Magnetite-Assisted Capture Affinity, Concentration Dependence, and Magnetic Extraction Rate of Bacillus cereus

Abstract

The interactions between magnetic nanoparticles (MNP) and bio-surfaces have impacted key industries such as food, biomedicine, water purification, and agriculture. Bacteria, with their diverse bio-surfaces, offer potential for such interactions. Yet, there is a paucity of research interpreting the dynamics behind bacteria-nanoparticle interactions. Advancing this knowledge could improve the industrial applications. Current research gaps include information about the magnetic nanoparticle-assisted concentration dependence of Bacillus cereus and determination of the rate of bacterial extraction by MNPs such as iron oxide nanoparticles (IONPs). Using magnetic IONPs as the choice of MNP, this study aimed to investigate in vitro the interactions between model bacteria and IONPs, leveraging the bacterial magnetising property. IONPs were synthesised by co-precipitation and characterised. Magnetic capture efficiency was reported for four model bacteria (Bacillus cereus, Escherichia coli, Staphylococcus aureus, and Salmonella typhimurium). The effect of particle concentration on the viability of Bacillus cereus and the rate of magnetic extraction of Bacillus cereus were evaluated. Bacillus cereus had the most robust interaction with IONP (90.34%). While the magnetic extraction was time-dependent, the average rate of magnetic extraction for Bacillus cereus was calculated as 3.617 CFU mL^-1/min. Growth inhibition at 1.0, 2.0, and 4.0 mg mL^-1 of IONP was significant. Magnetic capture results indicated that members of the Bacillus genus screened for plant growth-promoting traits may be suitable to combine with IONPs for future land application.

Keywords: Bacillus; bacterial capture; bacterial viability; interactions; iron oxide; nanoparticle.

Figure 1

Schematic diagram of assessing the bacterial capture (magnetic capture) for a concentration gradient of iron oxide nanoparticles. C₁−C₄ indicates the concentration gradient of iron oxide nanoparticles. The figure was created by Bio Render.

Figure 2

Percentage (%) bacterial capture (magnetic capture) at different concentrations of iron oxide nanoparticle for (a) Bacillus cereus; (b) E. coli; (c) Salmonella typhimurium; (d) Staphylococcus aureus. ns, not significant (p > 0.05); * p ≤ 0.05; ** p ≤ 0.01; *** p ≤ 0.001; **** p ≤ 0.0001. The error bars represent mean ± s.e.m., All the graphs consist of three independent biological replicates (n = 3).

Figure 3

Confirming magnetic extraction of B. cereus cells by plate assay.

Figure 4

(a) Concentration dependence of B. cereus with IONPs and the viability of bacterial cells after 18 h of incubation by CFU assay; (b) live/dead bacterial percentage upon exposure to IONPs. ** p ≤ 0.01, *** p ≤ 0.001; **** p ≤ 0.0001. The error bars represent mean ± s.e.m. The graph consists of three independent biological replicates (n = 3). (c) Growth curve of Bacillus cereus with IONPs after 12 h of incubation. The error bars represent mean ± s.d.

Figure 5

Schematic diagram: magnetic extraction of B. cereus at the onset (left), after 35 s (middle), and after 70 s (right). T indicates the time measured in seconds (s). IONPs are indicated in red colour and B.cereus cells are indicated in green colour. The figure was created by BioRender and Power point tool.

Figure 6

Time−dependent magnetic extraction of B. cereus. (a) Growth of B. cereus cells retained in the supernatant after magnetic decantation at each time interval in each serial dilution. (b) The graph depicts the retained bacterial cell concentration and magnetic yield vs. time of magnetic exposure. T indicates the time measured in seconds (s). CFU indicates colony-forming units. The error bars represent mean ± s.e.m. The graph consists of three independent biological replicates (n = 3).