We have characterized the nonspecific interactions in the initial attachment and film formation by marine bacteria at a dynamic fluid interface: seawater/dropping mercury electrode. Experimental evidence is presented that bacteria readily establish molecular contact with the metal substrate without mediation of a conditioning film. Prevalence of hydrophobic over electrostatic interactions and the possible importance of Ca2+ bridging could be inferred. The attachment of individual bacterial cells is faster than their transport from the aqueous medium, as is the case in the transport-controlled adsorption of biopolymers. The cell aggregates yield distinct electrical attachment signals, allowing a comparison between cell-cell and cell-substrate affinities. The cell-cell interactions, as well as the interaction of cell aggregates with negatively charged substrate, were greatly enhanced in seawater compared to pure NaCl solutions. The model experiments point out that marine bacteria should represent a significant component of the initial film formed at freshly exposed surfaces in seawater. This was found to hold for bacterial strains whether they were initially isolated as attached or as free-living.
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