Flocculation of a Methylomonas sp.: Possible Involvement of a Surface Protein

Summary: Chemostat-grown cells of a newly isolated strain of Methylomonas were flocculated by the addition of small amounts of positively charged flocculants. The flocculation ability of the cells was almost completely lost after extracting the cells with 1-5 mM-EDTA, or by reducing pH to below 4.5. Reconstitution of the flocculation ability of EDTA-extracted cells was obtained either by the addition of an excess amount of calcium ions, or by mixing dialysed EDTA extracts with EDTA-extracted cells. The EDTA extract contained mainly proteins. The major protein was purified to homogeneity by gel filtration, and had a molecular size of 65000 Dal and an isoelectric point of 9.0. Immunological techniques indicated that this protein was located on the surface of the bacteria. We, therefore, propose that the surface protein of the Methylomonas sp. is involved in flocculation by positively charged flocculants.