Cepabactin

Burkholderia pseudomallei is a mostly saprophytic bacterium, but can infect humans where it causes the difficult-to-manage disease melioidosis. Even with proper diagnosis and prompt therapeutic interventions mortality rates still range from >20% in Northern Australia to over 40% in Thailand. Surprisingly little is yet known about how B. pseudomallei infects, invades and survives within its hosts, and virtually nothing is known about the contribution of critical nutrients such as iron to the bacterium's pathogenesis. It was previously assumed that B. pseudomallei used iron-acquisition systems commonly found in other bacteria, for example siderophores. However, our previous discovery of a clinical isolate carrying a large chromosomal deletion missing the entire malleobactin gene cluster encoding the bacterium's major high-affinity siderophore while still being fully virulent in a murine melioidosis model suggested that other iron-acquisition systems might make contributions to virulence. Here, we deleted the major siderophore malleobactin (mba) and pyochelin (pch) gene clusters in strain 1710b and revealed a residual siderophore activity which was unrelated to other known Burkholderia siderophores such as cepabactin and cepaciachelin, and not due to increased secretion of chelators such as citrate. Deletion of the two hemin uptake loci, hmu and hem, showed that Hmu is required for utilization of hemin and hemoglobin and that Hem cannot complement a Hmu deficiency. Prolonged incubation of a hmu hem mutant in hemoglobin-containing minimal medium yielded variants able to utilize hemoglobin and hemin suggesting alternate pathways for utilization of these two host iron sources. Lactoferrin utilization was dependent on malleobactin, but not pyochelin synthesis and/or uptake. A mba pch hmu hem quadruple mutant could use ferritin as an iron source and upon intranasal infection was lethal in an acute murine melioidosis model. These data suggest that B. pseudomallei may employ a novel ferritin-iron acquisition pathway as a means to sustain in vivo growth.

Antimicrobial resistance in Gram-negative pathogens represents a global threat to human health. This study determines the antimicrobial potential of a taxonomically and geographically diverse collection of 263 Burkholderia (sensu lato) isolates and applies natural product dereplication strategies to identify potentially novel molecules. Antimicrobial activity is almost exclusively present in Burkholderia sensu stricto bacteria and rarely observed in the novel genera Paraburkholderia, Caballeronia, Robbsia, Trinickia, and Mycetohabitans. Fourteen isolates show a unique spectrum of antimicrobial activity and inhibited carbapenem-resistant Gram-negative bacterial pathogens. Dereplication of the molecules present in crude spent agar extracts identifies 42 specialized metabolites, 19 of which represented potentially novel molecules. The known identified Burkholderia metabolites include toxoflavin, reumycin, pyrrolnitrin, enacyloxin, bactobolin, cepacidin, ditropolonyl sulfide, and antibiotics BN-227-F and SF 2420B, as well as the siderophores ornibactin, pyochelin, and cepabactin. Following semipreparative fractionation and activity testing, a total of five potentially novel molecules are detected in active fractions. Given the molecular formula and UV spectrum, two of those putative novel molecules are likely related to bactobolins, and another is likely related to enacyloxins. The results from this study confirm and extend the observation that Burkholderia bacteria present exciting opportunities for the discovery of potentially novel bioactive molecules.

·Metal chelation has found many applications that directly affect human's life.·Natural siderophores are one of the most potent chelators for Fe (III)·1-Hydroxypyridine-2-one (1,2-HOPO) (Fig. 1a), which is shown in 4-carboxy-1-hydroxypyridin-2-one (1,2-HOPO-4-COOH) (Fig. 1b), is a moiety that electronically resembles the hydroxamate group found in natural siderophores (Fig. 1c). Of note, 1,2-HOPO moiety is present in the natural siderophore cepabactin [1]·Synthesis of 1,2-HOPO containing chelators has been carried in solid phase using carboxylic acid derivatives of 1,2-HOPO and required the protection of the reactive hydroxyl group usually with benzyl group (Bzl). After the peptide elongation, the Bzl group has been removed on the same solid phase using a bit harsh conditions: 0.1 M BBr3 in DCM for 60 min [2], 10% HBr in AcOH for 14 h [3]; in solution: 1 M BCl3 in DCM for 2 d [4], 50% HCl in AcOH for 4 d [5], H2-Pd/C, AcOH-MeOH [6].·First of all, a method for the incorporation of the 1,2-HOPO-4-COOH through its carboxyl group into the peptide backbone without protecting the N-OH is proposed (the presence of the carboxyl group facilitates the attachment).·Furthermore, in the cases that Bzl protection is required for the N-OH, a friendlier method for removing the Bzl is described. The removal of the Bzl is done concomitantly to the global deprotection and cleavage of the peptide from the resin using TFA- TFMSA-H2O (8:3:1).