Microalgae-associated bacteria play a key role in the flocculation of Chlorella vulgaris

► Flocculation of axenic and xenic cultures of Chlorella vulgaris implicates bacteria. ► DGGE analysis indicates presence of five species of microalgae-associated bacteria. ► FACS treatment of xenic culture implicates three bacterial species in flocculation. ► Bacteria and its extracellular substances increase floc size. ► This study proves that bacteria play a major role in flocculation of microalgae.