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Appl Environ Microbiol, March 1998, p. 976-981, Vol. 64, No. 3
0099-2240/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.

Relationship between Intracellular Phosphate, Proton Motive Force, and Rate of Nongrowth Energy Dissipation (Energy Spilling) in Streptococcus bovis JB1

Daniel R. Bond1 and James B. Russell2,*

Section of Microbiology, Cornell University,1 and Agricultural Research Service, U.S. Department of Agriculture,2 Ithaca, New York 14853

Received 22 September 1997/Accepted 7 January 1998

When the rate of glucose addition to nongrowing Streptococcus bovis cell suspensions was increased, the fermentation was homolactic, fructose-1,6-diphosphate (FDP) increased, intracellular inorganic phosphate (Pi) declined, and the energy-spilling rate increased. ATP and ADP were not significantly affected by glucose consumption rate, but the decrease in Pi was sufficient to cause an increase in the free energy of ATP hydrolysis (Delta G'p). The increase in Delta G'p was correlated with an increase in proton motive force (Delta p). S. bovis continuous cultures (dilution rate of 0.65 h-1) that were provided with ammonia as the sole nitrogen source also had high rates of lactate production and energy spilling. When Trypticase was added as a source of amino acids, lactate production decreased; a greater fraction of the glucose was converted to acetate, formate, and ethanol; and the energy-spilling rate decreased. Trypticase also caused a decrease in FDP, an increase in Pi, and a decrease in Delta p. The change in Delta p could be explained by Pi-dependent changes in the Delta G'p. When Pi declined, Delta G'p and Delta p increased. The ratio of Delta G'p to Delta p (millivolt per millivolt) was always high (>4) at low rates of energy spilling but declined when the energy-spilling rate increased. Based on these results, it appears that Delta p and the energy-spilling rate are responsive to fluctuations in the intracellular Pi concentration.

* Corresponding author. Mailing address: Wing Hall, Cornell University, Ithaca, NY 14853. Phone: (607) 255-4508. Fax: (607) 255-3904. E-mail: jbr8{at}cornell.edu.




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Copyright © 1998 by the American Society for Microbiology. All rights reserved.