Effect of the surface characteristics of Methanosarcina barkeri on immobilization to support materials

To realize a highly efficient anaerobic treatment, it is necessary to immobilize high concentrations of methanogens within a fermenter. In this study, we experimentally examine the effect of the surface characteristics of the acetate-utilizing methanogen Methanosarcina barkeri (JCM 10043) on immobilization to support materials. To this aim, we measured the electrostatic and hydrophobic properties of M. barkeri. The electrophoretic mobility of M. barkeri decreased with increasing ionic strength of the cell suspension and was fitted by the Ohshima equation using two parameters: spatial charge density in the polyelectrolyte region (ZeN = –1.15 × 10⁶ C/m³) and the softness parameter (1/λ = 3.35 × 10⁻⁹ m). M. barkeri showed an affinity to n-hexadecane, with adhesion of more than 60%. M. barkeri showed hydrophobicity relative to Escherichia coli. We also carried out a microbial adhesion test to support materials. M. barkeri showed better adhesion to the anion-exchange resin than to the hydrophobic resin. The microbial cells adhered uniformly to the anion-exchange resin, while coagulated cells adhered non-uniformly to the hydrophobic resin. M. barkeri showed poor adhesion to the cation-exchange resin. The anion-exchange resin is most effective in immobilizing M. barkeri within the fermenter.