Like R. Palmer I doubt whether the soil is as dry all the time as is
implied. What about the diurnal variation and nocturnal moisture in
many environments? That might provide enough moisture for some
bacterial growth. If they then synthesise exopolysaccharide they can
surround themselves with a very hydrophilic environment which can
provide a protective film within which there remains a sufficiently
high humidity for the cells to survive. recent work by Kevin Hughes
working here has shown the great difference in survival between EPS
plus and EPS minus strains during deisccation.
Another point about the soil and also leaf surfaces is the common
finding of Myxobacteria as microcolonies. Surely an example of a
monospecies biofilm! Any ideas on these? Ian Sutherland.