In vitro assessment of inter-kingdom biofilm formation by bacteria and filamentous fungi isolated from a drinking water distribution system

The main focus so far in the study of biofilm formation in drinking water has been bacteria. Studies on biofilm formation involving filamentous fungi are, therefore, scarce. This study aimed to assess and characterize the ability of these microorganisms to interact with bacteria whilst forming inter-kingdom biofilms. Biofilms were analysed in terms of total biomass, metabolic activity, bacterial colony forming units and morphology by epifluorescence microscopy. The quantitative methods revealed that biofilm mass increased over time for both single and inter-kingdom biofilms, while specific metabolic activity decreased, in general, along the time points evaluated. Microscopic data visually confirmed the biofilm mass increase over time. This study shows that fungal stage development is important in the first 24?h of biofilm formation. Inter-kingdom biofilm formation is microorganism dependent and inter-kingdom biofilms may provide an advantage to the opportunistic bacterium Acinetobacter calcoaceticus to replicate and proliferate when compared with Methylobacterium oryzae.Tiago B. Afonso acknowledges the grant provided by the Portuguese Foundation for Science and Technology (FCT) under grant no. PD/BD/128033/2016. This study was also supported by FCT under the scope of the strategic funding of UID/BIO/04469/2019 unit and BioTecNorte operation (NORTE-01-0145-FEDER-000004) funded by the European Regional Development Fund under the scope of Norte2020 – Programa Operacional Regional do Norte. Fundação para a Ciência e a Tecnologia.