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COMBINATION OF DITHIOTHREITOL AND SULFIDE AS REDUCTANTS IN NITROGEN-FREE MINIMAL MEDIA FOR GROWTH OF ANAEROBIC RUMINAL BACTERIA AND PREVOTELLA RUMINICOLA STRAIN B14 ON AMMONIA
Authors:S.C. RICKE  D.M. SCHAEFER
Affiliation:Department of Poultry Science Texas A&M University College Station, TX 77843–2472;Departments of Animal Science and Bacteriology University of Wisconsin Madison, WI 57606
Abstract:Cysteine is commonly employed as the medium reductant for ruminal bacteria, but many ruminal bacteria can use cysteine as a source of nitrogen as well as sulfur. The objective of the present study was to test a combination of dithiothreitol and sulfide as possible reductant substitutes for cysteine in anaerobic media containing ammonia as the nitrogen source. The type of reductant (cysteine versus dithiothreitol-sulfide) and ammonia concentration did not alter growth rates of Prevotella ruminicola strain B,4 (P>0.15). However, growth rates in dithiothreitol-sulfide reduced media varied tremendously between individual organisms ranging from 0.10 h−1 for Ruminococcus flavefaciens to 1.6 h−1 for Streptococcus bovis grown in 1 mM NH3-N. At both 1 and 11 mM NH4Cl, Str. bovis strain JB1 exhibited the greatest growth rate followed by Str. bovis strain C277. Megasphaera elsdenii strain T81 and Ruminococcus flavefaciens strain FD1 had the lowest growth rates at both NH4Cl concentrations. Increasing NH4Cl concentration from 1 to 11 mM resulted in increased growth rates for Ruminobacter amylophilus strains H18 and 70 and Str. bovis strain C277 (P<0.05), and decreased growth rates for S. ruminantium subsp. lactilytica strain HD4 and Str. bovis strain JB1 (P<0.01). These results indicate that dithiothreitol and sulfide can be combined as reductants in nitrogen-free basal media for most ruminal bacterial species.
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