BICARBONATE-MEDIATED SOCIAL COMMUNICATION STIMULATES MEIOSIS AND SPORULATION OF SACCHAROMYCES-CEREVISIAE

Meiosis and sporulation in the yeast Saccharomyces cerevisiae requires social communication, mediated by an extracellular factor which is se creted from cells during sporulation and accumulates in a cell density -dependent manner. We show here genetic and biochemical analyses suppo rting our conclusion that the extracellular factor is bicarbonate acti ng as an alkali to elevate extracellular pH. Sporulation defects of md h1 (mitochondrial malate dehydrogenase) mutants and of wild-type cells at low density were rescued extracellularly by addition of bicarbonat e or other alkaline solutions to raise medium pH. Addition of bicarbon ate (or alkalization of medium) raised steady-state levels of mRNA in respiration-deficient mdh1 mutants and inhibited proliferation of wild -type cells at low density. These results indicate that the two condit ions (respiration competency and high cell density), required for meio sis and sporulation, are essential for extracellular accumulation of b icarbonate and resulting alkalization of medium. (C) 1998 John Wiley & Sons, Ltd.