Sialidase and N-acetylneuraminate catabolism in nutrition of Mycoplasma alligatoris.

The contribution of N-acetylneuraminate scavenging to the nutrition of Mycoplasma alligatoris was examined. The wild-type grew substantially faster (P<0.01) than the mutant strains that were unable either to liberate (extracellular NanI- mutants) or to catabolize (NanA- mutants) N-acetylneuraminate from glycoconjugates in minimal SP-4 medium supplemented only with serum, but the growth of sialidase-negative mutants could not be restored to wild-type rate simply by adding unconjugated sialic acid to the culture medium. In 1 : 1 growth competition assays the wild-type was recovered in >99-fold excess of a sialidase-negative mutant after co-culture on pulmonary fibroblasts in serum-free RPMI 1640 medium, even with supplemental glucose. The advantage of nutrient scavenging via this mechanism in a complex glycan-rich environment may help to balance the expected selective disadvantage conferred by the pathogenic effects of mycoplasmal sialidase in an infected host.