Abstract
The genus Neisseria comprises a diverse group of commensal bacteria, which typically colonize the mucosal surfaces of humans and other animals. Neisseria meningitidis, the meningococcus, is notable for its potential to cause invasive meningococcal disease (IMD) in humans; however, IMD is comparatively rare, and meningococci normally colonize the nasopharynx asymptomatically. Possession of a polysaccharide capsule has been shown to be a prerequisite for disease in almost all IMD cases, and was previously considered unique to N. meningitidis, and potentially acquired by horizontal genetic transfer (HGT). Nevertheless, the capsule must also have some role in asymptomatic colonization and/or transmission, consistent with the existence of six non-disease-associated meningococcal capsule serogroups. In this study, full complements of putative capsule genes were identified in non-pathogenic Neisseria species, including Neisseria subflava and Neisseria elongata. These species contained genes for capsule transport and translocation homologous to those of N. meningitidis, as well as novel putative capsule synthesis genes. Phylogenetic analyses were consistent with the proposal that these genes were acquired by the meningococcus through HGT. In contrast with previous evolutionary models, however, the most parsimonious explanation of these data was that capsule transport genes had been lost in the common ancestor of the meningococcus, gonococcus, and their close relatives, and then reacquired by some meningococci. The most likely donor of the meningococcal transport genes was another Neisseria species.
Highlights
The genus Neisseria is a diverse group of Gram-negative bacteria, many of which are asymptomatic colonizers of the mucosal surfaces of animals and man [1]
Capsule gene homologues were identified in isolates from a total of 13 Neisseria species contained within the pubmlst. org/neisseria database [23], including N. bacilliformis (4 of 4isolates); N. elongata subsp. (2 of 4 isolates); Neisseria musculi (1 isolate); Neisseria dentiae (1 isolate); Neisseria animaloris (1 isolate); Neisseria zoodegmatis (1 isolate); Neisseria weaveri (1 isolate); Neisseria canis (1 isolate); Neisseria wadsworthii (1 isolate); Neisseria animalis (1 isolate); N. oralis (4 of 4isolates); N. mucosa (1 of 9 isolates); and N. subflava (17 of 19 isolates)
Annotation using Artemis [25] showed that ctrABCD genes of region C were contiguous and in the same order as those found in N. meningitidis
Summary
The genus Neisseria is a diverse group of Gram-negative bacteria, many of which are asymptomatic colonizers of the mucosal surfaces of animals and man [1]. In humans, they have been isolated from the mouth, nose, throat and urogenital tract, but whilst many Neisseria species belong to the human oral microbiota, research has focused on those associated with disease: Neisseria gonorrhoeae and Neisseria meningitidis. In common with many other Neisseria species, N. meningitidis usually colonizes the nasopharynx asymptomatically; it occasionally invades the bloodstream, leading to life-threatening invasive meningococcal disease (IMD), comprising meningitis and/or septicaemia [2]. Capsules can aid evasion of immune responses, including the complement system and phagocytosis by macrophages, facilitating
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