Toxicity of carbon tetrachloride to Dunaliella salina, an environmentally tolerant alga.

Carbon tetrachloride (CCl(4)), a water disinfection by-product, at low environmentally relevant concentrations exerts adverse effects on mammals. The unicellular microalga Dunaliella salina possessing a remarkable degree of environmental adaptation was selected as test organism to investigate low-level exposure to CCl(4). With incubation with less than 0.13% CCl(4), algae responses were similar to control as evidenced by cell growth and levels of beta-carotene, a marker of adaptation. The maximal concentration of CCl(4) that D. salina could tolerate was 0.2%. Algae incubated with more than 0.32% CCl(4) showed decreased growth and reduced beta-carotene levels, which were nondetected after a few days. However, after 98 d, D. salina seemed to revive as evidenced by growth and returned to the biomass similar to control in another 25 d. Randomly amplified polymorphic DNA (RAPD) method was used to compare the genomic DNA difference between control and recovered cells. Polymorphic and repeatable RAPD bands indicated that chronic effects of CCl(4) to D. salina led generation of altered genomic DNA, which may enable the microalga to adapt to survival in an apparently toxic substance environment.