A MODIFIED SOS-CHROMOTEST PROCEDURE TO TEST FOR GENOTOXICITY AND CYTOTOXICITY IN SEDIMENTS DIRECTLY WITHOUT EXTRACTION

A modified SOS-Chromotest bioassay using a chromogenic pad (pad proced ure) was developed to test for genotoxicity in sediments directly with out extraction. This test is based on the de novo synthesis of beta-ga lactosidase enzyme by a genetically-engineered E. coli strain PQ37. In the bioassay, an exponential growth phase antibiotic-containing cultu re of the test bacterium is introduced into a series of tubes with the first tube containing 0.1 gram of sediment. Serial dilutions are then made and the tubes of sediment plus bacterial culture are incubated a t 37 degrees C for four hours, followed by placing a drop of each mixt ure on a chromogenic pad and additional incubation for 20 hours at 37 degrees C. The solid particulates are then washed off with tap water a nd positive (genotoxic) activity is noted by the presence of a distinc tive blue colour on the pad. The SOS-Chromotest pad procedure may be b est used as a relative measure of genotoxicity by comparing results to a reference sample. In addition it can also determine sediment cytoto xicity by comparing samples spiked with a genotoxic standard (i.e., 4- nitroquinoline-N-oxide). Preliminary results suggest that this new bio assay is highly sensitive, consistent and discriminating.