f cellulose, which is produced by Gluconacetobacter xylinus, or
heteropolysaccharides. Examples of the latter include the CPS
produced by Acetobacter tropicalis SKU1100 [consisting of glucose,
galactose and rhamnose (1)] or that of Acetobacter aceti (reclassified
as Acetobacter pasteurianus subsp. Lovaniensis), consisting of
glucose and rhamnose (2).
A genetic study on the pellicle polysaccharide produced by
A. tropicalis SKU1100 showed that a gene cluster, polABCDE, is
required for pellicle formation; polB is involved in the production of
dTDP-rhamnose, while polE is involved in anchoring the polysaccharide
to the cell surface (3). Disruption of the polE gene
resulted in no pellicle formation in static culture due to the absence
of CPS production. Instead, this mutant strain secretes EPS with the
same sugar composition into the culture medium. Further, the galE
gene that encodes UDP-galactose 4-epimerase was identified to be
involved in UDP-galactose biosynthesis in A. tropicalis SKU1100 (4).
Previous studies reported that A. pasteurianus IFO3284 produces
two different types of colony: a rough-surfaced colony (R strains)
that can produce a pellicle and a smooth-surfaced colony (S strain)
that cannot produce a pellicle in static culture. The R and S strains
are inter-convertible by spontaneous mutation (5). According to
Kanchanarach et al. (6), the R strain of different A. pasteurianus
strains gave higher acetic acid production, whereas the S strains
could not complete the fermentation. This suggests that the R
strains (with pellicle polysaccharide) have higher acetic acid