| Comments |
P.13 bottom paragraph:"Carbon: Organisms that obtain more than 50% of their carbon from CO2 alone are autotrophs. Organisms that obtain
less than 50% of their cellular carbon from CO2 are termed heterotrophs. The 50% threshold goes back to a long
discussion among microbiologists 30 years ago. Many bacteria synthesize cell constituents from CO2 and acetate, they obtain about 33% of their cell carbon from CO2, which might be a maximum for heterotrophs. There are also many carboxylation reactions in the biosyntheses of typical heterotrophs. For example, in both the purine and the pyrimidine ring, one carbon each comes from CO2, even in the de novo synthesis pathways of humans. When autotrophs have vitamin or amino acid auxotrophies, the 50% rule is very helpful." |