Persistence and Dissemination of Introduced Bacteria in Freshwater Microcosms

Abstract Genetically engineered microorganisms (GEMs) released into the environment may persist and spread, depending on their features and conditions encountered. In streams, the extent of dispersion depends largely on cycles of attachment to, and detachment from, biofilms, because distribution of microorganisms is limited only by stream flow and settling rates, and because biofilms are the primary generator of bacterial cells. To simulate dissemination of introduced bacteria, multiple antibiotic-resistant bacteria (Chryseobacterium (Flavobacterium) indologenes) were introduced into microcosms containing water, sediments, and leaves. Marked bacteria reached greatest abundances in sediments, and contributions of bacteria from sediments to other habitats was relatively low. Bacterial attachment and detachment occurred rapidly, but the ability of marked bacteria to successfully exploit receiving habitats was comparatively low. Current speed influenced bacterial dissemination. A mechanistic model, using mortality and attachment/detachment rates, determined experimentally, was developed to predict bacterial exchanges in nature. The model was predictive of experimental results when only 5% of bacteria in sediments were available for detachment. Based on model results, an introduced bacterial strain, with mortality rates comparable to those of the model strain, is predicted to maintain highest abundances in sediments. However, within a month, abundance was predicted to be reduced by 98%; long-term persistence is possible if these low population sizes can be sustained. Received: 11 August 1997; Accepted: 9 December 1997