Biofilm formation by zygomycetes: quantification, structure and matrix composition.

Area of Science:

• Mycology
• Microbiology
• Biomedical Sciences

Background:

• Fungal biofilms are crucial in persistent infections, with most research focusing on Candida and Aspergillus.
• Biofilm formation in zygomycetes, a group of fungi with significant medical relevance, remains largely unexplored.
• Understanding zygomycete biofilm capacity is vital for developing targeted antifungal strategies.

Purpose of the Study:

• To investigate and report on the biofilm-forming capacity of four zygomycete species: Rhizopus oryzae, Lichtheimia corymbifera, Rhizomucor pusillus, and Apophysomyces elegans.
• To characterize the biofilm matrix composition of the studied zygomycetes.
• To determine if Apophysomyces elegans exhibits biofilm formation under tested conditions.

Main Methods:

• Standardized microtitre plate assays were used to evaluate biofilm formation at 37°C for 24 hours.
• Seeding spore densities were optimized for each species to assess adherence and structure formation.
• Phase-contrast and confocal microscopy were employed to visualize biofilm architecture and thickness.
• Biochemical analysis was performed to identify components of the extracellular matrix, including glucosamine, N-acetylglucosamine, glucose, and proteins.

Main Results:

• Rhizopus oryzae, Lichtheimia corymbifera, and Rhizomucor pusillus successfully formed robust, adherent biofilms characterized by intertwined hyphae encased in an extracellular matrix.
• Biofilm thickness varied among the species, with Lichtheimia corymbifera forming the thickest biofilms (242±23.07 µm).
• The extracellular matrix primarily consisted of glucosamine (74.54-82.22% dry weight), N-acetylglucosamine, glucose, and proteins.
• Apophysomyces elegans did not exhibit significant adherence or biofilm formation, even with varied seeding densities.

Conclusions:

• This study provides the first evidence of significant biofilm formation in Rhizopus oryzae, Lichtheimia corymbifera, and Rhizomucor pusillus.
• The findings underscore the potential for these medically important zygomycetes to form biofilms, posing a challenge in clinical settings.
• Apophysomyces elegans appears to lack the capacity for biofilm formation under the conditions tested, suggesting species-specific variations within zygomycetes.