FACTORS AFFECTING COMPETENCE IN A HIGH-FREQUENCY OF TRANSFORMATION MARINE VIBRIO

Natural plasmid transformation may be a mechanism for the horizontal t ransfer of non-conjugative plasmids in the marine environment, yet the re are few marine model systems available for the study of this proces s. Using multimers of IncQ/P4 plasmids and a filter transformation ass ay, we have measured the effects of nutrients, salinity, temperature, as well as the development and maintenance of competence for genetic t ransformation in the high frequency of transformation (HFT) marine Vib rio strain WJT-1C. Transformation frequency was proportional to the am ount of DNA used from 0.1 to 1.0 mug DNA and was saturated at concentr ations greater than 1.0 mug. Competence began in the early-exponential phase and reached a maximum at the onset of stationary phase. Once at tained, competence was maintained in both spent and nutrient-free medi a for at least 10 d. Thus, the establishment and maintenance of compet ence was unique compared to previously described transformation system s. Temperatures ranging from 4 to 33-degrees-C had no significant effe ct on the maximal transformation frequency of WJT-1C, but at 37-degree s-C the transformation frequency was reduced. However, temperature did affect the rate of the transformation process. Salinities in the rang e 12 to 50 parts per thousand had no significant effect on the transfo rmation frequency but transformation frequencies were lower at 6 parts per thousand and 63 parts per thousand. Cells were transformed equall y well in nutrient-free media or rich media. The ability of this marin e HFT Vibrio strain to develop competence under a wide spectrum of con ditions and to maintain the competent state indicates that natural pla smid transformation could occur in conditions found in tropical and su btropical estuaries.