FIG 2.

Cell recovery via direct count versus plating of the wild-type strain (ES114), AKD915 (Δhmp), and AKD916 (Δhmp Δaox) after growth in mineral salts medium either without (A) or with (B) nitric oxide treatment. Cells were grown in mineral salts medium and, where indicated, treated with DPTA-NONOate. After 6 h, samples were removed for direct counts using a Petroff-Hausser counter (white bars) and plating onto rich medium (gray bars) to determine recoverable CFU. (A) In the absence of nitric oxide, there was no significant difference (P > 0.05) between strains in direct cell counts or CFU recovered after plating. (B) After treatment with nitric oxide, more CFU of a V. fischeri strain lacking hmp and aox (AKD916) than of the parental strain lacking hmp (AKD915) were recovered. Significance for comparisons between direct counts of AKD915 and AKD916 or between plating recovery for AKD915 and AKD916 was measured using Student's t test. *, P < 0.04. No significant difference was detected between direct counts or plating recovery for wild-type cells grown in the presence or absence of NO (P > 0.05) (data not shown). Data shown are averages (±standard error) from one representative experiment containing three independent cultures. Experiments were repeated three times.