CHEMOSENSORY RESPONSES OF ACANTHAMOEBA-CASTELLANII - VISUAL ANALYSIS OF RANDOM MOVEMENT AND RESPONSES TO CHEMICAL SIGNALS

A visual assay slide chamber was used in conjunction with time-lapse v ideomicroscopy to analyze chemotactic behavior of axenically grown Aca nthamoeba castellanii. Data were collected and analyzed as vector scat ter diagrams and cell tracks. Amebas responded to a variety of bacteri al products or potential bacterial products by moving actively toward the attractant. Responses to the chemotactic peptide formyl-methionyl- leucyl-phenylalanine (fMLP), lipopolysaccharide, and lipid A were stat istically significant (P less than or equal to 0.03), as was the respo nse to fMLP benzylamide (P less than or equal to 0.05). Significant re sponses to cyclic AMP, lipoteichoic acid, and N-acetyl glucosamine wer e also found. Chemotactic peptide antagonists, mannose, mannosylated b ovine serum albumin, and N-acetyl muramic acid all yielded nonsignific ant responses (P > 0.05). There was no single optimal concentration fo r response to any of the attractants tested, and amebas responded equa lly over the range of concentrations tested. Pretreatment of amebas wi th chemotactic peptides, bacterial products, and bacteria reduced the directional response to attractants. Amebas that had been grown in the presence of bacteria appeared more responsive to chemotactic peptides . Treatment of amebas with trypsin reduced the response of cells to ch emotactic peptides, though sensitivity was restored within a couple of hours. This suggests the ameba membrane may have receptors, sensitive to these bacterial substances, which are different from the mannose r eceptors involved in binding bacteria to the membrane during phagocyto sis. The rate of movement was relatively constant (ca. 0.40 mu m/s), i ndicating that the locomotor response to these signals is a taxis, or possibly a klinokinesis, but not an orthokinesis. Studies of the popul ation diffusion rate in the absence of signals indicate that the basic population motility follows the pattern of a Levy walk, rather than t he more familiar Gaussian diffusion. This suggests that the usual math ematical models of ameboid dispersion may need to be modified.