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POLYSACCHARIDE RELEASE BY APHANOTHECE HALOPHYTICA INHIBITS CYANOBACTERIA/CLAY FLOCCULATION1

Authors


  • 1

    Received 6 February 2009. Accepted 18 November 2009.

Abstract

Many microalgae release polysaccharides, but the effects of the polysaccharides on mutual flocculation of microalgae and clay in aquatic environments have not been well studied. Aphanothece halophytica Frémy is a bloom-forming cyanobacterium in salterns and can release large amounts of polysaccharide (AH-RPS). In the present study, we investigated the effect of AH-RPS on mutual flocculation of cyanobacterium and clay and further explored the mechanisms by which AH-RPS affected mutual flocculation. We determined that AH-RPS possessed clay-dispersing activity as defined as the ability to inhibit the flocculation and sedimentation of clay suspensions in water. Supplementation of AH-RPS in cyanobacterial cell suspensions and in the culture media containing the same kaolin clay concentration dose dependently decreased flocculation of cyanobacterial cells and increased clay-dispersing activity. These findings indicate that the clay-dispersing activity of AH-RPS was related to its inhibitory effect on mutual flocculation of cyanobacterial cells and clay particles. Moreover, the clay-dispersing activity of AH-RPS was stable from pH 3 to pH 10 and was increased by adding NaCl, MgCl2, CaCl2, or low concentrations of KCl (up to 0.4 M). Taken together, our data suggest that AH-RPS might maintain its clay-dispersing activity and inhibit mutual flocculation of microalgae and suspended clay in saltern brine.

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