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Aerotaxis (migration towards oxygen) of Bacillus cereus M63, a motile strain, was inhibited by potassium cyanide and 2-heptyl-4-hydroxyquinoline N-oxide, indicating a requirement for both the terminal oxidase (cytochrome aa3) and the cytochrome b segment of the electron transport system. The concentration of oxygen that gave a half-maximal aerotactic response (K0.5) was 0.31 microM, which was similar to the Km for respiration (0.80 microM). The proton motive force increased from -135 to -177 mV when anaerobic cells were aerated, and it is proposed that the signal for aerotaxis is the increase in proton motive force that results from increased respiration. A strain of B. cereus T initially used in this study was immotile, grew as long chains of cells, and was deficient in autolytic enzyme. B. cereus M63 is a spontaneous derivative of B. cereus T that has normal motility.

Cytochrome o was the only oxidase of the electron transport system that was present in exponentially growing Salmonella typhimurium ST1. Identification of cytochrome o was made by the (CO-reduced)-minus-(reduced) difference spectra and by the photochemical action spectrum of the relief, by light, of CO-inhibited respiration. Cytochrome o also functioned as the receptor for chemotaxis to oxygen (aerotaxis). The concentration of oxygen that elicits the maximum response for aerotaxis (0.7 microM) was similar to the Km for respiration (0.74 microM), and both aerotaxis and respiration were blocked 5 mM KCN.

Sensory transduction in aerotaxis required electron transport, in contrast to chemotaxis, which is independent of electron transport. Assays for aerotaxis were developed by employing spatial and temporal oxygen gradients imposed independently of respiration. By varying the step increase in oxygen concentration in the temporal assay, the dose-response relationship was obtained for aerotaxis in Salmonella typhimurium. A half-maximal response at 0.4 microM oxygen and inhibition by 5 mM KCN suggested that the "receptor" for aerotaxis is cytochrome o. The response was independent of adenosine triphosphate formation via oxidative phosphorylation but did correlate with changes in membrane potential monitored with the fluorescent cyanine dye diS-C3-(5). Nitrate and fumarate, which are alternative electron acceptors for the respiratory chain in S. typhimurium, inhibited aerotaxis when nitrate reductase and fumarate reductase were induced. These results support the hypothesis that taxis to oxygen, nitrate, and fumarate is mediated by the electron transport system and by changes in the proton motive force. Aerotaxis was normal in Escherichia coli mutants that were defective in the tsr, tar, or trg genes; in S. typhimurium, oxygen did not stimulate methylation of the products of these genes. A cheC mutant which shows an inverse response to chemoattractants also gave an inverse response to oxygen. Therefore, aerotaxis is transduced by a distinct and unidentified signally protein but is focused into the common chemosensory pathway before the step involving the cheC product. When S. typhimurium became anaerobic, the decreased proton motive force from glycolysis supported slow swimming but not tumbling, indicating that a minimum proton motive force was required for tumbling. The bacteria rapidly adapted to the anaerobic condition and resumed tumbling after about 3 min. The adaptation period was much shorter when the bacteria had been previously grown anaerobically.

Tumor growth-inhibiting substances are demonstrated in various grains with the aid of a rapid test on Sarcoma 180. They are effective by feeding in combination with injections of a standard solution of yeast extracts. Extracts of these grains are effective upon intravenous injection.

In 8 out of 33 treated mice complete regressions of spontaneous breast adenocarcinomas were effected with intravenous and subcutaneous injections of yeast extract.