Reference strains improve reproducibility by standardizing observations and methodology, which has ultimately led to important insights in fungal pathogenesis. However, recent investigations have highlighted significant genotypic and phenotypic heterogeneity across isolates that influence genetic circuitry and virulence within a species. Candida glabrata is the second leading cause of candidiasis, a life-threatening infection, and undergoes extensive karyotype and phenotypic changes in response to stress. Much of the work conducted on this pathogen has focused on two sequenced strains, CBS138 (ATCC 2001) and BG2. Few studies have compared these strains in detail, but key differences include mating type and altered patterns of expression of EPA adhesins. In fact, most C. glabrata isolates and BG2 are MATa, while CBS138 is MATα. However, it is not known if other phenotypic differences between these strains play a role in our understanding of C. glabrata pathogenesis. Thus, we set out to characterize metabolic, cell wall, and host-interaction attributes for CBS138 and BG2. We found that BG2 utilized a broader range of nitrogen sources and had reduced cell wall size and carbohydrate exposure than CBS138, which we hypothesised results in differences in innate immune interactions and virulence. We observed that, although both strains were phagocytosed to a similar extent, BG2 replicated to higher numbers in macrophages and was more virulent during Galleria mellonella infection than CBS138 in a dose dependent manner. Interestingly, deletion of SNF3, a major nutrient sensor, did not affect virulence in G. mellonella for BG2, but significantly enhanced larval killing in the CBS138 background compared to the parent strain. Understanding these fundamental differences in metabolism and host interactions will allow more robust conclusions to be drawn in future studies of C. glabrata pathogenesis.
The authors are supported by the following funding sources - J.U.: BBSRC Discovery Fellowship (BB/W009625/1) and the MRC Centre for Medical Mycology [MR/N006364/2]. G.F.R.: PhD studentship from University of Aberdeen and the 466 Elphinstone Scholarship. D.S.C.: The Academy of Medical Sciences (SBF006\1128). We are grateful to our colleagues at the University of Aberdeen Institute of Medical Sciences core facilities and wish to acknowledge Andrea Holme and the Iain Fraser Cytometry Centre, and Debbie Wilkinson and Lucy Wight in the Microscopy and Histology Facility for training and assistance with cytometry and microscopy. We also thank Paulina Cherek and Dr Christian Hacker from the Bioimaging Centre at University of Exeter for the electron microscopy.
Data Availability StatementSupplementary material
Supplemental material is available online only
- Candida glabrata
- cell wall