Superoxide imposes leakage of sulfite from Escherichia coli

Escherichia coli, which lacks the cytosolic superoxide dismutases, exhibits several nutritional auxotrophies when growing aerobically. The cysteine/methionine requirement, which is one of these, was previously shown to be due to leakage from the cells, and accumulation in the medium, of a metabolic intermediate on the biosynthetic route to these amino acids. The parental strain does not significantly accumulate this compound. It is now shown that treatment with alkaline cyanide releases sulfite from this compound, a property shared by alpha-hydroxy sulfonic acids (carbonyl-bisulfite adducts). Since E. coli accumulates carbonyl compounds in the growth medium, it appears likely that the sulfitogenic compounds accumulated by the sodA sodB strain are alpha-hydroxy sulfonic acids.