Radiolabeling of Treponema pallidum (Nichols virulent strain) in vitro with precursors for protein and RNA biosynthesis.

We observed uptake of [U-14C]serine, U-14C-labeled amino acid hydrolysates, and [2-14C]uracil by virulent Treponema pallidum in vitro for at least 96 h. No uptake of [2-14C]thymine, [1-14C]pyruvate, [U-14C]pyruvate, and [2-14C]uridine was detected. Treponemal protein and RNA biosynthetic activity was identified by erythromycin inhibition of amino acid and uracil uptake. Radioactivity due to uptake of radiolabeled amino acids by residual testicular cells in the cultures remained at background levels regardless of the presence or absence of cycloheximide. Accumulation of the radiolabeled substrates by T. pallidum proceeded at a linear rate for 48 to 96 h during incubation in vitro. The longevity of substrate uptake using the system of incubation described will facilitate future studies on the metabolism of the microorganism to help determine essential growth factors and environmental conditions for multiplication of T. pallidum in vitro.