In this study we have revealed that PEG-degrading
sphingomonads possess an operon responsible for degradation
of this high-molecular-mass synthetic polymer. This is
believed to be the first report on the structure of the peg
operon and its distribution among sphingomonads. The
operon consists of PEG-degradative genes and a putative
PEG-translocating system, as well as its regulatory machinery.
Since industrial PEG utilization started about 30 years
before the isolates were found, these sphingomonads have
been able to evolve this xenobiotic-degradative operon. Very
possibly, transposases and conjugative plasmids have
permitted the organization of the operon from existing
sources. The constitutive expression of PEG-DH in strain
203 alone is explained by the genetic structure of the operon
in this strain. The complete sequencing of the large plasmids
and comparison of their structure with that of related
plasmids will reveal the evolution and origin of the operon,
as well as the reasons for the differences of substrateuptake
specificity and symbiosis among PEG-degrading
sphingomonads.