Effect of Extreme Salt Concentrations on the Physiology and.pdf

JOURNAL OF BACTERIOLOGY, JUlY 1988, p. 3065-3071 Vol. 170, No. 7 0021-9193/88/073065-07$02.00/0 Copyright X 1988, American Society for Microbiology Effect of Extreme Salt Concentrations on the Physiology and Biochemistry of Halobacteroides acetoethylicus S. RENGPIPAT,t S. E. LOWE, AND J. G. ZEIKUS* Michigan Biotechnology Institute, Lansing, Michigan 48909, and the Departments ofBiochemistry and Microbiology, Michigan State University, East Lansing, Michigan 48824 Received 31 December 1987/Accepted 11 April 1988 Halobacteroides acetoethylicus grew in media with 6 to 20% NaCl and displayed optimal growth at 10% NaCl. When grown in medium with an [NaClI] of 1.7 M, the internal cytoplasmic [Na+] and [Cl-] were 0.92 and 1.2 M, respectively, while K+ and Mg2e concentrations in cells were 0.24 and 0.02 M, respectively. Intracellular [Na+] was fourfold higher than intracellular [K+]. Since Na+ and ClF ions were not excluded from the cell, the influence of high salt concentrations on key enzyme activities was investigated in crude cell extracts. Activities greater than 60% of the maximal activity of the following key catabolic enzymes occurred at the following [NaCl] ranges: glyceraIdehyde-3-phosphate dehydrogenase, 1 to 2 M; alcohol dehydrogenase (NADlinked), 2 to 4 M; pyruvate dehydrogenase, 0.5 to 1 M; and hydrogenase (methyl viologen linked), 0.5 to 3 M. These studies support the hypothesis that obligately halophilic, anaerobic eubacteria adapt to extreme salt concentrations differently than do halophilic, aerobic eubacteria, because they do not produce osmoregu- lants or exclude CF-. This study also demonstrated th