FIG. 1.

Formation of acetate (○), formate (●), and CH₄ (□) from H¹⁴CO₃⁻ in gut homogenates of C. orthognathus under N₂-CO₂ atmosphere (A), under H₂-CO₂ atmosphere (B), or under N₂-CO₂ atmosphere in the presence of 5 mM unlabeled formate (C). Values are means of two replicate assays. In the case of acetate, it was assumed that both C atoms stemmed from CO₂. Similar results were obtained for C. umbratus (Table 1).