Cell to cell recognition between the ciliatePseudomicrothorax dubius and its food organisms: the role of surface charges

Summary The importance of charged groups during phagocytic recognition of filamentous Cyanobacteria (Oscillatoria formosa andAnabaena spp.) by the stenophagic ciliatePseudomicrothorax dubius has been studied. Anionic and cationic domains are evenly and randomly distributed over the cyanobacterial surface, as demonstrated with scanning electron microscopy following labeling with colloidal gold (–) and colloidal gold coupled with poly-L-lysine (+). The phagocytosis ofOscillatoria was inhibited when filaments were treated with cationic reagents such as poly-L-lysine (pLL), FeCl₃ and carbodiimide. In contrast elimination of cationic charges on theOscillatoria surface by treatment with poly-L-glutamic acid (pLGa) or colloidal gold did not affect phagocytosis. The effects of sequential treatment with pLL and pLGa demonstrated that pLL reduced phagocytosis of pLGa-pretreatedOscillatoria, whereas the pLGa restored phagocytosis of pLL-pretreated filaments. Scanning electron microscopy showed that pLL- or pLGa- treated filaments can still adsorb the oppositely charged colloidal gold particles on their surface. However, the treatment of filaments with pLL followed by pLGa prevented subsequent labeling with gold as well as with pLL-gold particles. Filaments ofAnabaena spp., which are not normally ingested byPseudomicrothorax, were also treated individually or sequentially with pLL and pLGa. None of these treatments, however, provoked phagocytosis ofAnabaena byPseudomicrothorax. We suggest that the surface charge alone does not play a crucial role in phagocytic recognition inPseudomicrothorax and that phagocytosis-specific molecules are implicated.