Fig. 3.

Contribution of N-acetylneuraminate scavenging to the growth of Mycoplasma alligatoris . The smoothed curves represent the mean number of colony-forming units (c.f.u.) of two independent clones of each mutant phenotype. (a) Knockouts that were unable to liberate (extracellular Nanl⁻) or catabolize (NanA⁻) N-acetylneuraminate grew more slowly than the wild-type in minimal SP-4 medium supplemented only with serum (Dunnett’s P<0.01 by 8 h). (b) All genotypes grew ~twofold more slowly in 0.3 mM N-acetylneuraminate-supplemented SP-4 medium with serum than in unsupplemented medium with serum (P<0.05). Presumptive toxicity was evident by 16 h in the NanA⁻ knockouts. (c) In direct growth competition assays, the fraction of NanI⁻ colonies recovered after co-culture on fibroblast monolayers in glucose-free medium (solid line) inoculated with mutant TNP1C23 mixed 1 : 1, 10⁴ : 1 or 10⁷ : 1 with the wild-type was 0.5, 4.0 and 55.6 %, respectively; inoculation in those ratios yielded only 0.5, 3.5 and 42.6 % NanI⁻ colonies even in glucose-supplemented medium (dashed line).