Rhamnose biosynthesis in mycoplasmas requires precursor glycans larger than monosaccharide

Abstract

Summary Despite the apparent absence of genes coding for the known pathways for biosynthesis, the monosaccharide rhamnose was detected in the D configuration in Mycoplasma pneumoniae and Mycoplasma pulmonis, and in both the D and L configurations in Mycoplasma arthritidis. Surprisingly, the monosaccharide glucose was not a precursor for rhamnose biosynthesis and was not incorporated at detectable levels in glucose-containing polysaccharides or glycoconjugates. In contrast, carbon atoms from starch, a polymer of glucose, were incorporated into rhamnose in each of the three species examined. When grown in a serum-free medium supplemented with starch, M. arthritidis synthesized higher levels of rhamnose, with a shift in the relative amounts of the D and L configurations. Our findings suggest the presence of a novel pathway for rhamnose synthesis that is widespread in the genus Mycoplasma.

O‐linked protein glycosylation in mycoplasma

“…The 13 C‐labelling shown in Figs , http://onlinelibrary.wiley.com/doi/10.1111/mmi.12415/suppinfo confirm that the mycoplasmas have the enzymatic machinery to break down starch and attach glucose to their proteins. As 13 C starch labels the glucose but not the mannose residues of mycoplasma glycoconjugates (Jordan et al ., ), glucose is definitely O ‐linked to six of the glycopeptides identified in Table . The glycans may be variable.…”

“…their proteins. As 13 C starch labels the glucose but not the mannose residues of mycoplasma glycoconjugates (Jordan et al, 2013), glucose is definitely O-linked to six of the glycopeptides identified in Table 1. The glycans may be variable.…”

“…In addition to glycoproteins, M. arthritidis is known to produce a glucolipid (Li et al ., ). This species also synthesizes rhamnose and incorporates it into a glycoconjugate of unknown structure (Jordan et al ., ). Similarly, M. pulmonis produces glycolipid, a glycoconjugate containing rhamnose, the EPS‐I polysaccharide, and possibly multiple glycoproteins as suggested by Fig.…”

“…Also used in this study were M. hominis strain PG21 (ATCC 23114) and M. pulmonis strain CTG (Daubenspeck et al ., ). TnCtrl, M. hominis and M. pulmonis were grown in serum‐free medium as described (Jordan et al ., ) unless indicated otherwise. Mutants in the MARTH_orf819 operon were grown in mycoplasma broth (MB), prepared as described elsewhere (Dybvig et al ., ).…”

“…We have shown that [U-13 C]starch isotopically labels glucose, but not mannose, residues of glycoconjugates of M. arthritidis (Jordan et al, 2013). The mycoplasma was grown in the presence of a 1:1 mixture of 13 C-labelled and unlabelled ( 12 C) starch.…”