Role of Nematode-Bacterial Interactions in Heterotrophic Systems with Emphasis on Sewage Sludge Decomposition

The role of nematode-bacterial interactions in affecting decomposition was demonstrated utilizing microcosms with sterilized sewage sludge as a substrate. Axenic microcosms were inoculated with the bacterium, Pseudomonas fluorescens (Trevisan), while monoxenic microcosms contained this bacterium and the rhabditid nematode, Pelodera punctata (Cobb). Microcosms were incubated at 5, 15, or 220C. Bacterial density, nematode density, oxygen consumption, and carbon dioxide evolution were determined weekly. Gas flux rates were determined by gas chromatography. For all trials, monoxenic systems had greater (p < 0.01) oxygen consumption than axenic systems. Carbon dioxide flux was less (10 to 75%) due to its high solubility. At 220C, during the period of maximum activity, oxygen consumption was six times greater in those systems containing nematodes, although P. punctata itself accounted for only 5% of the total metabolism. The respiratory metabolism of P. punctata was 7.14 [l 02 h-1 mg-1 dry weight at 220C. Over 35 d, percent organic matter losses in axenic microcosms, were 1.37, 2.47 and 3.51 while in monoxenic microcosms they were 2.52, 6.09, and 6.89 at 5, 15, and 22TC, respectively. Bacterial densities were greater (p < 0.01) in monoxenic microcosms for all trials, with the exception of one trial at 50C. Nematode population doubling times were 24, 5, and 2 d for 5, 15, and 220C, respectively. The time of maximum metabolic activity in the microcosms decreased with the presence of nematodes and/or elevated temp