Characterization and theoretical analysis on toxicological threshold of mercuric ions to Pseudomonas aeruginosa PU21 (Rip64)

This study provides a novel attempt to put forward, in general terms and explanations, the toxicological threshold for Hg(II) detoxification. Quantitative analysis of mercuric ion toxicity to a mercury-resistant strain Pseudomonas aeruginosa PU21 and identification of the threshold phenomena are included. It is revealed that rate of cellular viability loss depends upon the ratio of Hg2+ concentration to cell population, (or "multiplicity of toxicity" - MOT). The threshold of unacclimated cells (or "non-growth cells" PU21(u)) and hyperresistant strain (PU21(r)) occurs at MOT of 1.6 x 10(10) N 3.2 x 10(10) and 1.7 x 10(11) N 3.4 x 10(11) molecules Hg2+/Cfu, respectively. The threshold of PU21(u) increase approx. 10-fold compared with unacclimated resistant strain PU21(u). This indicated that sequential treatment of culture with selection pressures (i.e. mercury-containing media) led to over 10-fold increase in mercury resistance. Thus, this quantitative evaluation of toxicity threshold among resistant populations can be used as a design criterion for long-term Hg2+ detoxification bioprocesses.