Bisulphite-induced Inactivation of Growth and Chlorophyll Formation inChlorella pyrenoidosa

Treatment of S-sufficient or S-deficient Chlorella pyrenoidosa cells with NaHSO3, during an 8-h period in the light, significantly decreased their chlorophyll and dry matter contents when the cells were incubated in the presence or absence of SO42+. In controls lacking HSO3−, when the starting pH was 7.5, dry matter and chlorophyll contents increased slightly, whereas no significant changes in either occurred at a starting pH of 3.0 when the cells and medium contained SO4−. In the dark, at both pH 3.0 and 7.5, dry matter and chlorophyll contents decreased slightly. Bisulphite treatment in the dark caused little decrease of either dry matter or chlorophyll when cells and medium contained SO42−. However, in its absence, dry matter decreased markedly, but there was little change of chlorophyll content in the dark. The interactions between HSO3− as a source of S and as an inhibitor of growth and chlorophyll formation are discussed in the context of the changes induced by light and alternative sources of S. Overall, the harmful effects of HSO3− outweigh any role it has as a source of S, since its effects are ameliorated by SO42−.