Influence of pH on the survival of Dictyosphaerium chlorelloides populations living in aquatic environments highly contaminated with chromium

• Dc1MCr(VI)R25 strain tolerates high concentrations of Cr(VI) in the culture medium.
• pH values below 4.25 decrease the cell viability of Dc1Mwt and Dc1MCr(VI)R25 strains.
• In acidic cultures, cell viability of Dc1MCr(VI)R25 is slightly higher than Dc1Mwt.
• Both strains have similarly affected photosynthetic activity under acidic conditions.

The accommodation of photosynthetic organisms to adverse conditions, such as pH changes in the aquatic environment, and their response to aquatic pollutants is essential to develop future biosensors. The present study reports the ability of both Cr(VI)-sensitive and tolerant Dyctiosphaerium chlorelloides strains to live in aqueous solutions highly contaminated with hexavalent chromium under varying ranges of pH, by the determination of chromium toxic effects on these strains. Studies of cell growth, photosynthetic quantum yield and gross photosynthesis rate show that both D. chlorelloides strains are able to survive in alkaline and moderately acidified (pH 4.25) aquatic environments. Below this pH value cell populations from both strains exposed for short periods of time to Cr(VI) showed alterations in the three parameters studied. There were no significant differences comparing the response of both strains at pH change in the culture medium. However, Cr(VI)-tolerant strain exhibits a better fit to maintain cell growth than Cr(VI)-sensitive strain when both were subjected to pH 4.25 in the culture medium. The absence of significant differences in photosynthetic activity results for both strains suggests that the lower sensitivity exhibited by Cr(VI)-tolerant strain would be due to cellular morphological changes rather than changes in cellular activity.

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