Calling a Microscopic Quorum: How Fungi Communicate

C. neoformans as single cells. Image credit: Gross L (2006) Iron Regulation and an Opportunistic AIDS-Related Fungal Infection. PLoS Biol 4(12): e427. doi:10.1371/journal.pbio.0040427.


Microbes find strength in numbers. Rarely alone, they live in communities and share resources by coordinating their biological processes. Just as governing bodies require a quorum, or a minimum number of people present, before deciding something on behalf of the entire group, many species of microbes must establish a quorum before coordinating their behavior. Microbes do this through quorum sensing, in which they release signaling molecules such as hormones or small proteins into the surrounding area and then sense the concentration of those signals. As more microbes enter the environment, the concentration of the signaling molecule will increase. Once the microbes sense that the concentration has met a certain threshold, they will initiate a particular biological process.


Microbes often use quorum sensing to determine when to release virulence factors, molecules that will help them overwhelm their target and establish an infection. They only want to spend energy making a virulence factor when there are other cells present because if too few microbes are present, they will not make enough virulence factors to successfully infect their target, and thus will have wasted energy. Quorum sensing systems have been very well characterized in bacteria but not as well in other microbes. In a recent study in the journal Cell Host & Microbe, Homer and colleagues identified and characterized a quorum sensing system in a eukaryotic microbe, the pathogenic fungus Cryptococcus neoformans, which is the most common cause of fungal meningitis [1]. They found that fungal cells with a mutation in the quorum sensing signaling molecule gene, qsp1, were less successful at infecting mice than C. neoformans cells with a fully functional quorum sensing signaling molecule. Through a series of experiments, they elucidated other components of the quorum sensing pathway and found that qsp1 functions inside the fungal cell to control virulence. Previous work identified a quorum sensing system in the pathogenic fungus Candida albicans, but the quorum sensing molecule discovered is produced by many different organisms [2]. Because the newly discovered quorum sensing system described here is specific to C. neoformans, it presents the unique opportunity to develop strategies to specifically disrupt the ability of C. neoformans to cause disease.


-Stephanie DeMarco (@sci_steph)
Staff Writer, Signal to Noise Magazine
PhD Candidate, Molecular Biology

References:

[1] Homer CM, Summers DK, Goranov AI, Clarke SC, Wiesner DL, Diedrich JK, Moresco JJ, Toffaletti D, Upadhya R, Caradonna I, Petnic S, Pessino V, Cuomo CA, Lodge JK, Perfect J, Yates JR 3rd, Nielsen K, Craik CS, Madhani HD. Intracellular Action of a Secreted Peptide Required for Fungal Virulence. Cell Host & Microbe. (2016). DOI: 10.1016/j.chom.2016.05.001.

[2] May RC. Custom-Made Quorum Sensing for a Eukaryote. Developmental Cell. (2016). DOI: 10.1016/j.devcel.2016.05.014.