Probing the viability of palladium‐challenged bacterial cells using flow cytometry

Abstract

BACKGROUND The ability of bacterial cells to retain membrane integrity and membrane potential when challenged with palladium (II) solution has not being examined previously, which would provide a platform towards the bio‐fabrication of a multifunctional tandem bio‐nanoparticles. This study investigates the use of flow cytometry coupled with fluorescent probes to determine membrane integrity and membrane potential of cells of Desulfovibrio desulfuricans and Bacillus benzeovorans challenged with 1 mmol L−1 of sodium tetrachloropalladate (II) (Na2PdCl4) solution at pH 2 followed by reduction of palladium (II) (Pd(II)) with formate to give 1 wt% loading of Pd(0) on the cells. RESULTS Fluorescently labelled active bacterial cells retained over 80% of membrane potential when challenged with Pd(II) solutions except for Bacillus benzeovorans (Bb) with about 32% retention. Cell viability was also seen to be variable and strain‐dependent while dead cells lack any membrane integrity. Since esterase activity is energy independent and unable to confirm the membrane potential of the bacterial cells, the dye 3,3′‐dihexyloxacarbocyanine iodide [DiO6(3)] was used to determine and confirm the membrane potential of the bacterial cells. CONCLUSION The results revealed that since fluorescently labelled bacterial cells containing Pd(0) can retain metabolic activity when analysed with flow cytometry, it provides the potential for combining chemical catalysis with biochemical activity in reactions that require metabolic synergy. © 2018 Society of Chemical Industry

Extracellular Electron Transfer by Shewanella oneidensis Controls Palladium Nanoparticle Phenotype

“…As MR-1 palladization increases the 600 nm light scattering signal for single cells, we hypothesized that cellular nanoparticle formation could be assessed by flow cytometry side scattering. To further probe the relationship between palladization and S. oneidensis viability, we used flow cytometry to simultaneously measure side scattering and fluorescence from a dye (propidium iodide, PI) that indicates membrane permeability of palladized bacteria. , At both 100 and 1000 μM Pd­(II), increases in side scatter were detected for palladized S. oneidensis strains, relative to a Pd-free control (Figure S6). At the higher Pd­(II) concentration, there was a corresponding increase in both side scatter and PI fluorescence, indicating the presence of a dead population that is highly palladized.…”

Synthesis of Pd/Ru Bimetallic Nanoparticles by Escherichia coli and Potential as a Catalyst for Upgrading 5-Hydroxymethyl Furfural Into Liquid Fuel Precursors

“…Bio-Pd/Au core shells form inside the bacterial cytoplasm (Supplementary Figure S1), which implies uptake and processing mechanisms for these heavy metals, that have no known biological function. Although the bacteria remain metabolically competent during Pd(0) “seeding,” as shown by the use of flow cytometry (Omajali et al, 2018), the routes by which the Pd(0) “seeds” are localized and then develop from initial Pd-nuclei is still unknown, despite that these are key to the patterning of the subsequent bimetallic. Following formation of the Pd “seeds” cell viability is lost rapidly, although hydrogenase activity persists for several hours (Mikheenko et al, 2008).…”

Novel catalytically active Pd/Ru bimetallic nanoparticles synthesized by Bacillus benzeovorans

“…S1 ) (as opposed to earlier reports of NP growth on bacterial cell surfaces) following deposition of Pd-NPs in the cytoplasm 7 implies cellular uptake and trafficking mechanism(s) for metals with no known biological roles. Flow cytometry studies have established metabolic activity following uptake of Pd(II) and its intracellular reduction to Pd(0) 8 . Intracellular localization of Pd NPs was also reported for the Gram-positive organism Bacillus benzeovorans , with co-localization of cytoplasmic Pd with phosphate groups (Supplementary Information Fig.…”