The Pbo Cluster from <i>Pseudomonas syringae</i> pv. Phaseolicola NPS3121 Is Thermoregulated and Required for Phaseolotoxin Biosynthesis
Lizeth Guardado-Valdivia,
Alejandra Chacón-López,
Jesús Murillo,
Jorge Poveda,
José Luis Hernández-Flores,
Luis Xoca-Orozco,
Selene Aguilera
Affiliations
Lizeth Guardado-Valdivia
Laboratorio Integral de Investigación en Alimentos, Departamento de Química y Bioquímica, Tecnológico Nacional de México, Instituto Tecnológico de Tepic, 63175 Nayarit, Mexico
Alejandra Chacón-López
Laboratorio Integral de Investigación en Alimentos, Departamento de Química y Bioquímica, Tecnológico Nacional de México, Instituto Tecnológico de Tepic, 63175 Nayarit, Mexico
Jesús Murillo
Institute for Multidisciplinary Research in Applied Biology (IMAB), Universidad Pública de Navarra (UPNA), Edificio de Agrobiotecnología, Avda. de Pamplona 123, 31192 Mutilva Baja, Spain
Jorge Poveda
Institute for Multidisciplinary Research in Applied Biology (IMAB), Universidad Pública de Navarra (UPNA), Edificio de Agrobiotecnología, Avda. de Pamplona 123, 31192 Mutilva Baja, Spain
José Luis Hernández-Flores
Centro de Investigación y Estudios Avanzados del IPN, Departamento de Ingeniería Genética, Irapuato, 36821 Guanajuato, Mexico
Luis Xoca-Orozco
Departamento de Ingeniería Bioquímica, Instituto Tecnológico Superior de Purísima del Rincón, Purísima del Rincón, 36413 Guanajuato, Mexico
Selene Aguilera
Laboratorio Integral de Investigación en Alimentos, Departamento de Química y Bioquímica, Tecnológico Nacional de México, Instituto Tecnológico de Tepic, 63175 Nayarit, Mexico
The bean (Phaseolus vulgaris) pathogen Pseudomonas syringae pv. phaseolicola NPS3121 synthesizes phaseolotoxin in a thermoregulated way, with optimum production at 18 °C. Gene PSPPH_4550 was previously shown to be thermoregulated and required for phaseolotoxin biosynthesis. Here, we established that PSPPH_4550 is part of a cluster of 16 genes, the Pbo cluster, included in a genomic island with a limited distribution in P. syringae and unrelated to the possession of the phaseolotoxin biosynthesis cluster. We identified typical non-ribosomal peptide synthetase, and polyketide synthetase domains in several of the pbo deduced products. RT-PCR and the analysis of polar mutants showed that the Pbo cluster is organized in four transcriptional units, including one monocistronic and three polycistronic. Operons pboA and pboO are both essential for phaseolotoxin biosynthesis, while pboK and pboJ only influence the amount of toxin produced. The three polycistronic units were transcribed at high levels at 18 °C but not at 28 °C, whereas gene pboJ was constitutively expressed. Together, our data suggest that the Pbo cluster synthesizes secondary metabolite(s), which could participate in the regulation of phaseolotoxin biosynthesis.
