The Unilinear Transmission of Motility and its Material Basis in Salmonella

SUMMARY: Certain sub-lines of a strain of Salmonella paratyphi C contain 10 % or more of motile flagellated bacteria when in exponential growth at 37°. Less than 0-1% of the organisms are motile after prolonged exponential growth at 20°. Single motile organisms isolated from cultures grown at 37° transmitted motility to only one or a few of their descendants during growth at 20°; they behaved as if their motility were due to non-multiplying motility-conferring (MC) particles. There is a good correlation between the distributions of number of MC particles/motile bacterium as indicated by the numbers of motile descendants at 20°, and the distributions of number of flagella/flagellated bacterium in stained preparations. It is inferred that one MC particle corresponds to one flagellum. The results support the hypotheses that in some cases flagella arise as a consequence of discontinuous intracellular events, each of which leads to the synthesis of a small number of flagella, and that parental flagella are shared amongst progeny bacteria until no descendant has more than one flagellum derived from a parental cell several generations removed. This sharing is not detected unless synthesis of new flagella ceases whilst bacterial growth continues. Single flagella may be unilinearly transmitted for over 20 generations.