Resumo

Functional analyses of gentisate and protocatechuate ring-cleavage pathways and hydroxybenzoates peripheral routes in Burkholderia xenovorans LB400 Romero-Silva, María José, Agulló, Loreine and Seeger, Michael. Laboratorio de Microbiología Molecular y Biotecnología Ambiental, Departamento de Química and Center for Nanotechnology and System Biology, Universidad Técnica Federico Santa María, Valparaíso, Chile. michael.seeger@usm.cl Aromatic compound including environmental pollutants are widely distributed in ecosystems. Bacteria from Burkholderiales order are commonly able to degrade a large number of aromatic compounds. Burkholderia xenovorans strain LB400 is a model bacterium for the degradation of PCBs and other aromatic compounds. In this study, a survey on functional catabolic pathways for hydroxylated benzoates by B. xenovorans LB400 is presented. In silico analysis of strain LB400, indicated the presence in the genome of genes encoding the gentisate and protocatechuate central pathways and 3-hydroxybenzoate (3-HBA) and 4-hydroxybenzoate (4-HBA) peripheral pathways. Gentisate and protocatechuate are key intermediates in the aerobic catabolism of a variety of aromatic compounds including 3-HBA and 4-HBA. Growth studies showed that strain LB400 is able to use 3-HBA, 4-HBA, gentisate and protocatechuate as sole carbon source. In order to determinate the role of gentisate and protocatechuate catabolic pathways in the degradation of 3-HBA and 4-HBA in strain LB400, transcriptional analyses of genes encoding key aromatic dioxygenases and related hydroxylases were performed. The expression of the mhbD gene encoding the gentisate 1,2-dioxygenase was observed in 3-HBA-grown cells. The expression of the pcaG gene encoding the protocatechuate 3,4-dioxygenase alpha subunit was observed during growth on 4-HBA. The mhbM gene encoding the 3-HBA hydroxylase was transcribed during growth on 3-HBA, whereas the pobA gene encoding the 4-HBA hydroxylase was expressed during growth on 4-HBA. These results showed functional dioxygenase- and hydroxylase-encoding genes and indicate the involvement of gentisate and protocatechuate central pathways in 3-HBA and 4-HBA degradation by strain LB400. Gentisate1,2-dioxygenase activity was observed in crude extract of cells grown on 3-HBA. A high protocatechuate dioxygenase activity was measured during growth of strain LB400 on 4-HBA. These results indicated that in B. xenovorans LB400 3-HBA and 4-HBA are channeled into gentisate and protocatechuate central pathways. This study extends the wide aromatic catabolic repertoire of B. xenovorans strain LB400. Acknowledgements: FONDECYT (1110992, 1070507 and 7100027) and USM (131109 and 130948) grants.