In situ microstructure and rheological behavior of yeast biofilms from the juice processing industries

Biofilm mechanics in an extremely acidic environment: microbiological significance

A variety of natural biofilms were collected from an extremely acidic environment at Río Tinto (Spain). In order to provide insights into the structure-function relationship, the microstructure of the biofilms was explored using low temperature scanning electron microscopy (LTSEM) in combination with rheological analysis. The creep-recovery experiment results have demonstrated the typical behaviour of viscoelastic materials that combine both elastic and viscous characters. The LTSEM visualization and rheological characterization of biofilms revealed that the network density increased in bacterial biofilms and was the lowest in protist Euglena biofilms. This means that, in the latter biofilms, a lower density of interactions exist, suggesting that the whole system experiences enhanced mobility under external mechanical stress. The samples with the highest dynamic moduli (Leptospirillum-Acidiphilium, Zygnemopsis, Chlorella and Cyanidium) have shown the typical strain thinning behaviour, whereas the Pinnularia and Euglena biofilms exhibited a viscous thickening reaction. The Zygnemopsis filamentous floating structure has the highest cohesive energy and has shown distinctive enhanced resilience and connectivity. This suggests that biofilms should be viewed as soft viscoelastic systems the properties of which are determined by the main organisms and their extracellular polymeric substances. The fractional Maxwell model has been found to explain the rheological behaviour of the observed complex quite well, particularly the power-law behaviour and the characteristic broad relaxation response of these systems.

The mechanical properties of microbial surfaces and biofilms

Microbes can modify their surface structure as an adaptive mechanism for survival and dissemination in the environment or inside the host. Altering their ability to respond to mechanical stimuli is part of this adaptive process. Since the 1990s, powerful micromanipulation tools have been developed that allow mechanical studies of microbial cell surfaces, exploring little known aspects of their dynamic behavior. This review concentrates on the study of mechanical and rheological properties of bacteria and fungi, focusing on their cell surface dynamics and biofilm formation.

Biofilms in Food Processing Environments: Challenges and Opportunities

This review examines the impact of microbial communities colonizing food processing environments in the form of biofilms on food safety and food quality. The focus is both on biofilms formed by pathogenic and spoilage microorganisms and on those formed by harmless or beneficial microbes, which are of particular relevance in the processing of fermented foods. Information is presented on intraspecies variability in biofilm formation, interspecies relationships of cooperativism or competition within biofilms, the factors influencing biofilm ecology and architecture, and how these factors may influence removal. The effect on the biofilm formation ability of particular food components and different environmental conditions that commonly prevail during food processing is discussed. Available tools for the in situ monitoring and characterization of wild microbial biofilms in food processing facilities are explored. Finally, research on novel agents or strategies for the control of biofilm formation or removal is summarized.