FIGURE 1.

Impaired polyamine synthesis in S. pneumoniae impacts the availability of precursors for capsule (CPS) synthesis. Characterization of a putative lysine decarboxylase deletion strain of S. pneumoniae TIGR4 by RNA-Seq and metabolomics identified changes (blue represents increase and red represents decrease) in the genes (italicized) and metabolites in the deletion strain relative to the wild type that could explain the previously reported loss of the capsule. The deletion strain is impaired in the interconversion of UDP-Glu and UDP-Gal via the Leloir pathway (gray square) due to the reduced expression of galk and galT2 genes, that can reduce the availability of UDP-Gal precursor of the repeat unit of the serotype 4 capsule (open white oval). Carbon flux through glycolysis (yellow oval) is reduced in ΔcadA confirmed by the accumulation of glucose 6-phosphate and NAD⁺, intermediates of the pathway and reduced levels of the end product pyruvate. Enzymatic reactions are shown as black arrows and multi-step reactions are represented by a broken arrow. Upregulation of N-acetylglucosamine-6- phosphate deacetylase (NagA^∗) and GlcN6P deaminase (NagB^∗) that could degrade intermediates of UDP-GlcNAc, at the protein level, was earlier reported and was observed at the RNA level in this study. Reduced synthesis of UDP-GlcNAc due to reduced expression of glmS and increased degradation due to higher expression of nagA and nagB will limit the availability of this nucleotide sugar substrate for epimerases that synthesize all three acetylated UDP-sugars of the repeat unit. Accumulation of orotate indicates impaired ability to synthesize UTP, a precursor for UDP-GlcNAc synthesis. The net effect of these changes in metabolism in ΔcadA results in the reduced availability of precursors for CPS synthesis (red rectangle).