Table 1.
List of strains used in this study.
Fig 1.
Overview of PGBs used as model in this study.
a | Macro image of a PGB showing side (left) and top views (right). b | SEM image of the flat bottom area of a PGB. c | SEM image of a PGB. d | Macro image of the Sahara sand used for FT-Raman. e | SEM image of Sahara sand (arrow) alongside a PGB particle. f | NIR FT-Raman spectra of PGB (1) and Sahara sand (3) compared to a reference fused silica (amorphous quartz glass, 2) and rose quartz (crystalline quartz, 4). The Raman intensities of all spectra shown were min-max normalized and vertically shifted for better visualization.
Fig 2.
Biofilm formation of all strains on PGBs 24 hours post-inoculation, visualized by CLSM.
Images show the entire flat-bottom area of the PGB measuring 4 mm in diameter. Bacteria are stained with DAPI (cyan). All strains exhibit strong biofilm formation with bacterial aggregates predominantly localized at the rim of the PGBs.
Fig 3.
Biofilm formation of all strains on PGBs 72 hours post-inoculation, visualized by CLSM.
Images show the entire flat-bottom area of the PGB measuring 4 mm in diameter. Bacteria are stained with DAPI (cyan). At this time point, differences in biofilm formation between B. anthracis (a–e) and Bcbva strains (f–j) were evident. Bcbva strains displayed an overall reduced signal with a patchy distribution.
Fig 4.
Biofilm formation of all strains on PGBs 168 hours post-inoculation, visualized by CLSM.
Images show the entire flat-bottom area of the PGB measuring 4 mm in diameter. Bacteria are stained with DAPI (cyan). For B. anthracis strains (a-e), bacteria remained concentrated at the rim of the PGBs, though signal intensity decreased compared to earlier time points. This further decrease in signal was also observed for the Bcbva strains, which maintained their patchy distribution between the PGB particles.
Fig 5.
Quantitative analysis of cell and spore count of all tested B. anthracis and Bcbva strains.
Cell and spore counts (CFU and qPCR) of all Bcbva (a) and B. anthracis strains except VAR28A88 (b), which was excluded due to negligible CFU growth, making comparison unreliable. c | Spore ratio comparison between B. anthracis and Bcbva. B. anthracis VAR28A88, Bcbva CI, and Bcbva CAR-H were excluded due to their differing sporulation behavior. Significance was tested by Wilcoxon rank-sum test with Bonferroni correction. p-values are shown as: * = p < 0.05, ** = p < 0.01, *** = p < 0.001, **** = p < 0.0001.
Table 2.
Comparison of biofilm growth on PGBs between B. anthracis and Bcbva over 168 hours.
Fig 6.
Biofilm formation of four selected strains on PGBs 24 hours post-inoculation, visualized by SEM.
SEM images of B. anthracis Dobichau (a-c) and VAR28A88 (d-f) as well as Bcbva CI (g-i) and CA (j-l) with stepwise increasing magnification from left to right at the marked areas.
Fig 7.
Biofilm formation of four selected strains on PGBs 72 hours post-inoculation, visualized by SEM.
SEM images of B. anthracis Dobichau (a-c) and VAR28A88 (d-f) as well as Bcbva CI (g-i) and CA (j-l) with stepwise increasing magnification from left to right at the marked areas. Spores are exemplary marked with white arrows.
Fig 8.
Biofilm formation of four selected strains on PGBs 168 hours post-inoculation, visualized by SEM.
SEM images of B. anthracis Dobichau (a-c) and VAR28A88 (d-f) as well as Bcbva CI (g-i) and CA (j-l) with stepwise increasing magnification from left to right at the marked areas. Spores are exemplary marked with white arrows.