FIGURE 3: Environmental cues determine cell fate. All three differentiation fates occur as nutrients become depleted, and this depletion provides at least three environmental cues that control differentiation fate as follows.

(i) The ratio of non-fermentable carbon sources to fermentable carbon sources (NFCs/FCs) affects fate, with higher levels of NFCs stimulating sporulation (Sp). The arrow + bar shown linking NFCs/FCs to pseudohyphal growth (phg) reflects that in some laboratory strain backgrounds phg occurs efficiently when a FC source (glucose), is present, whereas in other strain backgrounds this differentiation occurs more efficiently in a NFC (acetate).

(ii) Alkali increases in the environment during late stages of growth, and this alkali promotes both quiescence (Q) and sporulation.

(iii) Nitrogen and possibly other essential nutrients (N) inhibit both, sporulation and quiescence. The arrow bar connecting N to phg represents that phg occurs most efficiently when intermediate levels of N are present, i.e. Phg is inefficient at either high N or in the absence of N.