FIG. 1.

A steady-state culture of G. sulfurreducens growing at a dilution rate of 0.05 h⁻¹ with fumarate as the terminal electron acceptor was pulsed with 10 mM Fe(III) citrate (arrow). The response of the cell to the pulse was monitored by analyzing the respective respiration products, succinate (filled circles) and Fe(II) (open circles). All the Fe(II) produced was finally washed out of the chemostat as expected in a continuous culture system. Cells were harvested before the Fe(III) pulse, after the Fe(III) pulse (6 h), and when all the Fe(III) was fully reduced to Fe(II) (14 h). RNA was isolated from those cells, and Northern blot hybridization was performed with a specific oligoprobe for frdC (fumarate reductase). The detected transcript corresponds with the 3.3 kb of the frdCAB operon. As a control, parallel cultures were pulsed with the chelating agent citrate, and Northern analysis was performed as described for the Fe(III) citrate pulse.