Neisseria genetics

Abstract

The variability of pili and the opacity proteins (Op or P.II) appears to be one of the most significant and intriguing features of the pathogenic Neisseriae. This phenomenon occurs frequently and therefore is different from evolutionary drifts and shifts. Antigenic variation is probably more than a sophisticated mechanism to escape the human immune response; it might be crucial in modulating the virulence properties of the bacterium in different host micro-environments. Much effort has been made by several groups to clarify both the genetic principles, the structural and immunobiological implications of antigenic variation. It became evident that both variable proteins are represented in the genome by multiple variant genes (gene families). Some of these genes are expressed, others are “silent”; intriguing mechanisms seem to be involved in controlling expression. Genetic recombination between individual members of the gene families seems esssential to create new combinations of gene segments that ultimately give rise to variant protein types. One of the frequent mechanisms involved in the recombination of these genes is reminiscent of gene conversion, a mechanism well known from the variation systems of trypanosomes and yeast. Both the pilus and the opacity gene systems of gonococci (now also being evaluated in meningococci) are rather complex and the effort of the bacterial cell to maintain them appears strikingly high. Thus we must envision them as highly significant attributes of these pathogens.