Film formation by marine bacteria at a model fluid interface

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