Lawrence Berkeley National Laboratory

The growth and Cr(VI) reduction by Shewanella oneidensis MR-1 was examined using a mini-bioreactor system that independently monitors and controls pH, dissolved oxygen, and temperature for each of its 24, 10-mL reactors. Independent monitoring and control of each reactor in the cassette allows the exploration of a matrix of environmental conditions known to influence S. oneidensis chromium reduction. S. oneidensis MR-1 grew in minimal medium without amino acid or vitamin supplementation under aerobic conditions but required serine and glycine supplementation under anaerobic conditions. Growth was inhibited by dissolved oxygen concentrations >80 percent. Lactate transformation to acetate was enhanced by low concentration of dissolved oxygen during the logarithmic growth phase. Between 11 and 35oC, the growth rate obeyed the Arrhenius reaction rate-temperature relationship, with a maximum growth rate occurring at 35oC. S. oneidensis MR-1 was able to grow over a wide range of pH (6-9). At neutral pH and temperatures ranging from 30-35oC, S. oneidensis MR-1 reduced 100 mu M Cr(VI) to Cr(III) within 20 minutes in the exponential growth phase, and the growth rate was not affected by the addition of chromate; it reduced chromate even faster at temperatures between 35 and 39oC. At low temperatures (8.5) conditions, 100 mu M Cr(VI) strongly inhibited growth and chromate reduction. The mini-bioreactor system enabled the rapid determination of these parameters reproducibly and easily by performing very few experiments. Besides its use for examining parameters of interest to environmental remediation, the device will also allow one to quickly assess parameters for optimal production of recombinant proteins or secondary metabolites