Influence of the physiological status of bacteria on their transport into permeable sediments

Starving and grown cultures of the heterotrophic, marine isolate FL2 were e xposed to a defined flow at a hydrodynamically smooth, sandy sediment-water interface with a partially homogeneous bottom shear stress pattern but loc alized high advective inflow. Since transport-determining properties like c ell size, hydrophobicity, motility and exopolymer production all change dur ing starvation, we compared the distribution of differently nourished cells and microspheres at the surface and in the sediment after 3 d of exposure. We found different sorting processes between particles and bacteria, and b etween starving and grown cells, calling into question the transfer of labo ratory results from exponentially grown cultures to in situ conditions and generally the substitution of bacteria by particles in transport experiment s. While microspheres were distributed according to the advective flow and only weakly retained by interactions with sediment particles, grown bacteri a showed a spatially homogeneous distribution over the sediment surface. On e suggestion is that active movement renders them independent of advective inflow once they have contact with the sediment. Starved cells, however, ac cumulated at the surface area of highest advective flow. They excreted exop olymers different from those in exponential phase, and, consequently, forme d aggregates of up to 7 mu m in diameter, which were then retained at the s urface due to straining. if this accumulation turns out to be a widespread behaviour of copiotrophic bacteria, possible consequences-both ecological a nd also regarding pathogenic bacteria in coastal zones-have to be considere d.