Electrochemical observations in microbiological processes. Growth of Thiobacillus thiooxidans. I

The growth of Thiobacillus Thiooxidans, utilizing sulfur in three media, was studied by observing changes in halfcell emf, bacterial cell count, and acid production, all as a function of time. A comparison of the biological halfcell emf with comparable control halfcells reveals that T. thiooxidans makes an electrochemical contribution to halfcell voltage. A change from the more complex medium of Skerman's mineral salts to ATCC allowed a clearer delineation of the ability of T. thiooxidans to make an electrochemical contribution. Reproducible biological halfcell emf's were obtained when the ferrous sulfate was removed from the ATCC medium. One halfcell, consisting of T. thiooxidans utilizing sulfur in ATCC, was observed over a 111‐day period. During this time, the initial halfcell voltage of −0.35 V. decreased to a value of −0.64 V. (hydrogen emf series). T. thiooxidans, in utilizing sulfur, produces only sulfate ion, thereby simplifying the identification of an electrochemical contribution during growth.