity for distinct sialoglycoconjugates (38), it is likely that sialylated microorganisms interact with host siglec-expressing cells of the myeloid and lymphoid lineages (148).…”

Molecular and Biological Analysis of Eight Genetic Islands That Distinguish Neisseria meningitidis from the Closely Related Pathogen Neisseria gonorrhoeae

“…Some of the clones mapped closely together, suggesting that they may have been derived from larger regions of N. meningitidis-specific DNA. One region containing such clones (region 1) corresponds to the locus of capsule synthesis which had previously been well characterized (8,12,13). However, the significance of the other regions was unknown.…”