Amino Acid assimilation and electron transport system activity in attached and free-living marine bacteria

Amino acid assimilation and electron transport system activity of a marine Pseudomonas sp. was evaluated to determine whether the activity of bacteria attached to solid surfaces differed from that of free-living bacteria or bacteria which had been attached but subsequently desorbed from the substratum (detached bacteria). Bacteria were allowed to attach to glass and to a range of plastic surfaces (Thermanox, polyvinylidene fluoride, polyethylene, polytetrafluoroethylene). Microautoradiography and staining with a tetrazolium salt to demonstrate electron transport system activity were used to compare the activity of these organisms with that of free-living or detached cells. The water-wettability of the surfaces was evaluated by measuring the advancing contact angle (theta(A)) of water on each surface, to determine whether there was a relationship between activity and substratum hydrophilicity. There was an increase in the proportion of leucine-assimilating attached bacteria and in the proportion of attached cells demonstrating electron transport system activity with an increase in substratum theta(A), but the relationship between activity of attached and free-living cells depended on the substratum. Activity appeared to promote firm attachment, and detached bacteria assimilated fewer amino acids than did attached cells. There was no general effect of surfaces on attached bacterial activity, and attached cells may be more, or less, active than free-living cells, depending on the amino acid, its concentration, and substratum properties.