A novel express bioassay for detecting toxic substances in water by recording rhodopsin-mediated photoelectric responses in Chlamydomonas cell suspensions

The influence of Cu2+, Zn2+. Cd2+. Ph2+ and formaldehyde on rhodopsin-media ted photoelectric responses in the green flagellate Chlamydomonas reinhardt ii was investigated using three modifications of a recently developed popul ation method fur electrical recording (in nonoriented, phototactically preo riented (PO) and gravitactically preoriented cell suspensions). The additio n of the heavy metal ions at concentrations several times lower than those known to affect swimming velocity and other physiological parameters in pho tosynthetic flagellates led to a rapid (one to several minutes) inhibition of the responses. Formaldehyde induced a significant temporary increase in the gravi-orientation of the cells simultaneously with an inhibition of the ir photoelectric cascade, photo-orientation and motility. The signals recor ded in PO suspensions were more sensitive to all tested toxic substances th an those recorded from nonoriented cells and indicated a switch from negati ve to positive phototaxis in the presence of the toxic substances. Of the t wo major components of the photoelectric cascade, the regenerative response was more sensitive to the tested heavy metal ions, but not to formaldehyde , than the photoreceptor current. The results obtained show that measuremen t of the photoinduced electrical responses in Chlamydomonas cell suspension s is a powerful novel bioassay for testing environmental pollutants in wate r samples.