Evaluation of the biocontrol potential of Pseudomonas protegens against Colletotrichum sp. by the induction of hydrogen cyanide synthesis

Abstract

The growing demand for food, aligned with the need for sustainable agriculture, has led to the discovery of alternative ways to control plant diseases, such as biological control by microorganisms. It is noteworthy the ability of the bacterium Pseudomonas protegens, through its secondary metabolites, to control the development of phytopathogens, such as Colletotrichum spp., which causes anthracnose in several crops. The objective of this work was to evaluate the biotechnological potential of P. protegens through a scientometric analysis and, experimentally, the biocontrol potential against Colletotrichum sp. by inducing the synthesis of hydrocyanic acid (HCN). First, to elucidate the potential and studies of P. protegens related to scientific studies, a scientometric analysis was performed. The database used was the Web of Science (WoS) Core Collection, with data related to the period from 2011 to March 2024. Secondly, experimentally the agronomical potential as a biocontrol agent of P. protegens was determined by the synthesis of HCN. The functional genomic annotation of the microorganism was performed to determine the presence of the gene cluster of interest (hcnABC) and the analysis of the metabolic pathway. In the fermentation processes, the concentration of the HCN inducer (glycine) was tested in solid and liquid fermentation at concentrations of 1, 3, 5, 7, and 10 g/L, and the result was qualified by reaction with the picric acid solution and quantified by spectrometry using a potassium cyanide curve. The biocontrol action against Colletotrichum sp. was evaluated by competitive growth on PDA plates and the percentage of mycelial inhibition of the fungus was evaluated. The research about P. protegens in the database WoS and the posterior analysis resulted in 248 studies, with data from 2011 to March 2024. The first publication about P. protegens was in May 2011, which differentiated the species and evaluated the potential of its secondary metabolites. Switzerland and Germany were the countries with the highest centrality, 0.37 each. Among the areas reported, the microbiological area with a focus on agriculture stood out and the biological control research had the greatest prominence. The synthesis of hydrogen cyanide was maximized when using the highest concentration of the inducer tested (10 g/L of glycine) in both liquid and solid fermentation. In this case, the concentration of this metabolite in the solid medium was confirmed with a concentration equal to 0.084 mg of HCN, whereas in liquid fermentation a concentration of 0.043 mg of hydrocyanic acid was obtained. In the bioassays, this condition allowed the best biocontrol of Colletotrichum sp. with a fungal growth control of 65%. The scientometric analysis observed the biotechnological potential of P. protegens, mainly in agriculture, allowing its application in biological control. The presence of the hcnABC gene cluster in the genome of the bacterial isolate studied and its activity in the presence of its inducer (glycine) were demonstrated, allowing the synthesis of HCN and contributing to the biocontrol of Colletotrichum sp. in vitro. Thus, it is concluded that biotechnology has a high potential to promote the development of sustainable agriculture.