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Sodium and Other Inorganic Growth Requirements of Bacteroides amylophilus¹

^a Division of Microbiology and Veterinary Medicine, University of Wyoming, Laramie, Wyoming 82070, and Department of Dairy Science, University of Maryland, College Park, Maryland 20742

ABSTRACT

Bacteroides amylophilus has growth requirements for Na⁺, PO₄^3–, K⁺, and small quantities of Mg²⁺. No requirement could be shown for Ca²⁺ in media previously found growth-yield-limiting for Bacteroides succinogenes. Deletion of Co²⁺, Mn²⁺, Cl^–, or SO₄^2– did not affect growth. Quantitative studies indicate that Na⁺, K⁺, and PO₄^3– have differing effects on the growth of B. amylophilus. A concentration of sodium and potassium ions affects both growth rate and growth yield, whereas a phosphate concentration markedly affects growth yield, but affects growth rate only slightly, if at all. The sodium requirement of B. amylophilus is absolute. It cannot be replaced by K⁺, Li⁺, Rb⁺, or Cs⁺. The latter three monovalent cations are toxic to B. amylophilus if supplied to the organism at Na⁺-replacing concentrations. K⁺ is inactive at similar concentrations. The K⁺ requirement of B. amylophilus may be satisfied by Rb⁺. The concentration of Na⁺ required by B. amylophilus for abundant growth suggests that B. amylophilus should be considered a slightly halophilic organism. The results suggest that Na⁺ may be a more frequent requirement among terrestial bacteria obtained from relatively low-salt environments than has been previously believed.

¹ Journal Paper No. 466 of the Wyoming Agricultural Experiment Station.