Abstract
From the view point of fine particle technology, the effects of surface properties of methanogens, which are related to the rate-limiting step in the methane fermentation process, on their adhesion and aggregation were examined. As a result, Methanosarcina barkeri were found to be charged negatively and their isoelectric point was around pH 2. In contrast, Methanosaeta concilii was found to be non-charged and their isoelectric point was around pH 4.5. According to the ATR-FTIR analysis and acid-base titration, it was guessed that the difference of surface potential between two types of methanogens was due to the difference of the amount of carboxyl group and phosphate group on their microbial surface. Methanosarcina barkeri showed better adhesion to not the negatively-charged glass but to the positively-charged one. Percent aggregate of Methanosarcina barkeri increased with an increase in the ionic strength of the cell suspension. In contrast, percent aggregate of Methanosaeta concilii was almost constant regardless of the ionic strength. These adhesion and aggregation phenomena could be understood by the electrostatic interaction and the change of free energy of interaction between methanogen and slide glass.
