Sequestration and Distribution Characteristics of Cd(II) byMicrocystis aeruginosaand Its Role in Colony Formation

Abstract

To investigate the sequestration and distribution characteristics of Cd(II) byMicrocystis aeruginosaand its role inMicrocystiscolony formation,M. aeruginosawas exposed to six different Cd(II) concentrations for 10 days. Cd(II) exposure caused hormesis in the growth ofM. aeruginosa. Low concentrations of Cd(II) significantly induced formation of smallMicrocystiscolonies (P<0.05) and increased the intracellular polysaccharide (IPS) and bound extracellular polysaccharide (bEPS) contents ofM. aeruginosasignificantly (P<0.05). There was a linear relationship between the amount of Cd(II) sequestrated by algal cells and the amount added to cultures in the rapid adsorption process that occurred during the first 5 min of exposure. After 10 d,M. aeruginosasequestrated nearly 80% of 0.2 mg L−1added Cd(II), while >93% of Cd(II) was sequestrated in the groups with lower added concentrations of Cd(II). More than 80% of the sequestrated Cd(II) was bioadsorbed by bEPS. The Pearson correlation coefficients of exterior and interior factors related to colony formation ofM. aeruginosarevealed that Cd(II) could stimulate the production of IPS and bEPS via increasing Cd(II) bioaccumulation and bioadsorption. Increased levels of cross-linking between Cd(II) and bEPS stimulated algal cell aggregation, which eventually promoted the formation ofMicrocystiscolonies.