Silver nanoclusters with Ag2+/3+ oxidative states are a new highly effective tool against phytopathogenic bacteria

Abstract

The main measure worldwide adopted to manage plant bacterial diseases is based on the application of copper compounds, which are often partially efficacious for the frequent appearance of copper-resistant bacterial strains and have raised concerns for their toxicity to the environment and humans. Therefore, there is an increasing need to develop new environmentally friendly, efficient, and reliable strategies for controlling plant bacterial diseases, and among them, the use of nanoparticles seems promising. The present study aimed to evaluate the feasibility of protecting plants against attacks of gram-negative and gram-positive phytopathogenic bacteria by using electrochemically synthesized silver ultra nanoclusters (ARGIRIUM‑SUNCs®) with an average size of 1.79 nm and characterized by rare oxidative states (Ag2+/3+). ARGIRIUM‑SUNCs strongly inhibited the in vitro growth (effective concentration, EC50, less than 1 ppm) and biofilm formation of Pseudomonas syringae pv. tomato and of quarantine bacteria Xanthomonas vesicatoria, Xylella fastidiosa subsp. pauca, and Clavibacter michiganensis subsp. michiganensis. In addition, treatments with ARGIRIUM‑SUNCs also provoked the eradication of biofilm for P. syringae pv. tomato, X. vesicatoria, and C. michiganensis subsp. michiganensis. Treatment of tomato plants via root absorption with ARGIRIUM‑SUNCs (10 ppm) is not phytotoxic and protected (80%) the plants against P. syringae pv. tomato attacks. ARGIRIUM‑SUNCs at low doses induced hormetic effects on P. syringae pv. tomato, X. vesicatoria, and C. michiganensis subsp. michiganensis as well as on tomato root growth. The use of ARGIRIUM‑SUNCs in protecting plants against phytopathogenic bacteria is a possible alternative control measure. Key points • ARGIRIUM‑SUNC has strong antimicrobial activities against phytopathogenic bacteria; • ARGIRIUM‑SUNC inhibits biofilm formation at low doses; • ARGIRIUM‑SUNC protects tomato plants against bacterial speck disease.

Combat phytopathogenic bacteria employing Argirium-SUNCs: limits and perspectives

“…Through a transcriptomic approach carried out on the P. syringae pv. tomato strain used in the study of Orfei et al ( 2023a ), whose genome we recently sequenced (Orfei et al 2023b ) to better perform the transcriptomic analysis, we demonstrated that the exposition of bacterial cells for 10 and 30 min at sub-letal doses of Argirium - SUNCs induced change in the expression of genes associated with transporters ( e . g ., CadA P-type ATPase, the arsenite resistance efflux pump, multidrug resistance proteins), iron homeostasis ( e .…”

“…The recent results we obtained with the nanomaterial silver ultra nanoclusters (< 2 nm) ( Argirium - SUNCs ® ), published in Applied Microbiology and Biotechnology (Orfei et al 2023a ), seem to open up new perspectives in the chemical control of plant bacterial diseases, which will be described in the present minireview.…”

“…In fact, at very low concentrations (< 1 ppm), Argirium - SUNCs show strong antimicrobial and antibiofilm activities against Gram-negative ( Pseudomonas syringae pv. tomato, Xanthomonas vesicatoria and Xylella fastidiosa ) and Gram-positive ( Clavibacter michiganensis ) phytopathogenic bacteria (Orfei et al 2023a ) as well as mammalian pathogenic ones (Pompilio et al 2018 ), and common pathogenic and spoilage food bacteria (Mancusi et al 2024 ), while, in general, the antibacterial activity of AgNPs ranges between 10 and 100 ppm (Duval et al 2019 ) (Table 1 ).…”

“…The use of agrochemicals is notoriously inefficient as, for example, a large fraction of the 2.5 million tons of pesticides applied per year are either lost to the air and run-off or unable to effectively reach target (Rodrigues et al 2017 ). In this context, Orfei et al ( 2023a ) demonstrated that application of Argirium - SUNCs during the hydroponic grown of tomato significantly protected leaves from bacterial speck disease caused by P. syringae pv. tomato.…”

The In Vitro Antibacterial Activity of Argirium SUNc against Most Common Pathogenic and Spoilage Food Bacteria

“…The spread of microorganisms multi-resistant to antibiotics has reached significant numbers, so much so that the development of substances with innovative antimicrobial activity appears to be an urgent necessity. Argirium SUNc ® could be proposed as such, as, to date, there are no formulations on the market that present a broad effectiveness at a low concentrations (<2.5 ppm) and with little environmental impact [39][40][41][42][43][44]. In fact, they are synthesized using patented methods (EU-Pathent) which involve the use of biocompatible ingredients; consequently, the introduction of harmful substances is not foreseen and the concentrations in use do not exceed the limits established by laws.…”