Surface and biofilms On surfaces microbial numbers and activity are usually much greater than in free water because of adsorption effects Bacteria grown on a glass slide immersed in a small river 八 Fluorescence photomicrograph of a natural microbial t community colonizing plant roots in soilSurface and Biofilms On surfaces microbial numbers and activity are usually much greater than in free water because of adsorption effects. Bacteria grown on a glass slide immersed in a small river Fluorescence photomicrograph of a natural microbial community colonizing plant roots in soil