Magnesium Oxide Nanoparticles: Effective Agricultural Antibacterial Agent Against Ralstonia solanacearum

Abstract

Magnesium (Mg) is an essential mineral element for plants and is nontoxic to organisms. In this study, we took advantage of nanotechnologies to systematically investigate the antibacterial mechanisms of magnesium oxide nanoparticles (MgONPs) against the phytopathogen Ralstonia solanacearum (R. solanacearum) in vitro and in vivo for the first time. R. solanacearum has contributed to catastrophic bacterial wilt, which has resulted in the world-wide reduction of tobacco production. The results demonstrated that MgONPs possessed statistically significant concentration-dependent antibacterial activity, and the minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) were measured as 200 and 250 μg/mL, respectively. Additional studies, aimed at understanding the toxicity mechanism of MgONPs, indicated that physical injury occurred to the cell membranes, along with decreased motility and biofilm formation ability of R. solanacearum, due to the direct attachment of MgONPs to the surfaces of the bacterial cells, which was observed by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Reactive oxygen species (ROS) accumulation could also be an important reason for the antibacterial action, inducing DNA damage. The toxicity assessment assay under greenhouse conditions demonstrated that the MgONPs had exerted a large effect on tobacco bacterial wilt, reducing the bacterial wilt index. Altogether, the results suggest that the development of MgONPs as alternative antibacterial agents will become a new research subject.

Comparative Study on the Fungicidal Activity of Metallic MgO Nanoparticles and Macroscale MgO Against Soilborne Fungal Phytopathogens

“…The electrostatic interaction might mediate the excellent nanoparticle-cell aggregates, which can be observed in previous reports regarding the antibacterial activities of a series of nanoparticles (Chen et al, 2016a,b;Pan et al, 2013). Indeed, our previous studies have found that nMgO and graphene were visibly directly attached to phytopathogens, affecting energy metabolism and cell membrane potential (Cai et al, 2018a). Ideally, adsorption of nMgO on fungal cells could disturb membrane potential as a result of enhanced adherence.…”

“…Enhanced adherence to pathogens of antifungal drugs was caused by decreased electric repulsive forces (Miyake et al, 1990). Consequently, nanoparticles could be capable of physically damaging the cell envelope, which was confirmed by SEM and TEM imaging above (Sharma et al, 2015;Cai et al, 2018a).…”

“…For mMgO, an intact cell envelope under cytoplasmic disorder was observed, especially in P. nicotianae cells, with hardly recognizable organelles (Figures 8D,H). It seems that the nMgO inactivate the fungi by injuring the cell plasmalemma originating from the direct physical interaction, as in bacteria (Cai et al, 2018a). This means that the inactivation of hyphae was ascribed to some irreversible toxicity behaviors caused by nMgO, including vacuolation and disorganized enterocytes, which are associated with nanoparticle attachment and penetration, as represented by the triangle arrowhead in Figures 8C,G. In contrast, fungal cells have a normal structure and not quite severely inordinate cytoplasm.…”

“…In particular, Huang et al, further demonstrated that peptide linkages in the bacterial cell wall are physically damaged by the generation of superoxide ions on the surface of nMgO (Huang et al, 2005). Conceivably, nMgO have enormous potential as antibacterial agents, effectively suppressing agricultural bacterial and fungal diseases caused by Ralstonia solanacearum, a medical and foodborne pathogen (Jin and He, 2011;Parizi et al, 2014;Imada et al, 2016;Sierra-Fernandez et al, 2017;Cai et al, 2018a). Nonetheless, investigations on the effects of nMgO on fungal pathogens and on elaborate antimycotic mechanisms have scarcely been reported before (Jin and He, 2011).…”

“…Most importantly, for the purpose of green and sustainable agriculture, a perfect agricultural microbicide would have no phytotoxicity on plants. Excitedly, foliar application of nMgO as nanoscale fertilizers or light absorption promoters significantly promoted the growth of several crops (Imada et al, 2016;Cai et al, 2018a). Typically, tobacco black shank and black root rot are widespread in Chongqing and significantly decrease tobacco quality and yield (Zhang et al, 2003;Huang and Kang, 2010).…”