The ultrastructure of the major species of an enriched methanogenic culture utilizing acetic acid

Abstract

The ultrastructure of the cells of the major component of an enriched culture of a presumed methanogen which utilized acetic acid was studied by transmission and scanning electron microscopy. The filaments were composed of Gram-positive, rod-shaped cells, 1--2 micrometer in length and about 0.5 micrometer in breadth, attached end to end. Septa between cells were complex, with a central, electron-dense sheet which had a spherical enlargement in the center separating the cell walls. The cells walls themselves were of variable thickness with a light, fluffy, thin portion on the outside and a denser, thicker portion within. They contain a series of rings stacked side by side which are composed of material that stains strongly and positively with phosphotungstate ion. The cytoplasmic membrane of these cells had an outer leaflet which stains more densely with uranium and lead ions than the inner leaflet. There were no recognizable organelles in the cytoplasm other than ribosomes. It is shown in these observations that the presumed methanogen may likely be a new species.

Effect of Support Material on the Development of Microbial Fixed Films Converting Acetic Acid to Methane*

“…Filament length was shortest on etched glass and longest on clay supports. This filamentous micro-organism has been described previously by Colvin et al (1979) and appears to be the same as the 'fat rod' or 'acetate organism' seen in many acetate enrichments of digester sludge (Mylroie & Hungate 1954;Pretorius 1972;Ferry & Wolfe 1976;van den Berg et al 1976;Zehnder et af. 1980).…”

“…Polished clay, while much smoother to the touch than unpolished clay, undoubtedly retained pores of such diameter. Nevertheless, the roughness of unpolished clay may shelter the micro-organisms from physical disturbances such as currents, thereby reducing the break up of the filaments into single cells (Colvin et al 1979;Zehnder et af. 1980) and the loss of cells from the film.…”

“…The culture used in the attachment study was an enrichment culture composed almost exclusively of bacteria converting acetic acid to methane (van den Berg 1977;Colvin et al 1979;Hoban & van den Berg 1979;van den Berg et al 1980) and very similar in appearance and characteristics to the enriched culture described by Zehnder et al (1980). These bacteria are considered to be major converters of acetic acid in mesophilic anaerobic digesters.…”

“…Scanning electron micrographs were prepared of each of the fixed films attached to etched glass, PVC plastic and clay, after the films had developed for 70 d. The method of preparation of the electron micrographs was essentially that described by Colvin et al (1979), with the exception that the particles of clay with fixed film had to be placed on conducting tape to obtain a good transmission of electrons.…”

Isolation and characterization of an aceticlastic methanogen from a biogas digester

“…The present paper reports the isolation and characterization of a fast growing filament-forming methanogen which utilises acetate as the sole energy source for growth. This organism is similar to the bacterium described by Srhngen in 1906, and later which was observed by many investigators in their acetate enrichments [7,[14][15][16][17][18][19][20] or in enrichment cultures on various substrates with acetate as a free intermediate [21][22][23][24][25], and recently obtained in pure form and named Methanothrix srehngenii [ 1 O, 11 ].…”