Comparing Galactan Biosynthesis in and .

The suborder Corynebacterineae encompasses species like , which has been harnessed for industrial production of amino acids, as well as and , which cause devastating human diseases. A distinctive component of the Corynebacterineae cell envelope is the mycolyl-arabinogalactan (mAG) complex. The mAG is composed of lipid mycolic acids, and arabinofuranose (Ara) and galactofuranose (Gal) carbohydrate residues. Elucidating microbe-specific differences in mAG composition could advance biotechnological applications and lead to new antimicrobial targets. To this end, we compare and contrast galactan biosynthesis in and In each species, the galactan is constructed from uridine 5'-diphosphate-α-d-galactofuranose (UDP-Gal), which is generated by the enzyme UDP-galactopyranose mutase (UGM or Glf). UGM and the galactan are essential in but their importance in Corynebacterium species was not known. We show that small molecule inhibitors of UGM impede growth, suggesting that the galactan is critical in corynebacteria. Previous cell wall analysis data suggest the galactan polymer is longer in mycobacterial species than corynebacterial species. To explore the source of galactan length variation, a ortholog of the carbohydrate polymerase responsible for the bulk of galactan polymerization, GlfT2, was produced, and its catalytic activity was evaluated. The GlfT2 gave rise to shorter polysaccharides than those obtained with the GlfT2. These data suggest that GlfT2 alone can influence galactan length. Our results provide tools, both small molecule and genetic, for probing and perturbing the assembly of the Corynebacterineae cell envelope.