Uptake and processing of cultured microorganisms by bivalves

Abstract

Escherichia coli Migula (Castellani & Chalmers), radiolabelled in different cellular polymers by growth in media containing [ 3H]thymidine, [ 14C]glucose or [ 3H]diaminopimelic acid, were fed to Mytilus edulis L. for 1 h to determine the rate of processing of different radiolabels over the ensuing seven days and the residence time in the digestive gland, mantle, gill, and body of the mussel. Each radiolabel was initially found predominantly in the digestive gland but was soon distributed elsewhere, particularly to the mantle. Mytilus exhibited discrimination in the storage of bacterial components in that ≈90% of 3H-radiolabelled material from [ 3H]diaminopimelic acid-labelled bacteria remained associated with the mussel after 7 days whereas from [ 3H]thymidine-labelled bacteria most of the radiolabel was rapidly released into the water. From 14C-labelled bacteria, carbon was processed and gradually respired as 14CO 2. Digestion of bacteria appeared to be initiated extracellularly in the stomach and to be completed intracellularly in the digestive gland of Mytilus. Of the bivalves examined ( Arctica islandica (L.), Cerastoderma edule (L.), Chlamys opercularis (L.), Mya arenaria L., Mytilus edulis and Ostrea edulis L.) for their ability to remove bacteria from axenic suspension in sea water, only Chlamys opercularis was unable to do so, although it could when the bacteria were in a mixed suspension with the alga, Tetraselmis suecica (Kylin) Butcher. The presence of T. suecica also increased the filtration rates of Mytilus and Ostrea edulis for bacteria. The rate at which bivalves degraded susceptible bacteria was largely dependent on filtration rate.