Marra, Daniele (2025) Role of gravity and shear stress on bacterial motility and biofilm morphology. [Tesi di dottorato]

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Abstract

Biofilm proliferation in confined environments poses significant challenges across various fields, from contamination of biomedical devices to fouling of industrial equipment. Evidence of biofilm growth has also been documented beyond Earth, aboard the International Space Station (ISS), under unique microgravity conditions. A notable example, of biofilms negative implication on ISS, is the Water Recovery System (WRS), where surfaces in contact with flowing liquids have experienced biofilm-related fouling, leading to functional failures. Microgravity introduces additional challenges, with contradictory studies reporting altered bacterial growth, gene expression, and biofilm morphology. These findings remain inconclusive, with contrasting behaviours observed between motile and non-motile bacterial strains, suggesting an intricate interplay between gravity and motility in shaping biofilms. This doctoral thesis systematically investigates the combined effects of shear stresses and gravity vector on bacterial motility and biofilm formation. A microfluidic approach, combined with advanced image analysis techniques, was employed to characterize bacterial trajectories and biofilm development in confined environments under controlled laminar flow. Results reveal a measurable impact of gravity on bacterial spatial organization, motility, and biofilm morphology. Additionally, space-relevant variables such as nanoparticle coatings and Relative Humidity control were investigated to develop strategies for controlling microbial adhesion and facilitating biofilm removal from surfaces. To deepen the understanding between motility and biofilm, the CRISPR/Cas9 interference was implemented to silence flagellar genes in two bacterial strains: Pseudomonas fluorescens and Bacillus subtilis. This research not only advances our understanding of biofilm development under mechanical stresses but also lays the groundwork for designing sustainable solutions to support long-term space exploration.

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