Metabolic Footprints of Burkholderia Sensu Lato Rhizosphere Bacteria Active against Maize Fusarium Pathogens

Abstract

Consistent with their reported abundance in soils, several <i>Burkholderia</i> sensu lato strains were isolated from the rhizosphere of maize plants cultivated at different sites in central México. Comparative analysis of their 16S rRNA gene sequences permitted their separation into three distinctive clades, which were further subdivided into six other clusters by their close resemblance to (1) <i>Trinickia dinghuensis</i>; (2) <i>Paraburkholderia kirstenboschensis</i>, <i>P. graminis</i>, <i>P. dilworthii</i> and <i>P. rhynchosiae</i>; (3) <i>B. gladioli</i>; (4) <i>B. arboris</i>; (5) <i>B. contaminans</i>, or (6) <i>B. metallica</i> representative species. Direct confrontation assays revealed that these strains inhibited the growth of pathogenic <i>Fusarium oxysporum</i> f. sp. <i>radicis-lycopersici</i>, and <i>F. verticillioides</i> within a roughly 3-55% inhibition range. The use of a DIESI-based non-targeted mass spectroscopy experimental strategy further indicated that this method is an option for rapid determination of the pathogen inhibitory capacity of <i>Burkholderia</i> sensu lato strains based solely on the analysis of their exometabolome. Furthermore, it showed that the highest anti-fungal activity observed in <i>B. contaminans</i> and <i>B. arboris</i> was associated with a distinctive abundance of certain <i>m</i>/<i>z</i> ions, some of which were identified as components of the ornbactin and pyochelin siderophores. These results highlight the chemical diversity of <i>Burkholderia</i> sensu lato bacteria and suggest that their capacity to inhibit the <i>Fusarium</i>-related infection of maize in suppressive soils is associated with siderophore synthesis.