Monday, 28 December 2015

Shape-shifting Candida albicans

Candida albicans on a Petri dish
A fungus found in the mucus of patients with cystic fibrosis - Candida albicans - has been examined by researchers. It has been discovered that the fungal species has evolved to defend itself against neighboring bacteria.

Candida albicans is a remarkable fungus. Its signature maneuver is shapeshifting -- it can morph from a round, single-celled yeast into a long stringy structure, allowing it to adapt to different environments and making it exceptionally harmful. In a recent study, researchers analyzed 89 mucus samples from 28 cystic fibrosis patients, using both high-throughput genetic sequencing as well as culture-based analysis. Candida albicans was predictably prevalent.

What was surprising is that that some of the fungi began shifting into its stringy shape without any environmental cue -- usually this transformation (filamentation) does not happen spontaneously, but is triggered by the presence of certain substances, such as blood. To see if there could be a genetic explanation, the researchers sequenced the genomes of these samples and found a common denominator. All but one had genetic mutations in a gene known to repress the change shape -- called NRG1.

To find out why certain strains of this fungus would have developed this genetic variation, researchers looked to neighbouring bacteria. As part of an ongoing battle between microbes, certain bacteria, which are also found in cystic fibrosis patients, secrete molecules preventing the fungus from changing into its stringy shape. The researchers tried exposing the mutated fungus to these bacterial rivals. Instead of responding to the bacterial signals, the fungus kept to its stringy form. The researchers believe these fungi have evolved to counter the tactics of their bacterial rivals.

For further details see:

Sang Hu Kim, Shawn T. Clark, Anuradha Surendra, Julia K. Copeland, Pauline W. Wang, Ron Ammar, Cathy Collins, D. Elizabeth Tullis, Corey Nislow, David M. Hwang, David S. Guttman, Leah E. Cowen. Global Analysis of the Fungal Microbiome in Cystic Fibrosis Patients Reveals Loss of Function of the Transcriptional Repressor Nrg1 as a Mechanism of Pathogen Adaptation. PLOS Pathogens, 2015; 11 (11): e1005308 DOI: 10.1371/journal.ppat.1005308

Posted by Dr. Tim Sandle