Avoiding microbial contamination and biofilm formation on the surfaces of aircraft’s fuel tanks is one of the 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 between the two immiscible phases (water-fuel interface). The mechanistic understanding of how microbes attach to different fuel tank materials is the first step in order to understand the procedures that need to be followed to avoid or minimise the bacterial attachment to these surfaces. In this study, the adhesion of Pseudomonas putida, a model Gram-negative bacterium previously found in fuel tanks of aircrafts, was characterised on different surfaces, including aluminium alloys 7075-T6, 2024-T3 and anodized 2024-T3, usually employed in aircraft’s fuel tanks due to their high strength and fatigue resistance. A combination of different spectroscopic and microscopic techniques (such as confocal microscopy, SEM, micro-FTIR and XPS) were used to understand which macromolecules are the main responsible of the initial attachment and chemical interactions between the bacteria and the surfaces at the water phase, fuel phase and water-fuel interface. Our results using SEM-EDX showed that the extra-polymeric substances (EPS) produced by P. putida were the main responsible of the biofilm-surface interactions. EDX analysis showed that the EPS were higher in phosphorus and nitrogen concentration than the whole bacterial cells. Additionally, different morphologies in biofilm formation were observed between 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 phosphorous increased when getting 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 initial and then irreversible attachment of a typical microorganism found in the fuel tanks of aircrafts, as well as providing a mechanistic understanding of the interactions of these biomacromolecues at the biofilm-surface interface.

Developing a mechanistic understanding of biofilm formation on aircraft materials

ACS Fall 2020 Virtual Meeting

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