Abstract
The bacterial strain, EMM-1, was isolated from the rhizosphere of red maize (“Rojo Criollo”) and identified as Pseudomonas protegens EMM-1 based on phylogenetic analysis of 16S rDNA, rpoB, rpoD, and gyrB gene sequences. We uncovered genes involved in the production of antimicrobial compounds like 2,4-diacetylphloroglucinol (2,4-DAPG), pyoluteorin, and lectin-like bacteriocins. These antimicrobial compounds are also produced by other fluorescent pseudomonads alike P. protegens. Double-layer agar assay showed that P. protegens EMM-1 inhibited the growth of several multidrug-resistant (MDR) bacteria, especially clinical isolates of the genera Klebsiella and β-hemolytic Streptococcus. This strain also displayed inhibitory effects against diverse fungi, such as Aspergillus, Botrytis, and Fusarium. Besides, a crude extract of inhibitory substances secreted into agar was obtained after the cold-leaching process, and physicochemical characterization was performed. The partially purified inhibitory substances produced by P. protegens EMM-1 inhibited the growth of Streptococcus sp. and Microbacterium sp., but no inhibitory effect was noted for other bacterial or fungal strains. The molecular weight determined after ultrafiltration was between 3 and 10 kDa. The inhibitory activity was thermally stable up to 60°C (but completely lost at 100°C), and the inhibitory activity remained active in a wide pH range (from 3 to 9). After treatment with a protease from Bacillus licheniformis, the inhibitory activity was decreased by 90%, suggesting the presence of proteic natural compounds. All these findings suggested that P. protegens EMM-1 is a potential source of antimicrobials to be used against pathogens for humans and plants.
Highlights
Microorganisms have developed diverse strategies to survive and compete for the resources of their habitat, and one of them is the production of inhibitory substances [1]
We report the identification of P. protegens EMM-1, a strain isolated from the “Rojo Criollo” maize rhizosphere
A new antagonistic bacterium isolated from the rhizosphere of “Rojo Criollo” maize, was identified as P. protegens EMM-1 after phylogenetic analysis
Summary
Microorganisms have developed diverse strategies to survive and compete for the resources of their habitat, and one of them is the production of inhibitory substances [1]. Pseudomonads are Gram-negative γ-proteobacteria, highly competitive due to the production of several inhibitory compounds [2]. Pseudomonas protegens represents a new bacterial group that stands out for its ability to produce diverse inhibitory substances, including pyoluteorin (Plt), pyrrolnitrin (Prn), 2,4-diacetylphloroglucinol (2,4-DAPG), and hydrogen cyanide [6, 7]. P. protegens produces LlpA bacteriocins [9], capable of inhibiting some phytopathogenic Pseudomonas. These bacteriocins likely provide P. protegens with competitive advantages in the rhizosphere [2]
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