Spaceflight-Induced Changes in Polymicrobial Biofilm Structure and Silver Susceptibility

Abstract

Biofilms, surface-adherent microbial populations, represent a common mode of bacterial growth in nature and in built environments, including the water recovery system (WRS) in spacecraft. Several factors have been associated with biofilm structure, including shear forces associated with turbulent flow, microbial community composition, and available nutrients and other culture conditions. Here we investigated biofilm formation of a mixed Escherichia coli F11-mCherry - Pseudomonas aeruginosa PAO1-gfp culture during microgravity in spaceflight, and full gravity (ground control), in BioCellTM flight hardware with an artificial urine medium. At the early 4-d time point in spaceflight samples, the gas-permeable Teflon membrane on the BioCell hardware surface was heavily colonized by green-fluorescing P. aeruginosa, whereas the underlying 316L stainless steel coupon had a notable red-fluorescing E. coli population. The 4-d spaceflight P. aeruginosa Teflon biofilm had a clumped appearance with regions of higher cell density (microcolonies) and low cell density (water channels). Interestingly, the overall structure resembles Van Gogh’s Starry Night. In contrast, the corresponding 4-d ground control P. aeruginosa-dominated Teflon biofilm was completely uniform with no obvious clumping. At later time points (14-d and 117-d), P. aeruginosa became much more prominent on both Teflon and stainless steel surfaces, the unique spaceflight biofilm structures were no longer observed and the overall populations decreased. Based on our results and similar findings of other investigators, we propose that microgravity conditions during spaceflight represent a factor that can influence biofilm structure in some culture conditions.Biolog