The effect of tunicamycin on wall-polymer synthesis in Bacilli.

tion of incorporation into the hot-SDS-insoluble fraction was 55% at 100pg of tunicamycin/ml, and higher concentrations had no greater effect. Again, the resistant 45% would appear to reflect the presence in the cells of partially synthesized teichuronic acid already inacessible to the action of tunicamycin. In the trichloroacetic acid-precipitated fraction, however, whereas the maximum inhibition was 60% at 5Opg of antibiotidml, higher drug concentrations steadily increased the observed incorporation until at 500pg/ml the residual inhibition was only 6% (Fig. 2). Since, as in wall-plus-membrane preparations, SDSsoluble polymer was simultaneously synthesized, it seems possible that, at high tunicamycin concentrations, a greater proportion of this soluble fraction consisted of molecules sufficiently large to be co-precipitated with the cells by trichloroacetic acid. How excess tunicamycin could achieve this effect is not clear. The synthesis of peptidoglycan by etherized Neisseria gonorrhoeae has been described (Brown & Perkins, 1979). In those experiments the incorporation of radioactivity from UDP[ “CIGlcNAc into the trichloroacetic acid-precipitated fraction was inhibited by 26% by 1 pg of tunicamycin/ml. In the present work, incorporation into hot-SDS-soluble and -insoluble fractions was examined (Fig. 3). Concentrations of tunicamycin as low as 0.005pg/ml caused a 20% fall in the synthesis of the hotSDS-soluble fraction and an initial small rise in the synthesis of the SDS-insoluble (i.e. wall-bound) fraction. Further effects were not observed until a concentration of 10pg/ml was exceeded, when considerable inhibition of incorporation into both fractions took place. The low-concentration effect of favouring the synthesis of wall-bound material at the expense of the soluble fraction could, perhaps, represent a tendency for existing partially cross-linked chains to be extended, rather than new chains to be initiated, in the presence of the drug. Alternatively, the limited effect may imply a separate population of polymer made at highly tunicamycin-sensitive synthetic centres. In Bacillus licheniformis preparations, Ward (1 977) also observed an increase in synthesis of wall-bound peptidoglycan at low concentrations of tunicamycin.