The rate-limiting nature of the hydrogen concentration prevailing in the anaerobic digester has been
recognized, but the associated alterations in the microbial community are unknown. In response to the
addition of Enterobacter cloacae cells in laboratory anaerobic digesters, the level of biogas production
was augmented. Terminal restriction fragment length polymorphism (T-RFLP) and real-time polymerase
chain reaction (Real-Time PCR) were used to study the survival of mesophilic hydrogen-producing bacteria
and the effects of their presence on the composition of the other members of the bacterial community.
E. cloacae proved to maintain a stable cell number and to influence the microbial composition of the
system. Bioaugmentation by a single strain added to the natural biogas-producing microbial community
was demonstrated. The community underwent pronounced changes as a result of the relatively slight initial
shift in the microbiological system, responding sensitively to the alterations in local hydrogen
concentration.