Dielectric Measurement of Euglena gracilis as a Multi-parametric Approach for Non-invasive Biomonitoring of Aquatic Environment
Abstract
Dielectric spectroscopy was employed for monitoring biophysical parameters of Euglena gracilis in suspension to assess a possi bility of using this method for a new biomonitoring system for detecting and identifying pollutants in aquatic environments. E. gracilis was subjected to different types of membrane -affecting toxic chemicals (1 mM chlorpromazine, 1 mM HgCl 2, or 1 mM Triton X-100), and dielectric measurement of the cell suspension w as carried out over a wide frequency range between 5 kHz and 3 MHz. All of these chemicals at the designated concentrations induced similar changes in cell motility of Euglena cells; flagellar act ivity was inhibited and rounding -up movement of the cell body was induced. These chemicals also induced distinct changes in dielectric properties of the cell suspension, but the manner of changes in dielectric behavior was unique to individual chemical spe cies, suggesting a possible use of this technique for quick identification of toxic materials in aquatic environments.
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Introduction
Identification of toxic substances in various samples, such as drinking water and food specimens, is exceedingly important, but analytical methods by using chemical procedures require time -consuming and labor -intensive sample preparations [1]. Therefore, biomonitoring approaches have been developed to rapidly identify toxicity using living organisms such as microorganisms [2], animals [3, 4], unicellular algae [5], and protists [6] as biomonitors. Although biomonitoring allows evaluation of cumulative effects of various contaminants, it is not possible to identify and name the chemical substances contained in the polluted water. Tahedl and Häder [7, 8] reported an approach for monitoring water quality by using the motile unicellular flagellate Euglena gracilis as a monitoring organism. They developed an elaborate system to determine six different movement parameters including motility, swimming velocity, and gravitactic orientation, and showed that different chemicals affect different parameters [7]. E. gracilis is suitable as a biomoitor organism, since 1) methods f or axenic mass cultivation has been established [9], 2) free -swimming motility ensures a long -lasting homogeneous cell suspension that is required for stable measurement, and 3) the cells have a uniform and symmetrical morphology that changes in response to various environmental factors [10].
Dielectric spectroscopy is a non -invasive technique by which multiple electrical and morphological parameters of the living cells in suspension can be obtained over a wide frequency range [11, 12]. In this paper, we have applied this method to E. gracilis , as an attempt to evaluate the possibility that different multiple parameters obtained by this technique might be useful to quickly unveil the chemical composition of unknown water samples.
Conclusion
Biomonitoring of water quality is essential for the safe supply of drinking water, which offers many advantages over the classical physico -chemical methods of analyses. They usually involve simple observations, and requires only short time, small money and space. However, biomonitoring also ha s disadvantages. They are not able to provide an exact figure of water quality parameters, and cannot pinpoint the exact cause of water quality problems. It is principally because biomonitoring techniques usually employ only a single parameter (swimming behavior, electromyographic response, etc.), although chemical nature of toxicant s is highly complicated. In the present paper, we found different dielectric responses that are characteristic t o three different toxic chemicals, even though they showed similar morphological and behavioral responses to E. gracilis . If we can make good use of a set of multiple dielectric parameters extracted from the wide frequency -range data, it should provide us with a good starting point to identify individual toxicant s contained in polluted water samples .
