are recognized as important microbial systems, with high rates of
microbial activity and coupling. Understanding biofilm function has
broader ramifications into coastal engineering, biofouling and
cell-cell signaling. The diatoms are an important group of algae that
dominate many soft sediment aquatic habitats and produce large
amounts of extracellular polymeric substances (EPS) which consist
primarily of polysaccharide, proteoglycan and glycoproteins. EPS is
produced from all areas of the diatom cell, but has been most
intensively studied as related to diatom movement. Estuarine mudflat
diatoms reside in a thin biofilm approximately one millimeter thick
that harbors a variety of organisms, These biofilms are physically
stabilized by diatom EPS secretions produced during gliding motility.
Diatom migrations through the mud are rhythmic and entrained to tidal
and diel cycles and the various motility patterns exhibited by the
diatoms include gliding, reversals, pirouette, and corkscrewing.
objectives of this project are to relate changes in EPS production
and composition, diatom movement patterns, and switches in physiology
to environmental stimuli and to determine the pathways of diatom EPS
in carbon flow within estuarine biofilms. we are using a
combination of laboratory and field-based experiments to
identify particular characteristics of extracellular polymers that
represent responses to different environmental conditions (ex.
salinity stress) and those that may be correlated with distinct
diatom movement patterns. These modifications take the form of
production of distinct, new polymers or they may be realized though
additions of a small number of highly charged substituents (ex.
methyl groups, sulfate substitutions) on certain residues of the
polymers. The composition and structure of these different EPSs
influence the role such molecules play in the environment, through
changing their gelling and viscosity properties. Polymer structure
and properties also influence the degradation of EPS in the
fate of diatom EPS in the environment has been tracked using stable
isotope signatures combined with stable isotope labeling studies and
degradation sequences for key EPS types. This information is required
to define how diatoms acclimate to the changing conditions within
intertidal biofilms, to determine the nature of the different EPSs
produced, and the fate of the EPS material in the environment.