Fig. 6.

Survival of NZ131 and OK171 in buffered medium. The strains were grown in THY medium buffered with 10 mM HEPES buffer, pH 7.4. After the first week of incubation, the pH of both cultures stabilized at pH ~6.5 and remained at this value for the remainder of the experiment. Similarly, both populations stabilized at ~10⁵ cells ml⁻¹, a drop of about 1000-fold from the maximum cell density. The experiment was discontinued after 70 days. The lines show the c.f.u. values for the cultures, and the areas filled with vertical and horizontal lines indicate the pH (NZ131 and OK171, respectively).