Growth and metabolism of Aquaspirillum gracile

Several aspects of the growth and metabolism of Aquaspirillum gracile ATCC 19624 were investigated including its relationship to oxygen, ability to grow on defined media, and carbohydrate catabolism.

Although previously reported to be microaerophilic, A. gracile was demonstrated to be aerobic by comparing growth responses in varying concentrations of oxygen. A defined medium for the growth of A. gracile ATCC 19624 was developed which contained mineral salts, succinate, glutamine, leucine, phenylalanine, aspartate, and biotin. Biotin appeared to be an essential growth requirement.

A. gracile is one of the few spirilla that yield acid reactions from sugars, but its sugar catabolism has not been previously investigated. Only D-glucose, D-galactose, and L-arabinose are attacked. The soluble portion of extracts of glucose-grown cells was found by spectrophotometric methods to contain enzyme activities characteristic of the Entner-Doudoroff and the Embden-Meyerhof-Parnas pathways. Much lower specific activities occurred in succinate-grown cells. No activity for 6-P-gluconate dehydrogenase was detected. Inducible dehydrogenase activities for arabinose and galactose occurred in cells cultured on either sugar. Glucose-grown cells contained not only glucokinase and glucose-6- p dehydrogenase activities but also glucose dehydrogenase activity. Gluconate dehydrogenase activity was not detected but gluconate kinase activity was present, Paper chromatographic analysis of the spent culture supernatants from glucose-grmm cells indicated an accumulation of gluconic acid and this hypothesis was confirmed by a more specific enzymatic assay for gluconate. Preliminary evidence is presented for the accumulation of galactonic and L-arabonic acids in galactose and L-arabinose cultures, respectively.