A C. albicans two component pathway regulates the CDR4 and SSU1 transport genes involved in quorum sensing and response to bacterial signaling molecules.

• Main Authors: Stuffle, Derek A, Kruppa, Michael D, Dr.
• Format: Others
• Published: Digital Commons @ East Tennessee State University 2018
• Subjects: Candida albicans; quorum sensing; biofilms; two-component signaling; Pathogenic Microbiology
• Online Access: https://dc.etsu.edu/asrf/2018/schedule/109

Polymicrobial communities of bacterial and fungal species are present on the skin and mucosal surfaces of the body. Invasive infections caused by Candida species are commonly seen in immunocompromised individuals (HIV, transplants, cancer) and ranks as the third leading cause of infection in hospitalized patients. C. albicans is a polymorphic opportunistic fungus that infects critically ill patients and has the ability to change its morphology from yeast to hyphal form.The morphogenesis of C. albicans is a major aspect of its virulence and is regulated by quorum sensing (QS) molecules they produce, as well as the presence of neighboring microbes.In this study, we examined two transporter mutants, cdr4 and ssu1, for their ability to form biofilms in the presence of cyclic-di-GMP and 3-oxo-12-homoserine lactone. To quantify biomass, wild type and mutant cells were grown overnight at 30˚C in YPD. The cells were washed, counted and diluted to a desired density of 106 cells/ml in medium 199, pH7.5. Cells were added to 96-well plates pre-incubated with 5% fetal bovine serum at densities of 105, 104, and 103 cells/well and allowed to adhere at 37˚C for one hour. The wells were then covered with fresh M199 media containing the QS molecule and monitored for 48 hours at 37˚C. After this time, the media and planktonic cells were removed. The biofilms were fixed with methanol, dried, then stained with 0.05% crystal violet. Bulk biomass was assessed by spectrophotometry. We did observe a difference in biofilm density when incubated in the presence of cyclic-diGMP. We noted that for the wild type and ssu1 strain their biofilms biomass increased by as much as 10% at 104 and 103 cell densities when compared with the control. While the cdr4 strain had a slight reduction in biofilm density when cyclic-diGMP was present. This result also indicates a potentially positive role in which cyclic-diGMP can help C. albicans develop denser biofilms, potentially in the presence of bacteria like P. aeruginsa, which secrete cyclic di-GMP, but kill hyphal forms of C. albicans. Additionally, it has been shown that C. albicans mutants lacking the hybrid histidine kinase, Chk1p, are refractory to the effects of farnesol, a QS molecule that inhibits morphogenesis.Given that mutations in CDR4 and SSU1 impact the QS response in C. albicans, we investigated whether these genes were regulated through two-component signaling by Chk1. To assess CDR4 and SSU1 expression, wild type and mutant strains were grown overnight in YPD media at 30˚C. Cells were then harvested and RNA was obtained by acid phenol extraction. Using RT-PCR, we determined both CDR4 and SSU1 expression is reduced or highly repressed in the chk1, ypd1, and skn7 null strains. These results suggest the two genes are downstream targets in a pathway regulated by Chk1p. The finding that QS proceeds through a two-component pathway can be exploited in antifungal drug development. Given that two-component signaling is absent in mammalian cells, development of novel compounds that interfere with this pathway may be a useful alternative for treating patients with candidiasis.