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Notes: Abstract Changes in mean style weight and in lysozyme activity of the style, digestive gland, gill and mantle of Mytilus edulis and Tellina tenuis from the Clyde Sea area, Scotland, were investigated over tidal cycles in March and August, 1981. For M. edulis, significant changes occurred in the style weight, style lysozyme activity and digestive gland lysozyme activity during a 22 h period. These appear to be related to a diurnal cycle rather than a tidal cycle. Changes in the weight of the style of M. edulis may be caused by dissolution during feeding, and style lysozyme may be secreted independently of the style matrix. The activity of lysozyme in T. tenuis is unaffected by the tide, suggesting that this intertidal bivalve can feed throughout the tidal cycle.

Notes: Abstract The uptake of several species of bacteria by the common mussel Mytilus edulis (L.) and the subsequent fate of some polymers of the bacteria have been investigated in a study carried out during 1981. Bacteria (Escherichia coli, Micrococcus luteus, M. roseus, Bacillus cereus, Staphylococcus aureus and a marine pseudomonad, 1-1-1) were radiolabelled by growth in medium containing 3H-thymidine and the uptake of bacteria by Mytilus edulis was monitored. Labelled and unlabelled bacteria, at initial concentrations of 0.5 to 1x107 bacteria ml-1, were cleared at similar, exponential rates with no significant difference in the rates for different bacteria: 90% of bacteria were cleared in a mean time of 1.93±0.12 h (SEM, n=63). Those bacteria with cell walls which were sensitive to M. edulis lysozyme were rapidly degraded by the mussel and 3H-labelled DNA was released in a form not precipitable by 10% trichloroacetic acid. Lysozyme-resistant bacteria (Micrococcus roseus and S. aureus) were cleared from suspension by Mytilus edulis but most were rejected intact. By measuring the rate of release of 3H-thymidine-labelled material from the mussel the rate of degradation of lysozyme-sensitive bacteria by M. edulis was found. For different bacteria the degradation rate varied from approx 2x108 to 27x108 bacteria h-1 with an overall mean of 10x108 bacteria h-1. A thymidine- and diaminopimelicacid-requiring auxotroph of E. coli was radiolabelled with 3H-thymidine, 3H-diaminopimelic acid or 14C-glucose and fed to M. edulis. Bacteria were cleared and degraded by the mussel; 3H-diaminopimelic acid-labelled or 14C-glucose-labelled polymers were retained, whereas 3H-thymidine-labelled polymers were released into the surrounding water. Extracts of the digestive gland of M. edulis degraded lysozyme-sensitive bacteria to release 3H-thymidine-labelled material, but did not release 3H-thymidine-labelled material from lysozyme-resistant bacteria. It is concluded that M. edulis can select lysozymesensitive bacteria for subsequent processing and discriminate between bacterial polymers to reject DNA. Also, bacteria could provide a substantial fraction of the carbon requirement of the mussel.