Understanding biofilm formation on aircraft materials Martin Warburton 1 , Jaime Gomez-Bolivar 2 , Juan F. Mujica-Alarcón 2 , James Barnes 3 , Myrsini Chronopoulou 4 , Steve Thornton 5 , Stephen A. Rolfe 2 , Jesús J. Ojeda 1 1 Swansea University, UK, 2 University of Sheffield, UK, 3 Airbus Operations Ltd, UK, 4 Conidia Bioscience Ltd, UK, 5 Department of Civil & Structural Engineering, University of Sheffield, UK Microbial contamination and biofilm formation on the surfaces of aircraft fuel tanks are major challenges in the aviation industry. The inevitable presence of water, together with the nutrients provided by the fuel compounds, make an ideal environment for some bacteria, fungi and yeast to grow. Understanding how microbes attach to different fuel tank materials is the first step to develop ways to avoid or minimise bacterial attachment to these surfaces. In this study, biofilms of Pseudomonas putida (a model Gram-negative bacterium previously found in aircraft fuel tanks) were characterised on P60A epoxy primer and aluminium alloys 7075-T6, 2024-T3 and anodized 2024-T3. A combination of spectroscopic and microscopic techniques (including confocal microscopy, SEM, micro-FTIR and XPS) were used to understand which macromolecules are important in attachment and chemical interactions between the bacteria and the surfaces at the water phase, fuel phase and water-fuel interface. Results using SEM-EDX showed that the extra-polymeric substances (EPS) produced by P. putida were important in biofilm-surface interactions. EDX analysis showed that the EPS was phosphorus-rich compared to bacterial cells. Additionally, different biofilm morphologies were observed in the water phase and the fuel phase. Analyses obtained using depth-profile XPS were in agreement with the results observed with SEM-EDX, where the amount of phosphorus increased closer to the aluminium surface. Micro-FTIR analysis suggested that phosphoryl and carboxyl functional groups play a fundamental role in the irreversible attachment between the EPS and the aluminium surface, by the formation of hydrogen bonds and inner-sphere complexes between the macromolecules and the metals. This study presents initial evidence of which biological macromolecules and main chemical functional groups are responsible of the attachment of a typical microorganism found in the fuel tanks of aircraft, as well as providing a mechanistic understanding of the interactions of these biomacromolecules at the biofilm-surface interface.
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