Electrophoretic mobility of natural particles and cultured organisms in freshwaters1

Abstract

Electrophoretic mobility (EM) was measured on natural particles from 11 southeastern U.S. lakes and streams. The mobility decreased with increased conductivity, increased with dissolved organic carbon (DOC), and increased with pH. EM was further measured in each water sample with pH adjusted over the pH range 3–10. In general, mobility increased with pH, but particles in hard waters were only slightly affected, while particles in soft waters with high DOC showed a sharper rise in EM due to increase of pH. The experiments were repeated with the cyanobacterium Microcystis aeruginosa, the green alga Chlorella vulgaris, and the bacterium Klebsiella sp. in filtered water from several of the sites. Cultured cells showed greater homeostasis of EM in the pH gradient than the natural particles, but cells in soft water with high DOC had greater mobility than those in hard water. The three species differed in their mobility: Microcystis consistently had the highest EM and Chlorella the lowest; Chlorella was neutral in the hard waters. Klebsiella was intermediate in EM. The results indicate that individual habitats and particle species may represent different challenges to filter feeders, based on particle surface chemistry.