Functionalization of magnetotactic bacteria with gold Nanoprisms. A Route to novel photothermal agents

Magnetotactic bacteria offer promising biomedical applications due to their unique ability to synthesize magnetic nanoparticles and their natural magnetotaxis, which enables their controlled navigation in fluids. They also serve as a platform for integrating synthetic nanomaterials, adding new functionalities and increasing their potential in biomedicine. This study explores the functionalization of Magnetospirillum gryphiswaldense (MSR-1) with gold nanoprisms (AuNPR). The attachment of AuNPR to the outer surface of MSR-1 was achieved by two synthetic approaches: i) direct attachment of AuNPR to MSR-1 to produce MSR-AuNPR and ii) pre-coating AuNPR with exopolysaccharides (EPS) from Lactobacillus plantarum (Lp) or Pseudomonas aeruginosa (Pa), resulting in Lp@AuNPR and Pa@AuNPR, which were then bound to MSR-1, thereby producing MSR-Lp@AuNPR and MSR-Pa@AuNPR. When exposed to near-infrared (NIR) light (λ = 1064 nm), the functionalized bacteria were able to produce a temperature increase ranging from 8 °C to 10 °C, thereby substantiating their capacity for photothermal therapy. Viability of the functionalized bacteria was also studied. While MSR-1 viability exhibited a greater decrease upon direct AuNPR attachment, EPS-coated AuNPR were able to decrease this toxic effect. This finding suggests that EPS coatings enhance bacterial compatibility and system stability. The study also confirmed that the release of AuNPR from MSR-1 remained minimal under biological pH conditions, indicating a high degree of conservation of the MSR-AuNPR, MSR-Lp@AuNPR, and MSR-Pa@AuNPR systems. Furthermore, the structural integrity of the functionalized bacteria was maintained after prolonged storage at 4 °C. These results underscore the augmented biomedical potential of magnetotactic bacteria functionalized with AuNPR for photothermal therapy, a combination that integrates their mobility given their intrinsic magnetic properties with an innovative NIR-responsive pathway. • Gold nanoprisms (AuNPR) were attached to the surface of Magnetospirillum gryphiswaldense (MSR-1) using two methods. • AuNPR-functionalized MSR-1 samples demonstrated potential for photothermal therapy (PTT). • EPS-coated AuNPR improved MSR-1 viability, compatibility and stability. • Systems showed low AuNPR-release under biological conditions and stability during cold storage.