TABLE 3.

Effect of iron deficiency on SOD activity and viable cell number upon depletion of carbon substrate (at t = 0) in the wild type and in a mutant strain of A. vinelandii^a

Strain and iron supplementation (mg/liter) in Burk (no N) medium	SOD activity at t = 0 (U/mg of protein)	% Viable cell no. at:
		0 h	1.5 h	4.5 h
FeSII−
0.015	1.6 ± 0.5	100	61 ± 9	32 ± 6
0.05	1.8 ± 0.3	100	59 ± 7	34 ± 4
0.5	6.9 ± 2.2	100	85 ± 12	70 ± 12
1.0	7.1 ± 1.3	100	76 ± 13	73 ± 9
3.0	7.6 ± 2.0	100	84 ± 10	68 ± 15
Wild type
0.015	1.0 ± 0.4	100	93 ± 4	92 ± 8
0.05	1.1 ± 0.6	100	115 ± 8	96 ± 11
0.5	5.9 ± 0.9	100	96 ± 12	120 ± 15
1.0	6.3 ± 2.0	100	109 ± 13	118 ± 15
3.0	5.9 ± 2.1	100	114 ± 8	132 ± 6

^aThe medium was Burk containing 10 mM sucrose (without iron) and was supplemented with FeCl₃ to the iron level indicated. Dilutions were done in Burk plus N (see text). For SOD activities, cells were harvested and then washed in ice-cold 50 mM HEPES buffer (pH 7.4), and cell extracts were prepared by French pressure cell lysis as described previously (8). Samples (25 μl) containing between 5 to 6.5 mg of protein per ml were added to cuvettes containing 1.5 ml of 0.05 M potassium phosphate (pH 7.8) with all of the other ingredients as indicated previously (7), and 6 μl of xanthine oxidase (Sigma grade IV) was added to start the assay. The viable cell numbers for the two lowest iron supplements are significantly lower than the values for the other iron levels at α′ = 0.01 (Student's t test analysis) for the FeSII⁻ strain. Results are mean ± the standard deviation for five replicate plates (viable cell number data) or three replicate assays (SOD activities).