Bacterial-mediated teranostics is a new paradigm in medical technology. In a recent article in the journal ACS Applied Biomaterials, researchers synthesized gold (Au) nanocumulus in the cell wall of Lactobacillus rhamnosus that gave them photoluminescence properties.
Study: Hierarchical passage of gold nanocumulus in living bacteria. Image credit: Kateryna Kon / Shutterstock.com
The team observed that the nanocumulus was passed down from generation to generation. However, new generations have lost their luminescence with the agglomeration of nanocumulus. The present work discusses the role of the bacterial cell wall in the aggregation of nanoclusters.
Bacteria-mediated teranostics
An ideal vehicle in drug delivery encapsulates the load or can act as a therapeutic agent on its own. In addition, drug vehicles addressed the host’s immune response challenges, targeting, and specificity. Genetically engineered bacteria and nanomaterial-based drugs are effective in killing tumors. Nanoparticle-laden living bacteria are considered non-viral gene delivery systems. Near-infrared (NIR) radiation-induced gene expression was made possible by the use of photothermal metal nanoparticles.
Attenuated facultative anaerobic bacteria help to develop scheduled delivery vehicles that can promote cytotoxicity at the tumor site. Listeria monocytogenes, Bifidobacterium and Salmonella typhimurium are some bacterial species used as self-propelled delivery systems. In addition, intestinal bacteria are of therapeutic importance as they influence the tumor microenvironment and affect treatment outcomes.
Bacteria-mediated therapy allows the combination of nanomaterials with molecular drugs for effective teranostic. A convenient way to develop these therapeutic agents is to synthesize nanoparticles into the bacterial cell wall and subsequently load drug molecules into nanoparticles. However, peptidoglycan prevents nanoparticles from binding to the surface of the bacterial cell wall. Therefore, a solid strategy for synthesizing nanoparticles in the bacterial cell wall and an understanding of their fate in new generations of bacteria is needed.
At nanoclusters in Lactobacillus rhamnosus
In the present work, the authors synthesized Au nanoclusters on Lactobacillus rhamnosus (MTCC 1408) by chemical reduction. They observed the formation of luminescent clusters on the bacterial cell walls while keeping the bacteria alive. In addition, the clusters clustered into spherical structures of 100 to 200 nanometers without transforming into plasmonic Au nanoparticles in the bacterial cell wall. The team studied up to six subcultures in depth to understand the involvement of nanoparticle bacteria in the medical field.
Research results
The synthesis of Au nanoclusters was observed in the bacterial cell wall under an ultraviolet (UV) transilluminator. Nanocumulus appeared as orange luminescent structures. As the bacteria spread, the color systematically decreased from the first subculture to later cultures. Observation of bacterial cultures under the UV-visible (vis) spectrum revealed the presence of a broad peak between 200 and 400 nanometers and the absence of a peak at 520 nanometers that is characteristic of Au nanoparticles.
Bacterial protein amino acid residues peaked at 420 nanometers and were persistent throughout subcultures. The peak of 580 nanometers corresponding to Au nanoclusters disappeared in the first and subsequent subcultures of bacteria.
X-ray photoelectron (XPS) spectroscopy of Au cells with Au nanocluster (Lac_AuNC) revealed the presence of Au (0) peaks at 83.2 and 87.2 electronvolts, respectively. Lac_AuNC confocal laser scanning microscopy (CLSM) supported cluster formation and revealed a characteristic orange emission under 405 nanometer lasers.
The authors observed that the individual bacterium appeared as luminescent orange structures, suggesting the connection of Au nanocumulus to bacteria. The descending bacteria showed luminescence for a minimum of 12 hours, which was lost in the first and subsequent subcultures.
Transmission electron microscopy (TEM) images of the droplet drop from the product medium revealed bacteria with nanoparticles with a particle size of 1.3 ± 0.4 nanometers. In addition, the Au nanocumulus distributed by the bacterial body was revealed by the use of elementary maps performed with energy dispersive X-ray spectroscopy (EDS).
Field emission scanning electron microscope (FESEM) studies in the product medium revealed the presence of bacteria, and Au nanoclusters in the bacterial cell wall showed a characteristic photoluminescence that was absent in the control. Lactobacillus rhamnosus.
In addition, atomic force microscopy (AFM) studies revealed greater roughness in Lac_AuNC than in control bacteria, suggesting the presence of nanocumulus on the surface of the bacterial cell wall.
Conclusion
In conclusion, the authors developed a new technique for generating photoluminescent Au nanocumulus on the outer cell walls of living bacteria. They observed that later generations that received the nanocumulus passed as non-luminescent agglomerated particles containing Au.
The results revealed that the cell wall peptidoglycans received by next-generation bacteria helped carry the nanocumulus. The elongation of the cell wall during bacterial division caused the formation of larger particles in the new generations.
During elongation and bacterial division, the luminescence of nanoclusters is lost without the formation of plasmonic Au nanoparticles. Through the present study, the authors demonstrated a new way to understand the passage of nanoparticles to the next generation and explored their biomedical applications.
Reference
Debasmita, D., Ghosh SS, Chattopadhyay, A. Hierarchical Passage of Gold Nanoclusters in Living Bacteria. ACS Applied Bio Materials (2022) .https: //pubs.acs.org/doi/10.1021/acsabm.2c00315https: //pubs.acs.org/doi/10.1021/acsabm.2c00315
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