NATURAL TRANSFORMATION IN RIVER EPILITHON

Natural transformation was demonstrated in unenclosed experiments incu bated in river epilithon. Strains of Acinetobacter calcoacsticus were transformed to prototrophy by either free DNA (lysates) or live donor cells. The sources of transforming DNA and recipient culture were immo bilized on filters, secured to stones, and incubated midstream in the river. The transfer frequency generally increased with temperature. No transfer was detected in the river Taff below 10 degrees C. The age o f the recipient culture affected the transformation frequencies in sit u but did not significantly affect the transfer frequency on laborator y media. Transformation of recipient cultures which had been incorpora ted into the natural epilithic biofilm and transformation of the plasm id pQM17 in situ were also demonstrated. This study provides the first direct evidence of natural transformation in situ of bacteria incorpo rated into an indigenous community.