Abstract
The electrostatic effects of river sediments(sand) on the transformation of a protease-deficient mutant (NTG-1) of Aeromonas salmonicida were investigated by a laboratory model of river sedi-mets with sonicates of protease positive A. salmonicida, Aeromonas hydrophila, Pseudomonas fluorescence, and Vibrio anguillarum which were used as donor strains. The mutant NTG-1 was induced from A. salmonicida strain A-7301 by mutagenesis, and used as a recipient strain. Trans-formants were determined by protease production as a phenotypic marker for the transformation. The mutant with the sonicate of the parent strain was incubated at 20°C for 20 days with a tracehumic acid and tryptone in the presence or absence of river sand. When a sonicate of the parent strain was added to such cultures, protease positive colonies were isolated in increasing occurrence rate as incubation time was prolonged exclusively in the presence of humic acid, tryptone and sand. Similar results were obtained by using sonicates of the other strains. DNA fragmentsfrom the parent strain were adsorbed by anion exchange resin but not by cation exchange resin. The cells of this mutant were negatively charged, determined by electrophoresis. The trans-formation in the presence of sand is interpreted as showing that DNA fragments (negatively charged) are highly adsorbed on the surface of sand particles (carrying net positive charges), therefore per-mitting bacteria attached to the surface of the particles a high probability of transformation with adsorbed bacterial DNA fragments comprising protease genes.
