Acid Production by the Escherichia-Aerobacter Group of Bacteria as Indicated by Dissolved Metallic Iron.

The present study had its origin in certain experiments carried on in our laboratory to determine the possible influence of metals on bacterial growth. It was observed that members of the Escherichia-Aerobacter group when cultivated in an unbuffered glucose broth containing iron filings produced sufficient acid to dissolve some of the iron. The dissolved iron was detected by means of the potassium ferrocyanide test. Since more acid is produced by Escherichia coli than by Aerobacter aerogenes from the same quantity of glucose, it was thought that it should be possible to add to the medium sufficient buffer to neutralize the acid produced by Aerobacter aerogenes, while that produced by Escherichia coli, under the same conditions, would still be sufficient to dissolve the iron. The investigation of this hypothesis was the purpose of the study here reported. A preliminary report has been published in abstract form (Syrocki and Fuller, 1935).