AMMONIA MEDIATES COMMUNICATION BETWEEN YEAST COLONIES

Under certain growth conditions unicellular organisms behave as highly organized multicellular structures. For example, the fruiting bodies of myxobacteria(1) and of the slime mould Dictyostelium discoideum(2) form structures composed of non-dividing motile cells. Although non-mo tile, yeasts can create organized structures, colonies in which cells communicate and act in a coordinated fashion. Colony morphologies are characteristic for different species and strains. Here we describe tha t, in addition to short-range intracolony cell-cell communication, yea sts exhibit long-distance signals between neighbouring colonies. The v olatile alkaline compound ammonia, transmitted by yeast colonies in pu lses, has been identified as a substance mediating the intercolony sig nal. The first alkaline pulse produced by neighbouring colonies is non -directed and is followed by acidification of the medium. The second p ulse seems to be enhanced and is oriented towards the neighbour colony . Ammonia signalling results in growth inhibition of the facing parts of both colonies. This phenomenon is observed in different yeast gener a. The presence of amino acids in the medium is required for ammonia p roduction, Colonies derived from the yeast Saccharomyces cerevisiae sh r3 mutant, defective in localization of amino-acid permeases(3), do no t produce detectable amounts of ammonia and do not exhibit asymmetric growth inhibition.