PROPIONIBACTERIUM SPECIES-DIVERSITY IN ANAEROBIC DIGESTERS

Phenotypic characteristics of 60 strains of Propionibacterium isolated from anaerobic hybrid digesters treating landfill leachate and a bake r's yeast factory effluent were analysed using numerical taxonomy. Wit h the use of the S(SM) similarity coefficient, 92% of the anaerobic di gester strains were grouped in eight major clusters. The isolates were identified by relating them to specific type strains and comparison o f phenotypic characteristics. These clusters were equated with the 'cl assical' species P. acidipropionici, P. freudenreichii, P. jensenii an d P. thoenii using the current classification system. Some of the dige ster isolates were identified to specifies level using the current ide ntification system, but based on overall similarity they were clustere d among members of another species. Furthermore, the data indicated th at there was low similarity between the digester isolates and the type strains of P. jensenii and P. thoeni. A hypothesis is presented as to the role of these propionic acid-producing bacteria during the granul ation process found in anaerobic digesters.