Multi‐stage chemostat investigation of interspecies interactions in a hexanoate‐catabolizing microbial association isolated from anoxic landfill

Spatial separations of physico‐chemical environments (habitat domains) with maintenance of overlapping zones of influence (activity domains) with multi‐stage chemostat models were used to facilitate examination of interspecies interactions within a hexanoate‐catabolizing microbial association isolated from anoxic landfill. Under a constant dilution rate regime, in the presence of 1.4 and 5 mmol/l influent sulphate, consolidation of the major metabolic events of hexanoate catabolism, sulphate reduction, acetogenesis and methanogenesis took place in the first vessel of a five‐vessel array suggesting considerable overlap of activity domains or localization around the habitat domains. Evidence of partial competitive displacement was not apparent until 10 mmol/l of sulphate was used. Introduction of a non‐constant dilution rate regime to a three‐vessel model, subjected to an influent sulphate concentration of 1.4 mmol/l, effected the displacement of the methanogenic species and, as a consequence, in the presence of sulphate limitation, CO 2 reduction became the major sink for excess electrons generated from hexanoate oxidation. A hypothetical scheme of anaerobic hexanoate catabolism by the interacting microbial association was developed.