Light and Electron Microscopic Examinations of Methane-Producing Biofilms from Anaerobic Fixed-Bed Reactors

Abstract

Ultrastructural examinations were performed on biofilms from 8 anaerobic fixed-bed reactors filled with various packing materials and operated on fresh swine waste. By using light and UV microscopy and scanning and transmission EM, the distribution of a diverse microbial population composed of bacteria and a few yeasts was determined. This is the 1st time that the ultrastructure of in situ anaerobic digestor biofilms has been reported. Many methanogenic bacteria were identified by their fluorescence under 420 nm radiation. Of these, 2 morphologically distinct types were most prevalent in the films. Methanothrix spp. were present in high numbers at the film surface; Methanosarcina spp. were commonly embedded in the lower regions of the film. Inhabitants of the film were surrounded by an exopolysaccharide matrix that was very dense toward the base. An extensive network of channels, that may facilitate gas and nutrient exchange to the lower regions of the film was observed throughout the matrix.