Table 3. Comparison of nutrients that are shared in microbial communities, highlighting the qualities of cobamides as a model system.

Filled circles indicate that a class of metabolites has a particular feature; half-filled circles indicate that a subset of the metabolites have the corresponding feature.

FEATURES	AMINO ACIDS	NUCLEOTIDES	ORGANIC COFACTORS	COBAMIDES
Evidence for widespread sharing	●	●	●	●
Well-characterized biosynthesis	●	●	●	●
Distinctive spectral features and colors			◐	●
Effective in small quantities (catalytic)			●	●
Structurally diverse			◐	●
Most are commercially available	●	●	●