Although it is unlikely that SinR
senses oxygen directly, its expression is activated under
oxygen limitation.
A. tumefaciens with a sinR disruption
formed a sparse, heterogeneous biofilm on abiotic surfaces,
whereas strong sinR expression resulted in much
thicker and less structured biofilms.
The sinR biofilm phenotypes were recapitulated when examined on plant
roots.
Surface boundary layers and biofilms are generally
oxygen-limited, and we speculate that SinR functions to
respond to this feature of surface-associated growth.
Other bacteria also appear to experience oxygen limitation
during plant association [43,44].