Filtration and Utilization of Laboratory-Cultured Bacteria by Dreissena polymorpha, Corbicula fluminea, and Carunculina texasensis.

Dreissena polymorpha consumed about 6 x 108 Escherichia coli from 20 ml of artificial pondwater (APW) in 30 min under laboratory conditions. The clearance rate per mussel was 143 +/- 25 ml g-1 dry tissue min-1. The E. coli used in these studies ranged from about 1.7 to 2.9 {mu}m in length. 35S-labeled E. coli were used to demonstrate that bacteria-derived nutrients were incorporated into mussel tissue. Electrophoretic analysis of mussel and bacterial proteins on 12% polyacrylamide gels allowed the visual determination of incorporation of labeled amino acids into bivalve proteins and demonstrated that intact bacteria were not simply trapped in mussel tissues. The conversion of bacterial-labeled amino acids into mussel protein was about 26%. Similarly, we demonstrated that D. polymorpha can use other bacterial species ranging in size from about 1.3 to 4.1 μm, including Citrobacter freundii, Enterobacter aerogenes, Serratia marcescens, Bacillus megaterium, and B. subtilus. The ability of D. polymorpha to take up E. coli was compared with that of two other freshwater mussels, Corbicula fluminea and Carunculina texasensis. On a mussel-dry-weight basis, D. polymorpha cleared bacteria 30 to 100 times faster than Corbicula fluminea and Carunculina texasensis, respectively. The ability to filter E. coli appears to be related to the architecture of the cirri on the latero-frontal cells of the gill. Cirri from Corbicula and Dreissena are similar in size, but Dreissena has a larger gill compared to the tissue dry-weight, and has 102 times more cirri than found in Corbicula. Carunculina, the unionid representative, has smaller and fewer cirri, and has relatively limited ability to capture E. coli.