Influence of carbon source complexity on porosity, water retention and extracellular matrix composition of Neurospora discreta biofilms

Aims To evaluate carbon source complexity as a process lever to impact the microstructure, chemical composition and water retention capacity of biofilms produced by Neurospora discreta. Methods and Results Biofilms were produced by nonpathogenic fungus N. discreta, using sucrose, cellulose or lignin as carbon source. The increase in complexity of carbon source from sucrose to lignin resulted in decreased water retention values (WRV) and wet weights of harvested biofilms. Confocal laser scanning microscopy was used to calculate porosity from bright-field images, and relative stained areas of cells and carbohydrates from fluorescence imaging of samples stained with Trypan blue and Alexa Fluor 488. Porosity and relative quantity of cells increased with increase in carbon source complexity while the amount of carbohydrates decreased. The chemical analysis of the extracted extracellular matrix (ECM) showed that biofilms grown on more complex carbon sources had lower carbohydrate and protein content, which also explains the lower WRV trend, as carbohydrates are hydrophilic. Conclusions The nature of carbon source impacts the metabolic pathway of cells, thereby influencing the relative proportions of ECM and cells. This in turn impacts the microstructure, composition and water content of biofilms. Significance and Impact of the Study This work shows that carbon source can be used as process lever to control the properties of biofilms and presents a novel view of biofilms as potentially useful biomaterials.