Biosynthesis of vitamin B6 by bacteria.

The biosynthesis and control of vitamin B6 in bacteria could be studied more easily if an organism which produced large amounts of this family of compounds could be found. Unfortunately, the measurements of bacterial vitamin B6 that have been reported have often failed to include the total extracellular vitamin B6, and thus they do not adequately reflect the total vitamin B6 in the whole culture. Consequently, the total vitamin B6 content of cultures of bacteria freshly grown in simple defined media has been measured to allow a comparison of their abilities to synthesize this vitamin. All identified bacteria were isolated before use from stocks obtained from either the American Type Culture Collection or the Department of Bacteriology, University of Florida. The measurement method for total vitamin B6 (pyridoxine) in bacterial cultures has been described (W. B Dempsey, J. Bacteriol. 90:431, 1965). Except for Thiobacillus thiooxidans, Streptomyces griseus, and Achromobacter xerosis, all data reported in Table 1 were obtained with samples withdrawn within one doubling time after the cultures reached stationary phase. The three exceptions had samples withdrawn within 24 hr after growth had stopped. T. thiooxidans cultures were filtered through coarse filter paper to remove sulfur particles before either optical density measurements or samples were taken. Dry weights were determined by drying to constant weight, at 110 C, duplicate, washed samples of bacteria containing a minimum of 15 mg each (dry weight). In addition to the identified organisms, 23 unidentified organisms from soils of widely scattered origin were tested after primary isolation on a glucose plus salts-agar seeded with Escherichia coli B-B6-53. This pyridoxineless mutant and the method of seeding it have been described (W. B. Dempsey and P. F. Pachler, J. Bacteriol. 91:642, 1966). The organisms used were those which retained the combined abilities to grow on a minimal medium and to cross-feed the seeded mutant after isolation in pure culture. When grown in medium A (Table 1), 19 of the organisms had vitamin B6 contents in the range 60 to 80 ng/mg. The remaining four organisms had higher amounts of vitamin B6, and these TABLE 1. Total vitamin B6 content in bacterial cultures