Novel nanoconjugates of metal oxides and natural red pigment from the endophyte Monascus ruber using solid-state fermentation

Abstract

Background: Antimicrobial resistance has emerged as a major global health threat, necessitating the urgent development of new antimicrobials through innovative methods to combat the rising prevalence of resistant microbes. With this view, we developed three novel nanoconjugates using microbial natural pigment for effective application against certain pathogenic microbes.

Results: A natural red pigment (RP) extracted from the endophyte Monascus ruber and gamma rays were applied to synthesize RP-ZnO, RP-CuO, and RP-MgO nanoconjugates. The synthesized nanoconjugates were characterized by different techniques to study their properties. The antimicrobial potential of these nanoconjugates was evaluated. Moreover, the antibiofilm, protein leakage, growth curve, and UV light irradiation effect of the synthesized nanoconjugates were also studied. Our results confirmed the nano-size, shape, and stability of the prepared conjugates. RP-ZnO, RP-CuO, and RP-MgO nanoconjugates showed broad antimicrobial potential against the tested bacterial and fungal pathogens. Furthermore, the RP-ZnO nanoconjugate possessed the highest activity, followed by the RP-CuO against the tested microbes. The highest % inhibition of biofilm formation by the RP-ZnO nanoconjugate. Membrane leakage of E. coli and S. aureus by RP-ZnO nanoconjugate was more effective than RP-MgO and RP-CuO nanoconjugates. Finally, UV light irradiation intensified the antibiotic action of the three nanoconjugates and RP-ZnO potential was greater than that of the RP-MgO, and RP-CuO nanoconjugates.

Conclusion: These findings pave the way for exploiting the synthesized nanoconjugates as potential materials in biomedical applications, promoting natural, green, and eco-friendly approaches.

Keywords: Monascus ruber; Antibiofilm; Antimicrobial; Metal oxide; Nano-conjugates; Red pigment.

Fig. 1

HR-TEM images of the synthesized RP-MgO (a), RP-CuO (b), and RP-ZnO (c) nanoconjugates

Fig. 2

SEM images of the synthesized RP-MgO (a), RP-CuO (b), and RP-ZnO (c) nanoconjugates

Fig. 3

UV–Vis spectra (a), XRD patterns (b), and FTIR spectra (c) of the synthesized RP-MgO, RP-CuO, and RP-ZnO nanoconjugates

Fig. 4

Schematic representation of the synthesis mechanism of the RP-MgO, RP-CuO, and RP-ZnO nanoconjugates. The figure was created in BioRender.com

Fig. 5

Antibiofilm potential of RP-MgO, RP-CuO, and RP-ZnO nanoconjugates against some bacteria (a), and some bacteria, and unicellular fungi (b)

Fig. 6

Effect of RP-MgO, RP-CuO, and RP-ZnO nanoconjugates on growth curves of S. aureus (a) and E. coli (b), and the protein leakage from cell membranes of S. aureus (c) and E. coli (d)

Fig. 7

The UV effect on the antibacterial activity of RP-MgO, RP-CuO, and RP-ZnO nanoconjugates against S. aureus (a), the magnified part (b), and E. coli (c), the magnified part (d)

Fig. 8

Schematic representation of antimicrobial activity mechanisms (1, 2, 3, and 4) of RP-MgO, RP-CuO, and RP-ZnO nanoconjugates. The figure was created in BioRender.com