Mixed chemostat cultures of obligately aerobic and fermentative or methanogenic bacteria grown under oxygen-limiting conditions

Defined mixed cultures of an obligately aerobic Pseudomonas testosteroni and anaerobic Veillonella alcalescens strain were grown under oxygen and lactate limitation in chemostats with different oxygen supply rates. The aerobic and the anaerobic bacteria were shown to coexist and to complete for common substrates over a wide range of oxygen supply rates. Under similar conditions but with formate as the major substrate chemostat enrichments gave rise to undefined mixed cultures of aerobic, fermentative and methanogenic bacteria. The relevance of these observations to natural mineralization processes is discussed