A Novel Express Bioassay for Detecting Toxic Substances in Water by Recording Rhodopsin-Mediated Photoelectric Responses in Chlamydomonas Cell Suspensions¶

Abstract

The influence of Cu2+, Zn2+, Cd2+, Pb2+ and formaldehyde on rhodopsin-mediated photoelectric responses in the green flagellate Chlamydomonas reinhardtii was investigated using three modifications of a recently developed population method for electrical recording (in nonoriented, phototactically preoriented (PO) and gravitactically preoriented cell suspensions). The addition of the heavy metal ions at concentrations several times lower than those known to affect swimming velocity and other physiological parameters in photosynthetic 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 their photoelectric cascade, photo-orientation and motility. The signals recorded in PO suspensions were more sensitive to all tested toxic substances than those recorded from nonoriented cells and indicated a switch from negative to positive phototaxis in the presence of the toxic substances. Of the two 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 measurement of the photoinduced electrical responses in Chlamydomonas cell suspensions is a powerful novel bioassay for testing environmental pollutants in water samples.

Amperometric Biosensing Systems Based on Motility and Gravitaxis of Flagellate Algae for Aquatic Risk Assessment

“…Motility-Based Sensing of Toxicity. C. reinhardtii has two flagella at the front edge of the cell and swims by beating them like the breast stroke. − The collective flagellar beatings give rise to bioconvection, which agitates the solution in the vicinity of the electrode, as well as in the solution bulk. As the stirring effect increases, the thickness of the diffusion layer decreases on the electrode surface.…”

“…Changes in the collective flagellar movement of flagellate alga, Chlamydomonas reinhardtii, were monitored as changes in the redox currents for a coexisiting redox marker. Furthermore, the alga exhibits negative gravitaxis, which is one of the algal physiological activities to swim against gravity, in conjunction with swimming motility. − These activities are known to be inhibited by exposure to some organic compounds and heavy metal ions. A system that monitors the gravitaxis as well as motility was also developed.…”

Electrochemical System for the Simultaneous Monitoring of Algal Motility and Phototaxis

“…The light intensity was ∼100 μW cm -2 at working electrode 1 (W.E.1). The electrochemical cell was irradiated with a red light, which has no effect on phototaxis but maintains cell motility, , using a fluorescent lamp (ETA15ELR13-SHG, NEC) and a filter (no. 20, Tokyo Butai Shomei, λ > 600 nm) before (for more than 10 min) and during the measurements.…”