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Appl Environ Microbiol. 1974 March; 27(3): 549-552
Copyright © 1974 American Society for Microbiology. All Rights Reserved.

Sodium, an Obligate Growth Requirement for Predominant Rumen Bacteria¹

^a Division of Microbiology and Veterinary Medicine, University of Wyoming, Laramie, Wyoming 82071

ABSTRACT

Sodium is an obligate growth requirement for most currently recognized predominant species of rumen bacteria. The isoosmotic deletion of Na⁺ from a nutritionally adequate defined medium completely eliminated growth of most species. Growth yields and rates were both a function of Na⁺ concentration for Na⁺-requiring species, and Na⁺ could not be replaced by Rb⁺, Li⁺, or Cs⁺ when these ions were substituted for Na⁺ at a concentration equivalent to an Na⁺ concentration that supported abundant growth. Li⁺, Cs⁺, or Rb⁺ was toxic at an Na⁺-replacing concentration (15 mM) but not at a K⁺-replacing concentration (0.65 mM). K⁺ was also an obligate growth requirement for rumen bacteria in media containing Na⁺ and K⁺ as major monovalent cations, but K⁺ could be replaced, for most species, by Rb⁺. The quantities of Na⁺ that support rapid and abundant growth of Na⁺-requiring rumen bacteria show that these organisms are slight halophiles. A growth requirement for Na⁺ appears more frequent among nonmarine bacteria than has been previously believed.

² Present address: Department of Bacteriology, University of California at Los Angeles, Los Angeles, Calif. 90024.

¹ Wyoming Agricultural Experiment Station journal article 614.