PERSISTENCE AND DISSEMINATION OF INTRODUCED BACTERIA IN FRESH-WATER MICROCOSMS

Genetically engineered microorganisms (GEMs) released into the environ ment may persist and spread, depending on their features and condition s encountered. In streams, the extent of dispersion depends largely on cycles of attachment to, and detachment from, biofilms, because distr ibution of microorganisms is limited only by stream flow and settling rates, and because biofilms are the primary generator of bacterial cel ls. To simulate dissemination of introduced bacteria, multiple antibio tic-resistant bacteria (Chryseobacterium (Flavobacterium) indologenes) were introduced into microcosms containing water, sediments, and leav es. Marked bacteria reached greatest abundances in sediments, and cont ributions of bacteria from sediments to other habitats was relatively low. Bacterial attachment and detachment occurred rapidly, but the abi lity of marked bacteria to successfully exploit receiving habitats was comparatively low. Current speed influenced bacterial dis semination. A mechanistic model, using mortality and attachment/detachment rates, determined experimentally, was developed to predict bacterial exchang es in nature. The model was predictive of experimental results when on ly 5% of bacteria in sediments were available for detachment. Based on model results, an introduced bacterial strain, with mortality rates c omparable to those of the model strain, is predicted to maintain highe st abundances in sediments. However, within a month, abundance was pre dicted to be reduced by 98%; long-term persistence is possible if thes e low population sizes can be sustained.