Escherichia coli B was cultured continuously in succinate-minimal medium under conditions of oxygen limitation in the phauxostat. With decreasing oxygenation and consequent decreasing growth rates, the complement of terminal cytochrome oxidases changed as follows: high growth rates, cytochrome o; intermediate growth rates, cytochromes o and d; lowest growth rates, cytochromes o, d, and at. Respiratory kinetics exhibited by nongrowing cell suspensions obtained from continuous cultures indicated that terminal oxidase activity was exhibited by cytochrome o (Km for 02 = 0.2 ,uM; V.,, = 1.1 to 1.5 Amol of 02 per nmol of cytochrome o per min) and cytochrome d (Km for 02 = 0.024 uM; V.,x = 0.7 ,umol
Stable steady-state growth of Escherichia coli B limited by succinate, phosphate, or sulfate ion over the range of specific growth rates of 0.025-0.51 h(-1) was achieved using pH-controlled auxostasis in the phauxostat. The concentration of the growth-limiting substrate in the growth vessel could be varied at will in the region of the Monod half-maximal saturation constants by adjusting the concentration of that substrate in the reservior (at constant buffering capacity) or by varying the population density of the culture through changing the buffering capacity of the medium in the reservoir.
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