Continuous culture of mixed sediment bacteria in the presence of mercury

Abstract

Continuous culture methods were used to isolate bacteria from sediment from Lake Ontario. These mixed cultures were grown in chemostats at different dilution rates and the glucose concentration in the culture vessel, the optical density, the biomass of cells, and the number and types of bacteria present were monitored for at least 80 generations. Two bacterial types, bothPseudomonas spp., were present at all dilution rates in significant quantities. The mixed cultures exhibited a reciprocal relationship between dilution rate and biomass (and number of bacteria). When Hg was added to the growth medium at a concentration of 5 mg 1⁻¹, the bacteria tolerated that concentration at a dilution rate of 0.117 h⁻¹ substantial changes in the population were noted at a concentration of 10 mg 1⁻¹ Hg. One of the isolates from the mixed culture would not grow at 5 or 10 mg 1⁻¹ of Hg in continuous culture at a dilution rate of 0.066 h⁻¹. In the mixed continuous culture the same isolate showed only minimal response to a Hg concentration of 10 mg 1⁻¹.