Identification and characterization of nuclease activities in anaerobic environmental samples

DNA-degrading activity from anaerobic samples of bovine ruminal fluid, primary anaerobic digestor wastewater, freshwater sediments, and marine sediments was observed in the presence of 5 mM EDTA. Nuclease activity experiments involved exposing salmon chromosomal DNA to the environmental samples in 50 mM pH 7.2 buffer, incubating at 37 degrees C, and subjecting the products to electrophoresis. The same stock and concentration of EDTA used in these assays (5 mM) completely inhibited commercial grade DNase. Nuclease activity in two of the samples, ruminal fluid and wastewater, was further characterized. DNA degradation in the ruminal sample was significantly reduced when EDTA or citrate concentrations were increased to 50 mM or above. DNA degradation activity in ruminal fluid was associated with material that passed through a 0.22-micron filter, but wastewater activity was associated with material retained by a 3-micron filter. Degradation activity in the wastewater was resistant to heat pretreatment, whereas the rumen activity was heat-labile (70 degrees C, 60 min). These results demonstrated the biochemical complexity of these two environments and that high molecular weight DNA has a short half-life in these anaerobic environments.