The Role of Isocitrate Lyase (ICL1) in the Metabolic Adaptation of Biofilms.

Background: A major characteristic of biofilm cells that differentiates them from free-floating cells is their high tolerance to antifungal drugs. This high resistance is attributed to particular biofilm properties, including the accumulation of extrapolymeric substances, morphogenetic switching, and metabolic flexibility.

Objectives: This study evaluated the roles of metabolic processes (in particular the glyoxylate cycle) on biofilm formation, antifungal drug resistance, morphology, and cell wall components.

Methods: Growth, adhesion, biofilm formation, and cell wall carbohydrate composition were quantified for isogenic ICL1/ICL1, ICL1/, and / strains. The morphology and topography of these strains were compared by light microscopy and scanning electron microscopy. (glucan synthase), (14-α-demethylase), and (efflux pump) mRNA levels were quantified using qRT-PCR.

Results: The ICL1/icl1 and / strains formed similar biofilms and exhibited analogous drug-tolerance levels to the control ICL1/ICL1 strains. Furthermore, the drug sequestration ability of β-1, 3-glucan, a major carbohydrate component of the extracellular matrix, was not impaired. However, the inactivation of ICL1 did impair morphogenesis. ICL1 deletion also had a considerable effect on the expression of the , , and genes. and were upregulated in ICL1/ and / cells throughout the biofilm developmental stages, and was upregulated at the early phase. However, their expression was downregulated compared to the control ICL1/ICL1 strain.

Conclusions: We conclude that the glyoxylate cycle is not a specific determinant of biofilm drug resistance.