Characterization of a strain of Pseudomonas fluorescens that solubilizes phosphates in vitro and produces high antibiotic activity against Mycobacterium tuberculosis

Martha Trujillo¹, Silvia Miguélez¹, Encarna Velázquez¹, M. Sol Jiménez², Pedro F. Mateos¹ and Eustoquio Martínez-Molina¹

¹Departamento de Microbiología y Genética, Facultad de Farmacia, Edificio Departamental, Universidad de Salamanca, Salamanca 37007, SPAIN.

²Laboratorio de referencia de Micobacterias. Servicio de Bacteriología. Centro Nacional de Microbiología. Madrid, SPAIN.

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The genus Pseudomonas is known as a P-solubilizer and antibiotic producer. In this work we have characterized a strain, PFBV1, which actively solubilizes phosphate in vitro and produces several antibiotics with high activity against several microorganisms, including Mycobacterium tuberculosis. Using phenotypic characteristics and LMW RNA profiles, we identified this strain as Pseudomonas fluorescens. Many strains of this species produce “in vitro” antibiotic activity against several microorganisms, but this strain only produces antibiotic activity in the presence of Cu²⁺ at relatively high concentrations. The antibiotics produced by the isolate PFBV1 have a wide antimicrobial spectrum, including Gram negative bacteria such as Proteus vulgaris; Gram positive bacteria including Bacillus subtilis, Staphylococcus aureus, Mycobacterium phlei and Mycobacterium tuberculosis; ascomycetous yeasts such as Candida albicans and basidiomycetous yeasts such as Cryptococcus albidus. Column fractionation in Sephacryl S200 using water as eluent showed the existence of two peaks corresponding to different molecules (A and B) with antibiotic activity against Bacillus subtilis. The production of molecule B is absolutely dependent of the presence of Cu²⁺ in the culture medium. This antibiotic showed high activity against all the strains tested and mainly against virulent strains of Mycobacterium tuberculosis isolated from a patient with tuberculosis.