Scientists at the Sanger Center, Cambridge, UK, the Max Planck Institute for Molecular Genetics, Berlin, Germany and the University of Oxford have sequenced and analyzed the entire genome of Neisseria meningitidis . These pathogenic bacteria are unusual due to the frequent occurrence of repetitive DNA and extensive genetic variation (Nature, 30 March 2000).
N. meningitidis colonizes the nasopharynx of many healthy individuals but also causes life-threatening meningitis and septicemia in a certain proportion. In industrialized countries, serogroup B and C strains of N. meningitidis are most commonly isolated from endemic disease and localized outbreaks. However, serogroup A strains are associated with large epidemic outbreaks in developing countries, particularly the Sahel region of Africa. In 1997, 500,000 cases of meningococcal meningitis were reported, half of them from Africa. Vaccines based on purified capsular polysaccharides can help stop epidemic serogroup A and C outbreaks but no vaccine is yet available against serogroup B.
Two genomes were described in March, 2000, that of a serogroup B strain (Science 287: 1809-1815) and that of a serogroup A strain (Nature 404: 502-506). Only 91% of the coding sequences of each genome is present in the other strain and other coding sequences are unrelated. Two genomes have also been published for Helicobacter pylori and they also share only 93% of their coding sequences (Nature 397: 176-180, 1999). Comparisons of the sequences of diverse strains showed that both species are characterized by unusually high levels of sequence diversity, even within conserved genes encoding metabolic proteins (PNAS 95: 12619-12624, 1998; Mol Microbiol 32: 459-470, 1999). The present report demonstrates that the genome of N. meningitidis also contains many hundreds of repetitive elements, ranging from short repeats, arranged singly or in multiple arrays, through to insertion sequences and gene duplications of 1 kb or mor
Contact: Mark Achtman