GENE-TRANSFER BETWEEN BACTERIA WITHIN DIGESTIVE VACUOLES OF PROTOZOA

The occurrence of horizontal gene transfer between bacteria within dig estive vacuoles and faecal pellets of the protozoan Tetrahymena pyrifo rmis was investigated. More than 90% of the egested faecal pellets of T. pyriformis, added as predator to a suspension of Escherichia coli, contained viable bacteria. In a mixed population, containing donor (pl asmid RP4) and recipient E. coli cells, the presence of T. pyriformis increased conjugational gene transfer by three orders of magnitude. Si nce the protozoa formed an average of 12-13 digestive vacuoles per cel l, each protozoan had statistically egested one or more transconjugant s. Thus, we show for the first time that digestive vacuoles of free-li ving protozoa appear to be an important ecological micro-niche, where gene transfer by conjugation (or retromobilisation) will be favoured. So far, digestive vacuoles have been ignored in genetic and ecological studies. This micro-biotope provides a selective pressure which might enhance the acquisition of virulence genes in cases of mutual interac tions between genetically modified micro-organisms and wild-type patho gens. This finding is important for biosafety considerations.