Effect of titanium (III) citrate as reducing agent on growth of rumen bacteria

We compared the growth of 10 strains of rumen bacteria in an anaerobic medium reduced with cysteine hydrochloride, dithiothreitol, or titanium (III) citrate. The redox potential of medium reduced with cysteine hydrochloride was -167.8 mV; with dithiothreitol it was -175.8 mV; and with titanium(III) citrate it was -302.4 mV at a concentration of 5 X 10(-4) M titanium and -403.9 mV at 2 X 10(-3) M titanium. Maximum growth of the strains was generally lower with dithiothreitol or titanium(III) citrate than with cysteine hydrochloride, although growth was greater than in medium lacking an added reducing agent. Strains for which cysteine was required or markedly stimulatory grew only poorly with titanium(III) citrate. No strain grew in medium with sodium citrate as the energy source. Titanium(III) citrate could be used to reduce anaerobic media for some rumen bacteria if the exclusion of a sulfur-containing reducing agent is required.