POPULATION-GENETICS OF A TRANSFORMABLE BACTERIUM - THE INFLUENCE OF HORIZONTAL GENETIC EXCHANGE ON THE BIOLOGY OF NEISSERIA-MENINGITIDIS

Information on the biochemistry and genetics of bacterial species, usu ally obtained by the study of single isolates, is enhanced by studies of populations of bacteria. Recent advances in molecular technology, p articularly polymerase chain reaction-based nucleotide sequence analys is, provide powerful tools for the study of population genetics. Data obtained by such techniques indicate that, while some bacterial specie s have a clonal population structure, others are non-clonal or panmict ic. Clonal populations are a consequence of asexual reproduction by bi nary fission; panmictic population structures result from 'horizontal' exchange of genetic material between clones. A consequence of horizon tal genetic exchange is mosaic gene structures, recognisable by compar isons of nucleotide sequences. In transformable bacteria, for example the human pathogen Neisseria meningitidis, several different genes, in cluding the gene encoding the class 1 outer membrane protein, a major surface antigen, are mosaics. This genetic process has implications bo th for vaccine design and in the interpretation of epidemiological dat a.