TY - JOUR TI - Extracellular polysaccharides production by bacteria as a mechanism of mercury tolerance DO - https://doi.org/doi:10.7282/T34X568M PY - 2014 AB - Bacteria have adapted mechanisms of mercury (Hg) tolerance to survive in environments containing elevated Hg concentrations. The potential of extracellular polysaccharides (EPS) production by bacteria as a mechanism of Hg tolerance has not been previously investigated. The objective of my dissertation was to determine if EPS produced by bacteria sorb Hg as a tolerance mechanism. Purified EPS with different chemical compositions isolated from bacterial pure cultures from microbial mats in French Polynesian atolls were assessed for Hg sorption by filtering Hg and EPS solutions after equilibration via shaking and measuring free vs. bound Hg. The data showed that EPS sorbed up to 82% of Hg from solution, that this sorption was dependent on EPS composition, and the sorption was a saturable mechanism. Hg uptake capacities ranged from 1.0 to 91.2 mg Hg/g for the different EPS. To determine if EPS production could alter Hg tolerance in bacteria during growth, an E. coli K-12 strain and its EPS defective mutant were obtained. A disc inhibition assay was performed demonstrating Hg inhibited growth in a dose-dependent manner. The wild-type was more tolerant to Hg with zones of inhibition ranging from 1.4 to 6.1 mm compared to 2.5 to 7.15 mm for the mutant. Assessment of EPS production between the 2 strains by the phenol- sulfuric acid assay for sugar determination normalized to protein content of bacterial pellet showed the wild-type produced 2 times more EPS than the mutant. Finally, EPS production and Hg tolerance were examined in bacteria isolated from an environment with naturally elevated Hg concentrations. Eight obligate and facultative chemolithoautrophic bacteria tolerant to 10 µM HgCl2 were isolated from the East Pacific Rise at 9ºN. Two of the isolates were selected for further characterization. Purge and trap experiments revealed that neither isolate reduced Hg2+ to Hg0 suggesting that the mer operon is not used for mercury tolerance. The phenol-sulfuric acid assay for sugar determination normalized to protein content of bacterial pellets of 3 facultative chemolithoautotrophs revealed that all 3 isolates produced EPS ranging from 0.5 to 38 µg EPS/mg protein. For 2 of strains, there was 8% and 32% increase in EPS production during growth in the presence of Hg, suggesting that EPS may be involved in tolerance. Together these data suggest EPS production is a potential mechanism of mercury tolerance in bacteria. KW - Toxicology KW - Mercury--Absorption and Adsorption KW - Mercury--Toxicology KW - Microbial polysaccharides LA - eng ER -