MEPS 190:141-153 (1999)  -  doi:10.3354/meps190141

ABSTRACT: Starving and grown cultures of the heterotrophic, marine isolate FL2 were exposed to a defined flow at a hydrodynamically smooth, sandy sediment-water interface with a partially homogeneous bottom shear stress pattern but localized high advective inflow. Since transport-determining properties like cell size, hydrophobicity, motility and exopolymer production all change during 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 between starving and grown cells, calling into question the transfer of laboratory results from exponentially grown cultures to in situ conditions and generally the substitution of bacteria by particles in transport experiments. While microspheres were distributed according to the advective flow and only weakly retained by interactions with sediment particles, grown bacteria showed a spatially homogeneous distribution over the sediment surface. One suggestion is that active movement renders them independent of advective inflow once they have contact with the sediment. Starved cells, however, accumulated at the surface area of highest advective flow. They excreted exopolymers different from those in exponential phase, and, consequently, formed aggregates of up to 7 µm in diameter, which were then retained at the surface due to straining. If this accumulation turns out to be a widespread behaviour of copiotrophic bacteria, possible consequences--both ecological and also regarding pathogenic bacteria in coastal zones--have to be considered.

KEY WORDS: Transport into sediment · Starving bacteria · Microspheres · Exopolymers · Straining