Morphological changes of Fusarium oxysporum induced by CF66I, an antifungal compound from Burkholderia cepacia

Drug discovery through the isolation of natural products from Burkholderia

Introduction: The increasing threat of antibiotic-resistant pathogens makes it imperative that new antibiotics to combat them are discovered. Burkholderia is a genus of Gram-negative, non-sporulating bacteria. While ubiquitous and capable of growing within plants and groundwater, they are primarily soil-dwelling organisms. These include the more virulent forms of Burkholderia such as Burkholderia mallei, Burkholderia pseudomallei, and the Burkholderia cepacia complex (Bcc).Areas covered: This review provides a synopsis of current research on the natural products isolated from the genus Burkholderia. The authors also cover the research on the drug discovery efforts that have been performed on the natural products derived from Burkholderia.Expert opinion: Though Burkholderia has a small number of pathogenic species, the majority of the genus is avirulent and almost all members of the genus are capable of producing useful antimicrobial products that could potentially lead to the development of novel therapeutics against infectious diseases. The need for discovery of new antibiotics is urgent due to the ever-increasing prevalence of antibiotic-resistant pathogens, coupled with the decline in the discovery of new antibiotics.

Identification of volatile compounds produced by the bacterium Burkholderia tropica that inhibit the growth of fungal pathogens

It has been documented that bacteria from the Burkholderia genera produce different kinds of compounds that inhibit plant pathogens, however in Burkholderia tropica, an endophytic diazotrophic and phosphate-solubilizing bacterium isolated from a wide diversity of plants, the capacity to produce antifungal compounds has not been evaluated. In order to expand our knowledge about Burkholderia tropica as a potential biological control agent, we analyzed 15 different strains of this bacterium to evaluate their capacities to inhibit the growth of four phytopathogenic fungi, Colletotrichum gloeosporioides, Fusarium culmorum, Fusarium oxysporum and Sclerotium rolffsi. Diverse analytical techniques, including plant root protection and dish plate growth assays and gas chromatography-mass spectroscopy showed that the fungal growth inhibition was intimately associated with the volatile compounds produced by B. tropica and, in particular, two bacterial strains (MTo293 and TTe203) exhibited the highest radial mycelial growth inhibition. Morphological changes associated with these compounds, such as disruption of fungal hyphae, were identified by using photomicrographic analysis. By using gas chromatography-mass spectroscopy technique, 18 volatile compounds involved in the growth inhibition mechanism were identified, including α-pinene and limonene. In addition, we found a high proportion of bacterial strains that produced siderophores during growth with different carbon sources, such as alanine and glutamic acid; however, their roles in the antagonism mechanism remain unclear.

A Burkholderia cepacia complex non-ribosomal peptide-synthesized toxin is hemolytic and required for full virulence

Members of the Burkholderia cepacia complex (Bcc) have recently gained notoriety as significant bacterial pathogens due to their extreme levels of antibiotic resistance, their transmissibility in clinics, their persistence in bacteriostatic solutions, and their intracellular survival capabilities. As pathogens, the Bcc are known to elaborate a number of virulence factors including proteases, lipases and other exoproducts, as well as a number of secretion system associated effectors. Through random and directed mutagenesis studies, we have identified a Bcc gene cluster capable of expressing a toxin that is both hemolytic and required for full Bcc virulence. The Bcc toxin is synthesized via a non-ribosomal peptide synthetase mechanism, and appears to be related to the previously identified antifungal compound burkholdine or occidiofungin. Further testing shows mutations to this gene cluster cause a significant reduction in both hemolysis and Galleria mellonella mortality. Mutation to a glycosyltransferase gene putatively responsible for a structural-functional toxin variant causes only partial reduction in hemolysis. Molecular screening identifies the Bcc species containing this gene cluster, of which several strains produce hemolytic activity.