DETECTION AND ENUMERATION OF VIABLE BUT NON-CULTURABLE TRANSCONJUGANTS OF ESCHERICHIA-COLI DURING THE SURVIVAL OF RECIPIENT CELLS IN RIVER WATER

Viable but non-culturable transconjugant cells were detected by a modi fication of the direct viable count (DVC) method, This modification in volved the addition of parental antimicrobial markers (kanamycin and s treptomycin) to the elongation medium in order to promote selective el ongation of the transconjugant cells, Presence of viable, other than c ulturable, transconjugants was demonstrated in matings with parental c ells from TSB culture as well as with recipient cells from survival in river water (under illuminated and non-illuminated systems). In matin gs with a recipient strain from illuminated systems, culturable transc onjugants were not detected after the third day of recipient cell surv ival, In spite of this, viable transconjugants were detected in number s that exceeded 10(5) cells ml(-1). These results clearly show that a fraction of non-culturable recipient cells is able to receive and expr ess plasmids by conjugation processes and form viable but non-culturab le transconjugant cells.