TABLE 2.

Effect of anaerobic incubation of cells at the time of carbon depletion (t = 0) in the wild type and in an FeSII⁻ mutant strain^a

Strain (gas condition)	Mean (% of initial) viable cell no. (± SD) at:
	1.5 h	3 h	4.5 h
WT (20% O2)	101 ± 17	131 ± 10	136 ± 8
FeSII− (20% O2)	78 ± 12	69 ± 11	74 ± 5
WT (argon)	86 ± 7	85 ± 5	83 ± 8
FeSII− (argon)	92 ± 4	103 ± 12	97 ± 7

^aSidearm flasks with media as described in Table 1 footnote were removed when cells reached an OD₅₈₅ of 0.60 (t = 0), and one set of flasks was tightly stoppered and flushed with argon for 5 min by use of inflow and outflow needles through the stopper. The four flasks were returned to the shaker, and samples taken for determination of viable cell number at 1.5, 3, and 4.5 h after t = 0. Dilutions were done to minimize O₂ exposure (use of argon-flushed dilution media and Ar-sparged stoppered tubes), and 5 mM sucrose was included in the Burk (plus N) dilution medium. According to the Student's t distribution test, data for the argon-incubated samples of both strains were significantly less than for the O₂-incubated samples of the wild type at α′ = 0.01 (99% confidence level) for the 3- and 4.5-h samples. In comparing the wild type (WT) and the mutant in 20% O₂, the mutant results are statistically significantly less than those for the wild type at α′ = 0.01 for the 3- and 4.5-h time points.