Growth of mixed cultures ofParacoccus denitrificans andDesulfovibrio desulfuricans in homogeneous and in heterogeneous culture systems.

Obligate aerobes and anaerobes coexist closely in natural ecosystems. One species representative of each class (Desulfovibrio desulfuricans andParacoccus denitrificans) were selected for investigation in different laboratory growth systems. When incubated together, the aerobe protected the anaerobe against oxygen poisoning allowing the latter to grow and to reduce sulfate. When gas phase oxygen tension was systematically altered in stirred batch cultures, both species grew over a broad range of oxygen concentrations. Similar experiments in a chemostat indicated that conditions were far more exacting. No steady state was possible; however, at one critical oxygen tension the two species entered a stable oscillating cycle that lasted for 12 days. When the two organisms were grown in a gradostat in opposing gradients of sulfate plus oxygen and lactate, they coexisted but at different positions in the system. The actual position of the sulfate reducer was determined by the sulfate concentration in the reservoir.