Die organiese voeding van drie algsoorte van die Belmontrivier naby Grahamstad

Abstract

The diatom Achnanthes pseudohungarica is capable of utilizing urea and a large number of amino acids as its only sources of nitrogen. This. diatom can also assimilate and utilize urea and a large number of amino acids and sugars as its only sources of carbon. None of these substances could, however, support the growth of this organism in the dark, or stimulate its growth under conditions where light was a limiting factor. Although acetate, glutamic acid and phenylalanine were found to be assimilated by the diatom Nitzschia palea in the dark, and to stimulate the growth of this organism under conditions where light was a limiting factor, nevertheless none of these substances could support the growth of this organism in the dark. Various attempts were made to determine the cause of the obligate phototrophy in Nitzschia palea and Achnanthes pseudo-

hungarica by comparing various aspects of the metabolism of these organisms with that of a Scenedesmus-specie, which is capable of heterotrophic growth. There seems to be no significant synthesis of new cellular material in Nitzschia palea in the absence of photosynthesis and in the simultaneous presence of organic substrates. This is reflected by the fact that cells which have been kept in the dark for more than a week assimilated organic substrates as oil drops which would normally constitute the reserve material of this organism. For the inability of Achnanthes pseudohungarica to grow in the dark in the simultaneous presence of organic substrates which, moreover, it can assimilate , no other explanation can be given than that light is required for its growth. Nitzschia palea grew equally well in the presence of organic substrates and in an inorganic culture solution where ample co was supplied. This suggests that the ;a presence of this organism in sewage-polluted water is not only the result of its ability to utilize organic substrates as sources of nitrogenp carbon and energy, but also that its ability to grow actively under these conditions is equally important. The importance of Achnanthes pseudohungarica in the purification of sewage-polluted water is reflected by the ability of this organism to oxidize a large number of organic substrates.