Biofilms 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.
      The continuing 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 environment.
      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.