PERSISTENCE OF A SURROGATE FOR A GENETICALLY-ENGINEERED CELLULOLYTIC MICROORGANISM AND EFFECTS ON AQUATIC COMMUNITY AND ECOSYSTEM PROPERTIES - MESOCOSM AND STREAM COMPARISONS

Our research objectives were to (i) determine the persistence of an in troduced surrogate (Cellulomonas sp. NRC 2406) for a genetically engin eered microorganism in sediments, growths of Cladophora glomerata (Chl orophyta), and leaf packs, (ii) test community and ecosystem structura l and functional responses to the introduced bacteria, and (iii) evalu ate the utility of flowing water mesocosms as tools for assessing the fates and effects of introduced bacteria in streams. Cellulomonas sp. densities were determined using fluorescent antibodies; maxima were le ss-than-or-equal-to 1% of the total bacterial community in each habita t in two experiments, and almost-equal-to 25% of total densities in le af packs in a third experiment. Densities declined from postinoculatio n maxima faster in sediments than in C. glomerata growths and leaf pac ks. Cellulomonas sp. persisted in leaf packs at densities significantl y greater than background. Cellulomonas sp. had no statistically signi ficant effects on primary productivity, community respiration, assimil ation ratios, photosynthesis/respiration (P/R) ratios, bacterial produ ctivity, and leaf litter decomposition rates. Cellulase concentrations were positively correlated with Cellulomonas sp. densities greater-th an-or-equal-to 7 x 10(8) cells/g dry mass in fresh leaf litter for 2 d ays following exposure. Total bacterial densities, algal biomass, and total viable biomass sometimes differed between control and experiment al systems, but differences were not related to Cellulomonas sp. intro duction. Mesocosms were good tools for studying bacterial population d ynamics in leaf litter and physiological aspects of litter degradation , but they were less well suited to measuring losses of litter mass an d cellulose because physical abrasion during storms accelerated those processes in the field.