Investigating the Modes of Action of the Antimicrobial Chalcones BC1 and T9A

Luana G Morão,Dirk-Jan Scheffers,Lucia B Cavalca,Luis O Regasini,Mariana B Santos,Henrique Ferreira,Parichita Chakraborty,Caio Zamuner,Guilherme Dilarri,André S G Lorenzoni,Beatriz C Marques,Gabriela M Ayusso

doi:10.3390/molecules25204596

Luana G Morão, Dirk-Jan Scheffers + Show 10 more

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https://doi.org/10.3390/molecules25204596

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Xanthomonas citri subsp. citri (X. citri) is an important phytopathogen and causes Asiatic Citrus Canker (ACC). To control ACC, copper sprays are commonly used. As copper is an environmentally damaging heavy metal, new antimicrobials are needed to combat citrus canker. Here, we explored the antimicrobial activity of chalcones, specifically the methoxychalcone BC1 and the hydroxychalcone T9A, against X. citri and the model organism Bacillus subtilis. BC1 and T9A prevented growth of X. citri and B. subtilis in concentrations varying from 20 µg/mL to 40 µg/mL. BC1 and T9A decreased incorporation of radiolabeled precursors of DNA, RNA, protein, and peptidoglycan in X. citri and B. subtilis. Both compounds mildly affected respiratory activity in X. citri, but T9A strongly decreased respiratory activity in B. subtilis. In line with that finding, intracellular ATP decreased strongly in B. subtilis upon T9A treatment, whereas BC1 increased intracellular ATP. In X. citri, both compounds resulted in a decrease in intracellular ATP. Cell division seems not to be affected in X. citri, and, although in B. subtilis the formation of FtsZ-rings is affected, a FtsZ GTPase activity assay suggests that this is an indirect effect. The chalcones studied here represent a sustainable alternative to copper for the control of ACC, and further studies are ongoing to elucidate their precise modes of action.

Highlights

Brazil is the world leader in sweet orange production, exporting more than 80% of concentrated orange juice consumed in the world
We focus on the antimicrobial action of chalcones
X. citri (MICs of BC1 = 90 μg/mL, and T9A = 50 μg/mL) was slightly more resistant to the compounds when compared to B. subtilis and T9A = 50 μg/mL) was slightly more resistant to the compounds when compared to B. subtilis (BC1 = 50 μg/mL, and T9A = 40 μg/mL)

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Brazil is the world leader in sweet orange production, exporting more than 80% of concentrated orange juice consumed in the world. Citri, the causative agent of Asiatic Citrus. Canker (ACC), is a bacterial phytopathogen that can infect all the commercially important species of sweet orange, and is a major threat to the orange juice industry [1]. The most effective way to control the disease is to eradicate infected trees. Molecules 2020, 25, 4596 sprays of copper compounds to prevent the spread of X. citri in the orchards [2]. Spraying trees with copper-containing bactericides has led to the emergence of resistant strains [3]. Copper is stable and accumulates in the soil, which has a negative environmental impact [4]

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