Bacterial Phospholipases

Abstract

Pioneering work by MacFarlane and Knight showed for the first time that a bacterial toxin — the α-toxin of Clostridium perfringens — also had enzymatic activity as a phospholipase C (PLC; MacFarlane and Knight 1941). This finding stimulated great interest not only in the α-toxin but also in the potentially toxic activity of PLC enzymes produced by other bacteria and in the mechanisms that control the production of these proteins. In addition to the PLCs, bacteria have been shown to produce other phospholipases, such as phospholipase Ds (PLDs) and phospholipase As (PLAs), which differ in the site of phospholipid cleavage (Fig. 1). Today, many phospholipases, produced by both pathogenic and non-pathogenic bacteria, have been described and characterised, but only a few of these enzymes have been shown to be lethal toxins. Nevertheless, some of the enzymes considered to be non-toxic have been shown to play important roles in the pathogenesis of disease. Recent studies have suggested that lethality is a rather crude indicator of the potential roles of these enzymes in disease and that many of these phospholipases appear to exert their effects by allowing the bacteria to colonise the host or by perturbing the metabolism of host cells rather than by directly damaging the host (Titball 1993; Songer 1997). These findings have challenged the conventional criteria by which a bacterial product is considered to be a toxin. The aim of this chapter is to review the broad spectrum of bacterial phospholipases, to discuss the mechanisms by which the expression of phospholipaseencoding genes are regulated, to examine the ways in which these enzymes interact with host cells at a molecular level and to illustrate the ways in which bacterial phospholipases contribute to the pathogenesis of disease.