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Appl Environ Microbiol. 1986 January; 51(1): 188-196
Copyright © 1986, American Society for Microbiology. All Rights Reserved.

Microbial Ecophysiology of Whey Biomethanation: Characterization of Bacterial Trophic Populations and Prevalent Species in Continuous Culture

² Department of Bacteriology, University of Wisconsin, Madison, Wisconsin 53706, ¹ and Michigan Biotechnology Institute and the Departments of Biochemistry and Microbiology, Michigan State University, East Lansing, Michigan 48824²

ABSTRACT

The organization and species composition of bacterial trophic groups associated with lactose biomethanation were investigated in a whey-processing chemostat by enumeration, isolation, and general characterization studies. The bacteria were spatially organized as free-living forms and as self-immobilized forms appearing in flocs. Three dominant bacterial trophic group populations were present (in most probable number per milliliter) whose species numbers varied with the substrate consumed: hydrolytic, 10¹⁰; acetogenic, 10⁷ to 10¹⁰; and methanogenic, 10⁶ to 10⁹. The three prevalent species utilizing lactose were identified as Leuconostoc mesenteroides, Klebsiella oxytoca, and Clostridium butyricum. Clostridium propionicum and Desulfovibrio vulgaris were the dominant lactate-consuming, hydrogen-producing acetogenic bacteria, while D. vulgaris was the only significant ethanol-degrading species. Methanosarcina barkeri and Methanothrix soehngenii were identified as the dominant acetate-utilizing methanogens, and Methanobacterium formicicum was the prevalent hydrogen-utilizing methanogen. A microbial food chain is proposed for lactose biomethanation that comprises multiple species in three different groups, with the major hydrogen-producing acetogen being a sulfate-reducing species, D. vulgaris, which functioned in the absence of significant levels of environmental sulfate.

^* Corresponding author.

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