INFLUENCE OF CELL WALL COMPOSITION ON THE RESISTANCE OF TWO CHLORELLA SPECIES (CHLOROPHYTA) TO DETERGENTS1

Abstract

ABSTRACTThe influence of dodecylbenzene sulfonate (DBS) and Triton X‐100 (TX‐100) was examined on two species of Chlorella exhibiting conspicuous differences in cell wall composition. Chlorella emersonii has both a classical polysaccharidic wall and a thin trilaminar outer wall (TLS) composed of nonhydrolyzable macromolecules. Chlorella vulgaris lacks a TLS. Photosynthetic capacity was measured following short exposures (1 h) of the algae at different physiological stages to high DBS and TX‐100 concentrations, up to 1 g·L−1. Comparisons with untreated controls indicated that 1) the presence of a TLS in C. emersonii was associated with a very high resistance to the anionic (DBS) and nonionic (TX‐100) detergents at all growth stages, and net photosynthesis was not significantly affected in that species, 2) a high toxicity, particularly pronounced with TX‐100, was observed for actively growing cells of the TLS‐devoid species, C. vulgaris, and 3) aging exerted a protective influence, especially efficient against DBS, on the latter species. Additional observations, including fluorescence spectra and high‐performance liquid chromatography pigment analyses, were conducted following short exposures of actively growing cells. Fluorescence emission spectra revealed that the chlorophyll a‐protein complexes in thylakoid membranes were not substantially affected by DBS and TX‐100, even in the case of C. vulgaris. In sharp contrast, fluorescence excitation spectra on the latter species showed 1) that excitation transfer from antenna pigments to chlorophyll a in reaction centers was substantially altered with both detergents and 2) that the two detergents affected different parts of the photosynthetic system of the TLS‐devoid species. Analyses of C. vulgaris extracts indicated significant decreases in pigment content following exposure to DBS and, to a lesser extent, to TX‐100. Longer exposure experiments (1 day) were conducted with actively growing algae. The TLS‐containing species still showed a very high resistance and no important changes in photosynthetic capacity compared to cells exposed for 1 h. For the sensitive TLS‐devoid species, the detrimental influence of TX‐100, already very high after 1 h, was not increased. DBS toxicity was markedly increased and may reflect a lower uptake rate of DBS by C. vulgaris.Taken together, these observations confirm the important protective role of TLS against detergents. They also provide information on the factors controlling detergent toxicity in the sensitive, TLS‐devoid species and on the different modes of action of DBS and TX‐100 on its photosynthetic system. Such large differences in microalgal sensitivity to detergents, related to TLS occurrence, should have important consequences for the selection of suitable species in toxicity tests.