Abundance and distribution of anaerobic protozoa and their contribution to methane production in Lake Cadagno (Switzerland)

Abstract

In the uppermost layers of the anoxic sediment in Lake Cadagno, 9 different species of anaerobic protozoa were identified.The total number of these organisms was about 580 cells.zyxwvu ml-' sediment.Most of these protozoa contained endosymbiotic methanogenic bacteria which in total amounted to lo6 methanogens 9 ml-' sediment.In addition to the methanogenic endosymbionts, cells of Metopw setosus and Caenomorpha lata also contained a non-fluorescent bacterial rod inside the cytoplasm.In some individual cells of C. lata this second type of endosymbiotic bacterium was sometimes the only endosymbiont observed.Contrary to earlier suggestions, anaerobic protozoa do not seem to play a major role in methane production at least in Lake Cadagno.No significant methane production due to the anaerobic protozoa and their methanogenic endosymbionts was found in situ.Isolated ciliates and amoebae pro