Determinants that govern the recognition and uptake of Escherichia coli O157 : H7 by Acanthamoeba castellanii.

Abstract

Predation by phagocytic predators is a major source of bacterial mortality. The first steps in protozoan predation are recognition and consumption of their bacterial prey. However, the precise mechanisms governing prey recognition and phagocytosis by protists, and the identities of the molecular and cellular factors involved in these processes are, as yet, ill-characterized. Here, we show that that the ability of the phagocytic bacterivorous amoebae, Acanthamoeba castellanii, to recognize and internalize Escherichia coli, a bacterial prey, varies with LPS structure and composition. The presence of an O-antigen carbohydrate is not required for uptake of E. coli by A. castellanii. However, O1-antigen types, not O157 O-antigen types, inhibit recognition and uptake of bacteria by amoeba. This finding implies that O-antigen may function as an antipredator defence molecule. Recognition and uptake of E. coli by A. castellanii is mediated by the interaction of mannose-binding protein located on amoebae's surface with LPS carbohydrate. Phagocytic mammalian cells also use mannose-binding lectins to recognize and/or mediate phagocytosis of E. coli. Nonetheless, A. castellanii's mannose binding protein apparently displays no sequence similarity with any known metazoan mannose binding protein. Hence, the similarity in bacterial recognition mechanisms of amoebae and mammalian phagocytes may be a result of convergent evolution.