Abstract
An endophytic bacterium inhibiting pathogenic bacteria was isolated and the strain was genetically identified as Paenibacillus polymyxa. Biochemical characterization of fermentation broth indicated the presence of peptidic antimicrobial molecules. Liquid-liquid partition resulted in an organic fraction (OF) and an aqueous fraction (AF). OF presented a broad spectrum of activity against a panel of pathogenic bacteria and a fungus whereas the AF was active only against Gram-negative bacteria. AF was sequentially submitted to ion-exchange, desalting and reverse phase (RP) chromatography. A molecule with an RT of 2.45 min exhibited activity against all Gram-negative pathogenic strains tested beside P. mirabilis. The primary structure of the molecule, named AMP-Pp, was determined as Gly-Glu-Hyp-Gly-Ala by N-terminal sequencing. The molecular mass and amino acid sequence were confirmed by MS/MS. With a molecular mass of 463 Da, AMP-Pp is one of the smallest active natural peptides reported, yet. RP chromatography of OF resulted in four peaks. The first three peaks corresponded to known antimicrobials. MS analysis of peak 4 revealed the presence of an ion with m/z 3,376.4 Da, whose proposed molecular formula is C182H321N29O29. The compound, named polycerradin, showed a spectrum of activity against Gram-positive bacteria, Gram-negative bacteria (beside P. mirabilis) and a fungus.
Highlights
Drug resistance in bacteria, the appearance of life-threatening viruses, and the increase in the incidence of fungal infections in the world’s population primed researchers to find novel molecules to prevent and treat human diseases (Ratti et al 2008)
A bacterium isolated from the leaves of a Prunus spp. present in the Brazilian Cerrado was identified by 16S rRNA analysis
A similarity score of 99.2% between the 16S rRNA sequence and database sequence indicated that the isolate belonged to Paenibacillus polymyxa
Summary
The appearance of life-threatening viruses, and the increase in the incidence of fungal infections in the world’s population primed researchers to find novel molecules to prevent and treat human diseases (Ratti et al 2008). Endophytic microorganisms that colonize internal plant tissues do so without causing negative effects but at the same time produce bioactive compounds. Those are relatively unstudied but could represent a potential source of novel natural antimicrobials. The Brazilian savannah, known as Cerrado, is the second-richest biome on Earth in terms of biodiversity (Sano et al 2010) This biome presents a huge concentration of different endemic plants (10,000 plant species) (Myers et al 2000). In this ecosystem, Brazilian savannah trees are excellent specimens to search for endophytic bacteria producing antimicrobial
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