Pichia fermentans dimorphic changes depend on the nitrogen source

Pichia fermentans DiSAABA 726 is a biofilm-forming yeast that undergoes dimorphic transition.
Under yeast-like morphology it controls brown rot caused by Monilia spp. on apple
fruit, while under pseudohyphal form, it shows pathogenic behaviour itself on peach fruit.
The present study investigates the nutritional factors that induce and separate yeast-like
and pseudohyphal morphologies under laboratory conditions. We show that P. fermentans
DiSAABA 726 produces mainly yeast-like cells on media containing millimolar concentrations
of urea and diammonium phosphate, and forms pseudohyphae at micromolar concentrations
of these two salts. With ammonium sulphate, yeast-like or pseudohyphal
morphology depends on the N concentration and the pH of the culture media. Amino acids
such as methionine, valine, and phenylalanine invariably induce pseudohyphal morphology
irrespective of the N concentration and the pH of the culture media. Methionol,
1-butanol, isobutanol, and isopropanol induce pseudohyphal growth, while phenylethanol
and isoamyl alcohol fail to induce the formation of filaments. Thus, the morphogenesis of
P. fermentans DiSAABA 726 depends more on the nitrogen source than on the N concentration,
and is regulated by the quorum-sensing molecules that are generally produced from
amino-acid assimilation under nitrogen starvation.