COFLOCCULATION BETWEEN CA2+-DEPENDENT FLOC-FORMING BACTERIA BELONGING TO THE FAMILY ENTEROBACTERIACEAE ISOLATED FROM SEWAGE ACTIVATED-SLUDGE

Using Ca2+-dependent floc-forming bacteria belonging to the genera Kluyvera, Enterobacter, and Citrobacter and their non-flocculent mutants, bacterial flocculation was investigated in individual and mixed systems. In the absence of Ca2+, all of three flocculent strains flocculated in a different manner in a weakly acidic pH range, but their non-flocculent mutants would not flocculate at all at any pH value. Cells of the flocculent strains were strongly adsorbed by a hydrophobic carrier, Octyl-Sepharose CL-4B, but those of the mutants were scarcely adsorbed. Furthermore, treatment of cells of the flocculent strains with trypsin altered the hydrophobic cell surface to a hydrophilic one. In the presence of Ca2+, three flocculent strains showed good flocculation at pH 7. Coflocculation was also observed between any two flocculent strains. However, trypsin-treated cells of the flocculent strains and cells of the non-flocculent mutants did not coflocculate at all with cells of the flocculent strains.