Nutritional, chemical and ultrastructural characterization of the lorica and extracellular mucilage of phacotus lenticularis (Phacotaceae, volvocales)

The nutrition, chemical composition and ultrastructure of the unicellular chlorophycean flagellate Phacotus lenticularis are investigated, with special emphasis on the lorica and extracellular mucilage. Cells of P. lenticularis are distinguished by the presence of a bivalved lorica, which can vary in size, shape and color depending upon culture conditions. Elemental analysis of isolated loricas with SEM-EDS reveals differences in dark and colorless loricas. Dark loricas have manganese as the principal element, whereas in colorless loricas, calcium is the predominant element. The presence of nitrogen in the medium influences both the size and elemental composition of the lorica. The lorica matrix is estimated to contain ca. 36% carbohydrate, 26% protein and 4% ester-linked sulfate, with the amino acid hydroxyproline accounting for ca. 1% of the protein. Chemically, the lorica is composed of a structural polymer of glucose, with a supporting acid mucopolysaccharide matrix.