Cadmium tolerance and cadmium removal abilities of four cyanobacteria and two microalgae strains from Benguet [Philippines] mining area

Pure cultures of Chlorella vulgaris Bnt02, Chlorella vulgaris Bnt03, Oscillatoria subbrevis Bnt21, Synechoceptis pevaleckii Bnt07, Synochoceptis pevaleckii Bnt10, Synochoceptis Bnt18 were screened for Cd tolerance by subjecting them to 0.05, 0.50 and 5.00 uM CdCl2 and inoculated into 24-well microtitre plates. Two trials were conducted and three replicates per strain per trial were set-up. The growth responses of each of these strains were evaluated on days 0,7 and 14 by measuring cell densities and determining chlorophylls levels. C. vulgaris Bnt01, C. vulgaria Bnt03, O. subbrevis Bnt21, S. pevaleckii Bnt07 and S. pevaleckii Bnt10 were observed to initially decrease in cell densities as they approached day 7 but however increased as they approached day 14. There was relatively no change in growth of S. pevaleckii Bnt18 from day 7 to day 14. The growth responses of C. vulgaris Bnt01, C. vulgaris Bnt03, O. subbrevis Bnt21, S. pevaleckii Bnt07, and S. pevaleckii Bnt10 were not significantly different from those of the control when the strains were exposed for 7 days and 14 days to 0.05 and 0.50 uM CdCl2. The growth of S. pevaleckii Bnt18 was also not adversely affected when it was exposed for 7 and 14 days to 0.05 uM CdCl2. However S. pevaleckii Bnt18 showed significant difference from that of the control when exposed to 0.05 uM CdCl2 after 7 days and after the end of two weeks. Both cell densities and chlorophyll a levels of C. vulgaris Bnt01, S. pevaleckii Bnt07, S. pevaleckii Bnt10, and S. pevaleckii Bnt18 declined relative to that of the control at 5.00 uM CdCl2. The growth of C. vulgaris Bnt03 differed significantly from that of the control when exposed to 5.00 uM CdCl2 for 7 days. It, however, was not adversely affected as there was no significant difference in growth response form that of the control when the strain was exposed for 14 days to 5.00 uMCdCl2. O. subbrevis Bnt21, on the other hand, was not significantly different in growth response from that of the control when exposed for 7 days to 5.00 uM CdCl2. O. subbrevis Bnt21 was significantly affected relative to that of the control when exposed for 14 days to 5.00 uM CdCl2. Cd tolerance of the 6 strains were lower at greater concentrations, particularly at 5.00 uM CdCl2. The 6 strains showed Cd tolerance since all strains were able to proliferate even after 7 and 14 days of exposure to 0.05, 0.50, and 5.00 uM CdCl2. The 6 strains accumulated Cd mostly in the cytosol. They, however, were able to absorb a small amount Cd on the cell wall. Chlorella vulgaris Bnt03 had the highest capability of Cd removal.