FIG 4.

ΔsrrAB and ΔsarA mutants exhibit reduced growth rates associated with aberrant metabolisms and reduced energy charge following exponential-phase NO˙ exposure. (A) Two phases of growth are observed following the addition of a NO˙ mixture (10 mM NOC-12 and 1 mM DEA-NO) to WT COL during early exponential phase (OD₆₅₀, 0.15): an initial fermentative phase characterized by linear growth rate and lactate production while NO˙ levels are high and a subsequent respiratory phase characterized by resumption of exponential growth and respiration-dependent lactate consumption as NO˙ levels decrease (n = 3). (B) Fermentative and respiratory growth rates of S. aureus COL regulator mutants following addition of the NO˙ mixture at early exponential phase (OD₆₅₀, 0.15) (n = 3). Significance was calculated using Student's two-sided t test (*, significantly different from the WT; P ≤ 0.05). (C and D) Lactate and acetate production (C) and ATP levels (D) were measured periodically following exposure of S. aureus COL strains to the NO˙ mixture. Significance was calculated using Student's two-sided t test (asterisks indicate significant difference from the WT; *, P ≤ 0.05; **, P ≤ 0.01).