Adsorption of mercury and copper ions by oral microorganisms

The metal ion accumulation by oral bacterial cells was investigated in this study using two heavy metals, copper and mercury at pH 4.0 and 7.0. However, the adsorption rate of mercury was especially examined at pH 4.0 because of the loss of metal ions caused by the adsorption on the walls of the container and the occurrence of volatilization at pH value on the neutral and alkaline side.Higher mercury adsorption by bacterial cells were demonstrated in Propionibacterium acnes, Treponema denticola and Eikenella corrodens in order of strength at pH 4.0. Regarding copper ion adsorption by oral bacteria, the higher metal adsorptions were also shown at pH 4.0 and 7.0 in P. acnes, Peptostreptococcus anaerobius and Corynebacterium matruchotii, respectively.The metal adsorptive abilities of these oral microorganisms appeared to be higher than that of Actinomyces levoris which had extremely high uranium accumulation abilities etc.There were no marked differences between the intact cells and the lyophilized cells of P. acnes, even when treated with heat at 100°C for 10 min.These metal ion adsorptions by microorganisms always proceeded immediately after adding metal to bacterial suspension and reached a plateau around 5 min later.These findings obtained strongly suggest that some oral bacteria have the potential the adsorption of heavy metal ions, and that the mode of adsorption is based on a physico-chemical action governed by the Freundlich adsorption isotherm equation.