Wayne R. Riekhof
Date of this Version
Wehling, C. (2020). DGTS Production as a Phosphate Starvation Response in the Human Fungal Pathogen Candida albicans.
Betaine lipids are a class of membrane lipids with betaine head groups. Three betaine lipids are known - diacylglyceryltrimethylhomoserine (DGTS), diacylglycerylhydroxymethylalanine (DGTA), and diacylglycerylcarboxymethylcholine (DGCC). Betaine lipids are most common in algae, although DGTS, the most common betaine lipid, is also found in many bacteria and fungi. Organisms which produce betaine lipids (especially DGTS) often don’t produce phosphatidylcholine (PtdCho), and DGTS structure resembles PtdCho structure without any phosphorous, leading to the hypothesis that betaine lipids may substitute for phospholipids in some organisms. This has been confirmed by discoveries that some organisms are capable of switching their membrane composition from PtdCho to DGTS in response to low environmental phosphate (Pi). Further work identifying the metabolic pathway of DGTS biosynthesis has demonstrated that DGTS biosynthesis is under control of Pi starvation response mechanisms (the PHO regulon) in bacteria and fungi. We therefore examined this response in the human fungal pathogen Candida albicans. Previous work in our lab showed that C. albicans encodes a DGTS biosynthesis (BTA1) ortholog (CaBTA1), and we here demonstrate that it is under control of the C. albicans PHO regulon and is thereby activated during Pi starvation. CRISPR/Cas9 deletion of BTA1 resulted in a lack of DGTS production and a significant decrease in overall growth in low-Pi conditions. Our work also suggests crosstalk between Pi starvation mechanisms, nitrogen sequestration, amino acid metabolism, and metal homeostasis. Our transcriptional data showed that BTA1 is induced in biofilm-promoting conditions regardless of Pi concentration. However, our results revealed no significant or consistent differences between wild type and bta1ΔΔ mutant biofilm formation or hyphal growth. Nevertheless, because C. albicans experiences Pi starvation in clinically relevant settings which can induce virulence (Romanowski et al., 2012) and because BTA1 deletion significantly impairs growth in low Pi conditions, DGTS production is likely an important tool for survival and infection in low Pi infection scenarios.
Advisor: Wayne R. Riekhof