ABSTRACT
Algae-bacteria consortia have been proven effective in the removal of metal pollutants, but the effects of algal-bacterial ratio in the metal accumulation and resistance by this symbiotic system have not been systematically investigated. In this study, we set up consortia with various ratios of Chlorella salina-Bacillus subtilis, determined their growth, Cd accumulation, levels of intracellular glutathione (GSH), extracellular polysaccharide, phosphorus (P) in the culture medium, and functional groups of consortia after Cd treatments (0.1, 0.5, 1 mg L-1 ) for 7 days. With the addition of B. subtilis in the C. salina culture, the dry weight and specific growth rate of the consortia significantly increased compared with C. salina alone, reaching 68.33 mg and 0.382 (mg L-1 ) d-1 respectively at the 1:4 algal-bacterial ratio with 1 mg L-1 Cd treatment. Maximum Cd removal (51.66%) was also observed upon the same Cd exposure and algal-bacterial ratio. Cadmium was mostly taken up into cells at 1 mg L-1 Cd whereas its adsorption dominated the accumulation when Cd was 0.1 and 0.5 mg L-1 . The amounts of extracellular polysaccharides, GSH, and P of the symbiotic system were also increased by the bacterial addition. Besides, Fouriertransform infrared (FTIR) spectroscopy analysis showed that functional groups like N-H, O-H, and P-O-C were involved in the Cd complexation. Taken together, a higher bacterial ratio promoted the Cd accumulation and detoxification by the C. salina-B. subtilis consortia through intra- and extracellular processes.
