PROTOZOAN STIMULATION OF ANAEROBIC MICROBIAL ACTIVITY - ENHANCEMENT OF THE RATE OF TERMINAL DECOMPOSITION OF ORGANIC-MATTER

Anaerobic microcosms were established in which plant material was degr aded by the co-operative interaction of various bacterial metabolic ty pes, and the production of CH4 and sulfide was monitored. The introduc tion of the anaerobic ciliate Metopus palaeformis resulted in a reduct ion of bacterial abundance but an increase in the rate of CH4 and sulf ide production. The enhanced bacterial activity (resulting in an incre ased rate of bacterial CH4 production) was positively correlated with the number of ciliates present. The endosymbiotic methanogens of M. pa laeformis did not contribute significantly to the observed increase in CH4 production. It was concluded that protozoan excretions such as or ganic acids (acetate, propionate) were most likely responsible. Protoz oa have previously been shown to enhance bacterial activity in aerobic systems, but this is the first report of the phenomenon in anaerobic systems. Bacterial stimulation by protozoan grazing signifies the impo rtance of anaerobic protozoa in the natural environment, not just in c ontrolling bacterial numbers but also in vitalising ecosystem function . (C) 1998 Federation of European Microbiological Societies. Published by Elsevier Science B.V. All rights reserved.