VALIDATION OF MICROCOSMS FOR EXAMINING THE SURVIVAL OF PSEUDOMONAS-AUREOFACIENS (LACZY) IN SOIL

Evaluating the safety and efficacy of a recombinant bacterium prior to its release into the terrestrial environment requires that risk asses sment data be collected in the laboratory, Much of this information is obtained with the use of microcosms, The design of the microcosm sign ificantly affects the ability of the recombinant microorganism to surv ive in soil and, thus, complicates the risk assessment process, To sta ndardize microcosms for future use, we evaluated the survival of Pseud omonas aureofaciens 3732 RN-L11 (lacZY Rif(r) Nal(r)) in intact soil c ores (5.0 by 15 cm; polyvinyl chloride core) and disturbed soil microc osms (50 g of fresh, sieved soil), Survival data were compared with th ose obtained during a field release, The intact soil core microcosm wa s shown to closely simulate results obtained in the field, The intact soil core microcosm closely predicts survival in bulk soil and in the rhizosphere of wheat, Data obtained with the microcosm were also simil ar when evaluated in separate studies in two different years, In 1993, P, aureofaciens survived for approximately 63 days in bulk soil and 9 6 days in the rhizosphere, The disturbed soil microcosm exhibited a mu ch more rapid decline in population size (34 days to zero) than the in tact core microcosm, We speculate that drying and sieving of soil for the disturbed soil microcosm affected the ability of the soil to suppo rt the survival of P, aureofaciens, These results demonstrate that a s mall, inexpensive, and simple intact soil core microcosm may be approp riate for risk assessment.