The Pseudomonas putida strain SP1 was isolated from marine environment and was found to be resistant to 280 mu M HgCl2. SP1 was also highly resistant to other metals, including CdCl2, CoCl2, CrCl3, CuCl2, PbCl2, and ZnSO4, and the antibiotics ampicillin (Ap), kanamycin (Kn), chloramphenicol (Cm), and tetracycline (Tc). mer operon, possessed by most mercury-resistant bacteria, and other diverse types of resistant determinants were all located on the bacterial chromosome. Cold vapor atomic absorption spectrometry and a volatilization test indicated that the isolated P. putida SP1 was able to volatilize almost 100% of the total mercury it was exposed to and could potentially be used for bioremediation in marine environments. The optimal pH for the growth of P. putida SP1 in the presence of HgCl2 and the removal of HgCl2 by P. putida SP1 was between 8.0 and 9.0, whereas the optimal pH for the expression of merA, the mercuric reductase enzyme in mer operon that reduces reactive Hg2+ to volatile and relatively inert monoatomic Hg-0 vapor, was around 5.0. LD50 of P. putida SP1 to flounder and turbot was 1.5x 10(9) CFU. Biofilm developed by P. putida SP1 was 1- to 3-fold lower than biofilm developed by an aquatic pathogen Pseudomonas fluorescens TSS. The results of this study indicate that P. putida SP1 is a low virulence strain that can potentially be applied in the bioremediation of HgCl2 contamination over a broad range of pH.