Farnesol

In the opportunistic pathogen Candida albicans , hyphal growth and virulence factor expression are regulated by environmental and chemical cues. Farnesol is a secreted autoregulatory molecule that represses filamentation. It is derived from farnesyl pyrophosphate (FPP), an ergosterol biosynthesis pathway intermediate. Although Dpp1, Dpp2, and Dpp3 were proposed to synthesize farnesol, a mutant lacking all three had only a modest reduction in farnesol. To identify other farnesol biosynthesis genes, we employed transcription factor mutants that underproduced or overproduced farnesol in a screen and analyzed their transcriptomes. CWH8 was the only transcript correlated with farnesol production. Cwh8 is a lipid phosphatase known to recycle dolichyl pyrophosphate during glycosylation of cell wall proteins. The cwh8ΔΔ mutant had a > 99% reduction in farnesol compared to the parent strain and was hyperfilamentous in embedded conditions. It had ~900 fold lower levels of farnesyl phosphate, the product of FPP dephosphorylation, suggesting Cwh8 acts directly on FPP. Complementation of the C. albicans cwh8ΔΔ mutant with CWH8 from C. albicans restored cell wall integrity and farnesol production. However, complementation with CWH8 from Clavispora lusitaniae , a species lacking farnesol signaling, restored cell wall integrity but failed to rescue farnesol production. This indicates that while Cwh8’s role in maintaining cell wall integrity is conserved, differences in substrate specificity or interactions with species-specific cofactors underlie its involvement in farnesol biosynthesis in C. albicans . Finally, fluconazole was fungicidal for cwh8ΔΔ rather than fungistatic. These studies demonstrate how an extracellular signaling system can arise and be co-opted to promote fungal fitness in complex environments.

Farnesol secretion distinguishes the human opportunistic pathogen Candida albicans from non-secreting, non-pathogenic yeasts. Despite 20 years of research, surprisingly little is known about how farnesol is synthesized and regulated. Using transcriptomic profiles from mutants with altered farnesol production, we identified CWH8 as a critical enzyme in this process. CWH8 null mutants produced no farnesol. Our novel assay measuring cellular farnesyl pyrophosphate (FPP) and farnesyl phosphate (FP) showed that Cwh8 converts FPP to FP in the first step of farnesol biosynthesis, in addition to its established role in recycling dolichyl pyrophosphate. Farnesol-secreting fungi had huge metabolic pools of FP, while nonsecretors had small pools. Furthermore, expressing CWH8 from Clavispora lusitaniae , a non-farnesol-secreting species, failed to restore farnesol production in C. albicans . This suggests that changes in Cwh8 enzyme specificity drove the evolution of farnesol as a signaling molecule and virulence factor in C. albicans .

This study conducted a nontargeted screening of food contact paper products, including samples with seven usage types and made from six distinct materials. By using an optimized headspace SPME GC-QTOF MS method, 277 volatiles were identified in 70 samples. Chemometric analysis revealed significant variations among the samples. A total of 30 main odorants and 18 odor contributors, including substances with positive or negative odors, were identified. A risk scoring scheme was developed to identify 33 high-risk substances rapidly, and the distribution characteristics of these substances in different samples were further studied. The potential origins of the main odorants and high-risk substances were traced to raw materials and intentionally or unintentionally added substances. Correlation analysis indicated that several high-risk substances with highly significant correlations coexisted in the samples. Overall, this study provides valuable insights for the food contact paper industry and supports efforts to enhance food safety and consumer health protection.