Binding of exogenous DNA to marine sediments and the effect of DNA/sediment binding on natural transformation of Pseudomonas stutzeri strain ZoBell in sediment columns

The capacity of marine sediments to facilitate natural transformation of Pseudomonas stutzeri</it> strain ZoBell was investigated. The role of DNA/ sediment binding on transformation frequency was also explored. While transformation frequencies increased as a function of DNA concentrations from 0 to 1.0 µg of DNA from rifampin-resistant strains for filter transformations, transformation in autoclaved sediment columns displayed a reduction in transformation frequency in response to low DNA concentrations (0–1.0 µg/cm3 sediment). Maximum transformation frequencies were obtained on filters at 1.0 µg exogenous DNA, however, maximum frequencies were not reached in sediments until a DNA concentration of 3.0 µg/cm3 sediment was added. When autoclaved sediments were pre-loaded with excess calf thymus DNA, this reduction in response of transformation frequency (cf. filter transformation) was eliminated, i.e., transformation frequencies reached saturation in the preloaded sediments at 1.0 µg DNA/cm3. Autoclaved sediments were shown to bind DNA at a concentration of about 3.6 µg/cm3 sediment, and maximum transformation frequencies were only obtained when these sediments were saturated with DNA. These data indicate that autoclaved marine sediments have the capacity to bind DNA in a form that prevents its availability for natural transformation and only after sediments are saturated with DNA does exogenous DNA become biologically active for natural transformation.