Vanillin cultures of Clostridium formicoaceticum produced higher cell
densities than did vanillate cultures. During growth at the expense of
vanillin, vanillate was the predominant intermediate formed; 3,4-dihy
droxybenzaldehyde was not a significantly detectable intermediate. Ace
tate and protocatechuate were both produced in equimolar ratio relativ
e to vanillin consumption. 4-Hydroxybenzaldehyde was a growth-supporti
ve aromatic compound for both C. formicoaceticum and Clostridium aceti
cum (doubling times approximated 5 h), was oxidized stoichiometrically
to 4-hydroxybenzoate, and was not appreciable toxic at concentrations
up to 15 mM. Acetate was (i) the major reduced end product detected c
oncomitant to growth and to benzaldehyde oxidation and (ii) formed in
close approximation to the following stoichiometry : 4 4-hydroxybenzal
dehyde + 2 CO2 + 2H2O --> 4 4-hydroxybenzoate + CH3COOH. We conclude t
hat these two acetogens are capable of benzaldehyde-coupled acetogenes
is and growth.