Burkholdines from Burkholderia ambifaria: Antifungal Agents and Possible Virulence Factors

Abstract

Burkholdines are cyclic lipopeptides with unusual antifungal potency, making them promising leads as a new class of antifungal agents. However, a recent report using knockout mutagenesis indicates that these and related compounds, such as occidiofungins, xylocandins, and cepacidines, may also be synonymous with the long-known hemolytic virulence factors found in diverse Burkholderia isolates. Because of their possible roles in causing Burkholderia infections or curing fungal infections, it is important to fully define their structures and biological activities using pure compounds. Here, we report the structures of three further burkholdines, Bk-1119, Bk-1213, and Bk-1215, which were elucidated using spectroscopic methods. The absolute configuration of this compound class was determined for the first time using a combination of spectroscopy and chemical degradation techniques. Antifungal and hemolytic activities were assessed for five pure burkholdines, representative of the structural diversity of this lipopeptide class. All of the burkholdines were potent antifungal and hemolytic agents, validating their probable role in virulence. However, one of the burkholdines (Bk-1119) exhibited a >30-fold selectivity for fungi versus sheep erythrocytes and was more than 25-fold more potent than amphotericin against some fungal strains. Therefore, burkholdines have potential to selectively target fungal infections.

Structure activity relationship study of burkholdine analogues toward simple antifungal agents

“…However, antifungal activities of these cyclic peptides were very weak against S. cerevisiae and A. oryzae in comparison with the Bk-analogue (2). In contrast, we found the linear peptide (36) has moderate antifungal activity.…”

Bioinformatic evaluation of the secondary metabolism of antistaphylococcal environmental bacterial isolates

“…The genus Stenotrophomonas, part of the Gammaproteobacteria, is a member of the same family (Xanthomonadales) as Lysobacter, which is well known for antibiotic production (Xie et al 2012). The Betaproteobacteria isolated (Delftia, Acidovorax, Variovorax, and Achromobacter) are all Burkholderiales, which have recently showcased their biosynthetic potential with the discovery of several new bioactive compounds from Burkholderia, including the burkholdines and burkholdacs, as well as the recent discovery by our laboratory of a PK-NRP hybrid metallophore, delftibactin, produced by D. acidovorans (Biggins et al 2011;Johnston et al 2013;Lin et al 2012;Tawfik et al 2010;Xie et al 2012). Chitinophaga is the only known Bacteroidetes antibiotic producer isolated; however, Bacteroidetes have a high percentage of PKS and NRPS genes relative to their genome size, second only to the Actinobacteria, which may indicate the other isolated Bacteroidetes have unrealized biosynthetic potential and are a potential source for antimicrobial discovery (Donadio et al 2007).…”

Initial Studies on the Lytic Effects of Burkholdines upon Mycotic Agents

“…Although a single purified burkholdine was not employed, to date all members of the burkholdine family produced by strain 2.2N have equal specific activity. 3,4 In the sonicated suspension used here, anti-yeast and anti-fungal activity would have been due to all related burkholdines; no synergistic activity has been demonstrated between individual burkholdines. 3,4 Killing of yeast cells as measured by decrease of colony-forming units coincided with the release of intracellular maltase and loss of viability ( Table 1).…”

“…3,4 In the sonicated suspension used here, anti-yeast and anti-fungal activity would have been due to all related burkholdines; no synergistic activity has been demonstrated between individual burkholdines. 3,4 Killing of yeast cells as measured by decrease of colony-forming units coincided with the release of intracellular maltase and loss of viability ( Table 1). The short time needed to exhibit killing, lysis, and loss of viability suggests that they reflect the primary result of burkholdine activity, not a secondary consequence of some other effect (e.g., ATP reduction).…”

“…One gram of the spray dried cells had an equivalent activity of 0.006gm of purified burkholdines 3,4 and had an MIC of 0.5µg/mL against S. cerevisiae and C. albicans and 1.0µg/mL against A. niger.…”