Candida albicans Biofilm Stiffness Is Controlled by Cell Wall Structure and Matrix Output

Fungal infections caused by Candida albicans are notoriously difficult to treat, and the biofilm the organism builds on catheters and implanted devices is a large part of the reason why. A study published in May 2026 in the journal Biofilm by Abriat, Huang, Sunder, and colleagues at the University of Michigan – Ann Arbor takes a fresh angle on the problem: measuring the physical stiffness and flow properties of those biofilms and tracing those properties to specific genes governing cell wall construction and matrix secretion.

Elastic Moduli of Wild-Type C. albicans Biofilms

The headline numbers are striking. Wild-type C. albicans biofilms grown for 14 days showed an elastic (storage) modulus of 18,400 ± 1,100 Pa and a viscous (loss) modulus of 1,700 ± 140 Pa, remaining nearly constant across frequencies from 0.1 to 10 s⁻¹. That ratio tells you the biofilm behaves far more like a solid than a liquid under ordinary shear. The yield stress, the force per unit area needed to make the material flow, came in at roughly 850 ± 60 Pa. Beyond that threshold, the biofilm relaxes with a characteristic time of 810 ± 19 seconds and an effective viscosity of 8.4 ± 0.2 MPa·s. In practical terms, a biofilm that stiff and that slow to relax will resist both mechanical removal during catheter care and the diffusion of antifungal drugs into its interior.

To generate these numbers reliably, the team developed a small-amplitude oscillatory rheology protocol specifically adapted for C. albicans. Growing the biofilm takes much longer than bacterial counterparts require, so the group designed an in vitro protocol calibrated to the organism's slow growth rate. Critically, they confirmed that the measurements were insensitive to gap distance, evaporative sealant choice, experiment duration, and specimen radius, a methodological rigor that has been missing from earlier biofilm mechanical property studies. Multiscale imaging, combining stereoscopic and confocal microscopy with SYTO 9 (cells, green) and Calcofluor White (chitin, blue) staining, revealed complex entanglement networks at the hundred-micrometer scale, showing that the mechanical behavior emerges from a genuinely three-dimensional, interwoven architecture.

Why Biofilm Stiffness Matters for Fungal Infections

The clinical consequences of C. albicans biofilm formation are severe. Biofilm-associated candidiasis carries high mortality, particularly in immunocompromised patients with indwelling devices, and existing antifungal drugs perform poorly against biofilm-embedded cells. A key reason is the extracellular matrix, a secreted tangle of polysaccharides, proteins, and lipids that sequesters antifungal drugs and shields cells from immune attack. Understanding the material properties of that matrix is therefore not an abstract exercise: a biofilm that is stiffer, more elastic, and slower to relax may be one that traps fluconazole more effectively or deforms less under shear flow in a catheter lumen.

The new data make this link explicit. Deletion mutants with disrupted matrix production, specifically strains lacking ALG11, KRE5, or PMR1, showed increased elastic moduli compared to wild type, meaning they were, counterintuitively, stiffer. Those same strains also displayed smooth biofilm morphology on agar, reduced hyphal content, decreased extracellular matrix, and reduced fluconazole resistance. The pairing of higher stiffness with lower drug resistance suggests that the stiffness measured here reflects a reorganized but less protective matrix, not a tougher one in a clinical sense.

How Chitin Synthase Mutations Reshape Biofilm Architecture

The composition of the C. albicans biofilm extracellular matrix is central to understanding these results. Chitin, a linear polysaccharide, makes up 1 to 15% of the fungal cell wall by mass, with the proportion varying between the yeast and hyphal growth forms. C. albicans is polymorphic: it can grow as ovoid yeast cells, elongated pseudohyphae, or true hyphae, and hyphae dominate structurally mature biofilms. Mutants with altered chitin synthase activity showed measurable differences in both phenotypic cell shape and rheological properties, confirming that the physical state of the biofilm is directly coupled to the cell-wall biosynthetic machinery.

Transcriptional profiling of the deletion mutants deepened the picture. The altered strains showed dysregulated expression across genes tied to cell membrane and cell wall biology, translation, protein catabolism, lipid metabolism, and filamentous development. The breadth of transcriptional change suggests that disrupting a single cell wall gene propagates through multiple regulatory networks, reshaping not just the matrix but the entire developmental program that governs whether cells elongate into hyphae.

Open Questions About Genetic Dissection of Biofilm Viscoelasticity

The study is explicit that a complete genetic dissection of rheological phenotypes is still ongoing. Three gene deletions, ALG11, KRE5, and PMR1, are entry points rather than a full map. Each modifies a distinct part of cell wall or membrane homeostasis: ALG11 participates in N-glycosylation, KRE5 in beta-1,3-glucan synthesis, and PMR1 in calcium and manganese transport that feeds into glycosylation pathways. Pulling on any one of these threads changes the biofilm's mechanical signature, but the field does not yet have a quantitative model that predicts how a given genetic perturbation will shift G', G'', or yield stress.

There are also practical experimental constraints. C. albicans biofilms require 14 days of culture before they are robust enough for rheometer tooling, compared with the hours or days needed for bacterial biofilms. That timeline makes high-throughput genetic screens slow and expensive. Novel strategies for tackling Candida biofilms will likely need to account for these long developmental timescales when designing drug or enzymatic disruption assays.

Targeting Cell Wall Genes to Disrupt Biofilm Mechanics

The study positions biofilm rheology as a distinct, quantifiable phenotype that can be used to evaluate mutants, benchmark new compounds, and eventually guide therapeutic strategy. The genes identified here, particularly those tied to ECM production and hyphal morphology, now become candidates for chemical inhibition or genetic intervention aimed at softening or destabilizing the biofilm matrix before antifungal treatment. If a drug can reduce the yield stress below the shear forces encountered in a vascular catheter, mechanical dislodgement becomes more feasible. If it reduces matrix density, fluconazole penetration improves.

Looking further ahead, the rheological framework developed here could integrate with research on polymicrobial Candida biofilms, where bacterial co-inhabitants alter both matrix composition and mechanical properties in ways that a single-species model cannot capture. That complexity is on the horizon; for now, having a reliable, validated method to measure fungal biofilm stiffness at all is itself a meaningful advance.