Fig. 2: P. aeruginosa biofilm morphology on SS and LIS in 1 g or microgravity.

Representative confocal microscopy images of 1-, 2-, and 3-day-old biofilms formed over SS and LIS. Nucleic acids were stained with PI (red) and lipids were stained with Green Biofilm (green). First row per material is a bottom slice image with side-view panels of a cross-section point in the biofilm (specific section marked by the orange lines). Second row per material is a volume view of the complete z-stack image. Images correspond to biofilms grown in 1 g over a SS and b LIS, or for biofilms grown in microgravity over c SS and d LIS. Negative controls of the material surfaces, stained with both PI and Green Biofilm stains, are presented in panel (e). Scale bars are 20 µm. Biofilms form without boundaries on SS while on LIS they have sharp edges. Biofilms had significantly reduced surface area coverage on LIS, especially in microgravity where biofilms were minimized and mostly present as small groups of cells. The thin layer of nucleic acids on LIS surface could be DNA, RNA, or both as PI does not differentiate between them.