Akinori Yoshihara

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

Abstract 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 × 10 6 C/m 3 ) 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.

Measurement of microbial adhesive forces with a parallel plate flow chamber.

HYPOTHESIS It was predicted that the colloidal behaviors of archaea and bacteria with disparate surface structure were different. In this study, the effects of the physicochemical properties of microbial cell surfaces on colloidal behavior were analyzed with Derjaguin-Landau-Verwey-Overbeek (DLVO) theory, thermodynamics, and powder technology. EXPERIMENTS Cell attachment and detachment from model substrates were directly observed using a parallel plate flow chamber. Gram-negative Escherichia coli and archaeal Methanosarcina barkeri were used as model microbial cells, and positively and negatively charged glass slides were used as model substrates. FINDINGS Microbial adhesion on both substrates agreed well with predictions calculated from DLVO theory, using experimental parameters. The total number of cells detached from the substrates as a function of flow rate was fit with the Weibull distribution function. In addition, the drag force required for detachment, which was estimated from the hydrodynamic forces, had a wide distribution; however, the forces became smaller with increasing ionic strength because of reduced electrostatic interactions between the cells and the substrate. M. barkeri could not be detached from positively charged substrates because it would entail a negative change in the interfacial energy of interaction. Thus adhesion was thermodynamically favored in this case.

Estimation of the adhesive force distribution for the flagellar adhesion of Escherichia coli on a glass surface

The effects of the presence or absence of microbial flagella and the microbial motility on the colloidal behaviors of microbial cells were quantitatively evaluated. The microbial cell attachment and detachment processes on a glass surface were observed directly using a parallel-plate flow chamber. Wild-type, flagellar paralyzed, and nonflagellated Escherichia coli strains were used as model microbial cells. In the cell attachment tests, the microbial adhesion rate in a 160mM NaCl solution was approximately 10 times higher than that in a 10mM solution, for all E. coli strains. The colloidal behavior of the microbial cells agreed well with the predictions of the DLVO theory. In addition, the microbial flagella and motility did not significantly affect the cell attachment, regardless of the existence of a potential barrier between the cell and the glass substratum. In the cell detachment tests, the cumulative number of microbial cells detached from the glass substratum with increasing flow rate was fit well with the Weibull distribution function. The list of strains arranged in order of increasing median drag force required to remove them was nonflagellated strain, flagellar paralyzed strain, and wild-type strain. These results indicated that the flagella and the flagellar motility inhibited the cell detachment from the glass substratum. Furthermore, a large external force would likely be required to inhibit the microbial adhesion in the early stage of the biofilm formation.