Quorum Sensing-Mediated, Cell Density-Dependent Regulation of Growth and Virulence in Cryptococcus neoformans

Abstract

ABSTRACT Quorum sensing (QS) is a cell density-dependent mechanism of communication between microorganisms, characterized by the release of signaling molecules that affect microbial metabolism and gene expression in a synchronized way. In this study, we investigated cell density-dependent behaviors mediated by conditioned medium (CM) in the pathogenic encapsulated fungus Cryptococcus neoformans . CM produced dose-dependent increases in the growth of planktonic and biofilm cells, glucuronoxylomannan release, and melanin synthesis, important virulence attributes of this organism. Mass spectrometry revealed the presence of pantothenic acid (PA) in our samples, and commercial PA was able to increase growth and melanization, although not to the same extent as CM. Additionally, we found four mutants that were either unable to produce active CM or failed to respond with increased growth in the presence of wild-type CM, providing genetic evidence for the existence of intercellular communication in C. neoformans . C. neoformans CM also increased the growth of Cryptococcus albidus , Candida albicans , and Saccharomyces cerevisiae . Conversely, CM from Cryptococcus albidus , C. albicans , S. cerevisiae, and Sporothrix schenckii increased C. neoformans growth. In summary, we report the existence of a new QS system regulating the growth and virulence factor expression of C. neoformans in vitro and, possibly, also able to regulate growth in other fungi. IMPORTANCE Quorum sensing is a strategy of communication used by pathogenic microorganisms to coordinate the expression of attributes necessary to cause disease. In this work, we describe a quorum sensing system in Cryptococcus neoformans , a yeast that can cause severe central nervous system infections. Adding conditioned medium—culture medium in which C. neoformans has previously grown—to fresh cultures resulted in faster growth of C. neoformans both as isolated cells and in microbial communities called biofilms. The addition of conditioned medium also increased the secretion of capsule carbohydrates and the formation of melanin pigment, two tools used by this microorganism to thrive in the host. This remarkable example of microbial communication shows that C. neoformans cells can act in unison when expressing attributes necessary to survive in the host, a finding that could point the way to improvements in the treatment of cryptococcosis.