FIG. 1.

Biosynthetic genes and structures of repeating units for xanthan gum (14), rhizobial EPS (31), and sphingans S-88 (15), S-198 (4), and NW11 (23). Acetyl, pyruvyl, and hydroxybutanoyl groups are not shown. The reducing end of each repeat is to the right, and the IPP carrier is attached through a phosphodiester linkage at the reducing end. The order of sugars attached to IPP for the sphingans and the corresponding biosynthetic genes were inferred from the genetic and biochemical experiments reported here for strain S88. Gal, galactose; Man, mannose; Rha, rhamnose.