Bacterial adhesion to different termite flagellates: ultrastructural and functional evidence for distinct molecular attachment modes

The attachment modes of rodlike ectobiotic bacteria to the surface of two d ifferent termite flagellates were studied. Devescovina glabra was covered b y laterally attached bacteria. Treatment with chemicals that disturb hydrop hobic interactions and solubilize proteins removed the ectobionts. Freeze-f racture and freeze-etching electron microscopy revealed rows of intramembra ne particles that occurred exclusively along the attachment sites. The adhe ring Gram-negative bacteria possessed an S-layer (surface layer) composed o f globular protein particles. The S-layer could be removed by protein-solub ilizing chemicals, e.g., urea, as shown by ultrathin-section electron micro scopy Therefore, it seems plausible that the attachment was mediated by hyd rophobic interactions between the flagellate's plasma membrane and the S-la yer of the bacteria. The bacteria of the second flagellate, Joenia annecten s, adhered by their tips. The attachment was extremely strong. Chemicals di sturbing ionic or hydrophobic bindings or solubilizing proteins did not det ach the ectobionts. Globular intramembrane protein particles were preferent ially found in a ringlike array at the external fracture face of the flagel lates contact sites.