Impact of Fe2+ and Shear Stress on the Development and Mesoscopic Structure of Biofilms—A Bacillus subtilis Case Study

Abstract

Bivalent cations are known to affect the structural and mechanical properties of biofilms. In order to reveal the impact of Fe2+ ions within the cultivation medium on biofilm development, structure and stability, Bacillus subtilis biofilms were cultivated in mini-fluidic flow cells. Two different Fe2+ inflow concentrations (0.25 and 2.5 mg/L, respectively) and wall shear stress levels (0.05 and 0.27 Pa, respectively) were tested. Mesoscopic biofilm structure was determined daily in situ and non-invasively by means of optical coherence tomography. A set of ten structural parameters was used to quantify biofilm structure, its development and change. The study focused on characterizing biofilm structure and development at the mesoscale (mm-range). Therefore, biofilm replicates (n = 10) were cultivated and analyzed. Three hypotheses were defined in order to estimate the effect of Fe2+ inflow concentration and/or wall shear stress on biofilm development and structure, respectively. It was not the intention to investigate and describe the underlying mechanisms of iron incorporation as this would require a different set of tools applied at microscopic levels as well as the use of, i.e., omic approaches. Fe2+ addition influenced biofilm development (e.g., biofilm accumulation) and structure markedly. Experiments revealed the accumulation of FeO(OH) within the biofilm matrix and a positive correlation of Fe2+ inflow concentration and biofilm accumulation. In more detail, independent of the wall shear stress applied during cultivation, biofilms grew approximately four times thicker at 2.5 mg Fe2+/L (44.8 µmol/L; high inflow concentration) compared to the low Fe2+ inflow concentration of 0.25 mg Fe2+/L (4.48 µmol/L). This finding was statistically verified (Scheirer–Ray–Hare test, ANOVA) and hints at a higher stability of Bacillus subtilis biofilms (e.g., elevated cohesive and adhesive strength) when grown at elevated Fe2+ inflow concentrations.

3D-printed tortuous vessels with Photodissociable and morphology-controllable ink

“…The comparison of the results of the three experiments showed that Na + , Fe 3+ and Fe 2+ did not affect cell activity, which was similar to the conclusion of previous studies. 38,54 This study demonstrated that the prepared curved vascular scaffold could be used to explore the mechanism of vascular tortuosity leading to lesions in vitro. The Fe 3+ ions introduced by immersion during the preparation and the Fe 2+ ions obtained by light reduction had no effect on the cellular activity.…”

“…The comparison of the results of the three experiments showed that Na + , Fe 3+ and Fe 2+ did not affect cell activity, which was similar to the conclusion of previous studies. 38,54…”

Analysis of Ca2+ and Fe2+ Ions in Ngade Water and Tolire Lake Water Ternate, North Maluku

“…The structure of calcium is very important in agricultural soil, because there is a complex adsorption of Ca 2+ ions in groundwater which must be quite high (Amin, 2016). The researchers have conducted research on liquid waste for the concentration of Fe 2+ in human water and other living things under certain conditions it requires iron (Fe) as a nutrient but excessive levels need to be avoided (Gierl et al, 2022;Eisele & Gabby, 2014;Ondigo et al, 2013). So far, several methods have been used to determine the concentration of Ca 2+ and Fe 2+ ions such as coagulation and adsorption in water but at a high cost and takes a long time (Ngteni et al, 2020;Mu et al, 2017;Tiwow et al, 2017;Zheng et al, 2020;Kyomugasho et al, 2017).…”