The Role of Inter-Kingdom Interactions by Drinking Water-Isolated Microorganisms in Biofilm Development and Control

Bacteria and filamentous fungi (ff) are commonly encountered in biofilms developed in drinking water (DW) distribution systems (DWDS). Despite their intimate ecological relationships, researchers tend to study bacteria and ff in splendid isolation. This work assesses the impact of bacteria-ff association in biofilm formation and tolerance to sodium hypochlorite (SHC). One strain of Acinetobacter calcoaceticus isolated from DW was used as a model bacterium. Penicillium brevicompactum and P. expansum isolated from DW were the ff selected. Single species and inter-kingdom adhesion and biofilm formation occurred in 96-wells polystyrene microtiter plates under two shear stress (τ) conditions (0.05 and 1.6 Pa). The sessile structures were further characterized by colorimetry and fluorescence-based methods, for biomass and metabolic activity assessment. A. calcoaceticus cells in biofilms were further quantified in terms of colony forming units. The results showed that 1.6 Pa of shear stress and A. calcoaceticus-ff association favoured biofilm production. Inter-kingdom biofilms produced more biomass than the A. calcoaceticus single species. These biofilms further reduced A. calcoaceticus susceptibility to disinfection. In addition, Penicillium brevicompactum formed single biofilms highly resistant to removal and inactivation by SHC. The presence of P. brevicompactum or P. expansum in inter-kingdom biofilms significantly decreased SHC removal and inactivation effects in comparison to the bacterial biofilms alone, proposing that using bacteria to form biofilms representative of DWDS can provide inaccurate conclusions, particularly in terms of susceptibility to disinfection