THE EFFECTS OF BACTERIA ON THE FLOW BEHAVIOR OF CLAY SEAWATER SUSPENSIONS

The presence of glue-like exopolymer produced by the marine benthic ba cterium Alteromonas atlantica present in concentrations comparable wit h typical marine muds can enhance the yield stress of dilute clay-seaw ater suspensions typical of the sediment-water interface by 60%. This effect is inferred to be due mainly to bacterial attachment to and exo polymeric bridging between clay domains under nutrient-poor conditions . The relative change in the yield stress of a clay-seawater suspensio n, and by inference its erosion resistance, is dependent on the availa bility of nutrients and the history of microbial attachment. This conc lusion applies regardless of the constitutive model used to describe t he behavior of the suspension under shear. Our results are relevant to rheological studies of fine-particle suspensions in general because i nevitable contamination of ''abiotic'' slurries often occurs under the very conditions (nutrient poor) that can result in maximal binding ef fects.