Arch. Mikrobiol. 86, 1--12 (1972) 9 by Springer-Verlag 1972 Carbon Utilization Patterns in the Heterotrophic Blue-Green Alga Chlorogloea fritschii J. S. MILLm~ and M. M. ALLEN Department of Biological Sciences, Wellesley College, Wellesley, Mass. 02181, U.S.A. Received May 15, 1972 Summary. 1. The metabolic patterns of Chlorogloea ]ritschii, a blue-green alga capable of growing both heterotrophically and autotrophically, were analyzed in cells grown with different carbon and energy sources. 2. The distribution of isotopic carbon incorporated into ceils grown on com- binations of CO2, sucrose and acetate in the light or in the dark was determined after cell fractionation and amino acid isolation. Fractionatiou studies indicated that C./ritschii utilizes organic substrates both in the light and the dark, but that the pattern of incorporation in the light is more similar to that seen in other blue- green algae grown in the light than to its own pattern in the dark. 3. C02 is also incorporated into both light-and dark-grown cells, but sucrose is the preferred substrate when C02 and sucrose are both present. 4. Label from radioactive sucrose and acetate was distributed into all amino acids separated. Large amounts of label appeared in both the glutamate and aspar- tare families, suggesting that the Krebs cycle, which appears to be incomplete in other blue-greens, may be fully functional in C./ritschii in the light and in the dark. Although blue-green algae have been shown to flourish in soils and waters rich in organic nutrients, they have long been considered obhgate autotrophs incapable of assimilating or utilizing, except to a very limited degree, any carbon source other than CO, (Holm-Hansen, 1968; Itoare et al., 1967; Pearce and Carr, 1969; Smith et al., 1967; Wfldon and Ap Rees, 1965). A recent survey study by Khoja and Whitton (1971) has shown that at least 17 strains of blue-greens are capable of heterotrophic growth. These strains share the common characteristics of being filamen- tous and of having an abundant sheath layer. The strains used in most previous studies of blue-green algal physiology and structure were unicellular organisms since filamentous strains are more difficult to work with. Chlorogloea/ritschii, a filamentous blue-green alga, has been shown to grow well as a photoautotroph, as a photoorganotroph utilizing sucrose in the light, and as a chemoorganotroph (Fay, 1965). Growth in the light i Arch. Mikrobiol,, Bd, 86