SURVIVAL OF BACILLUS-LICHENIFORMIS IN SEAWATER MODEL-ECOSYSTEMS

The fate of Bacillus licheniformis DSM 13 was monitored after introduction into laboratory microcosms and mesocosms established in the Knebel Vig estuary, Denmark. The model organism was detected by a combination of immunofluorescence microscopy and nonselective plating followed by colony blotting. This allowed simultaneous quantification of intact cells and culturable cells. B. licheniformis DSM 13 adapted poorly to the conditions in filtered (0.2-mu-m-pore-size filter) seawater. Results from additional microcosm studies using natural seawater demonstrated that protozoan grazing also was important in regulating the population of the introduced model organism. In experiments using mesocosms, B. licheniformis DSM 13 also showed a rapid die-off. The introduction of the organism led to increased nutrient levels and to increased growth of both autotrophic and heterotrophic components of the plankton community compared with those of control enclosures. Thereby, a more intensive predation impact on the bacterioplankton community was induced. The combination of microcosm and mesocosm experiments provides a scenario in which the influence of single biotic and abiotic factors on survival of introduced organisms can be tested and in which the effect of the introduction on ecosystem structure and function can be evaluated. This test concept might prove useful in risk assessment of genetically modified microorganisms.