A Quinoline Antibiotic from Rhodococcus erythropolis JCM 6824

Abstract

A new quinoline antibiotic, aurachin RE, was isolated and identified from a culture broth of Rhodococcus erythropolis JCM 6824. The aurachin RE structure was determined based on NMR and mass spectrometric analysis. The structure is similar to that of aurachin C antibiotics that have been identified from Stigmatella aurantiaca. Compared to aurachin C, however, aurachin RE exhibits a wide and strong antimicrobial spectrum against both high-and low-GC Gram-positive bacteria.Keywords Actinobacteria, antibiotic, aurachin, quinoline, Rhodococcus Large numbers of antibiotics have been isolated from the Actinobacteria, including those from the genera, Streptomyces and Nocardia. Recently, we have reported the genus Rhodococcus is also a prolific antibiotic producer [1]. At least, five species and 18 strains of Rhodococcus have been demonstrated to exhibit anti-microbial activity. R. erythropolis, in particular, includes three groups of strains that produce respective antibiotics [1]. One of the antibiotic-producing strains, R. erythropolis JCM 6824, and also the partially purified antibiotic isolated from this strain, exhibits strong antibiotic against a broad range of Gram-positive bacteria. Further investigations on the metabolites of this strain have resulted in the isolation of a new quinoline antibiotic compound designated aurachin RE [1a; IUPAC name: 1-hydroxy-2-methyl-3-(3,7,11-trimethyldodeca-9-hydroxy-2,6,10-trienyl)quinolin-4-one]. In this paper, we report on the isolation, structure elucidation, and biological properties of this compound.R. erythropolis JCM 6824 was cultured in W-minimal medium [2] supplemented with succinate (0.2%, w/v), sucrose (0.2%, w/v), and casamino acids (0.2%, w/v). Stock seed cultures (10 6 cfu/ml) were maintained at Ϫ80°C in 10% glycerol. A 600-m l aliquot of stock seed was transferred into each of six 2-liters baffled Erlenmeyer flasks containing 600 ml of the culture medium. The fermentation was carried out on a rotary shaker at 28°C for 28 hours with agitation of 120 rpm.The fermentation broth (3.6 liters) was centrifuged and any residual cells in the supernatant were removed by membrane filtration (0.2-m m pore size). The filtered supernatant was applied to a C18 cartridge column (SepPak ® Vac 35 cc; Waters, Milford, MA), and the column was sequentially washed with 100 ml of 20% EtOH and 30 ml of 50% EtOH. The sample was eluted with 20 ml of EtOH and then evaporated to dryness. The residue was J. Antibiot. 61 (11) Aurachin RE (1a) and aurachin C (1b: H instead of 9Ј-OH)

Menaquinone biosynthesis inhibition: a review of advancements toward a new antibiotic mechanism

“…Most of this work has been pioneered by Kurosu et al 17 and Debnath et al 37 who have based much of their efforts on the creation of structures with similar SARs to aurachin RE, a natural product that shows bactericidal activity through a proposed dual mechanism of MenA and respiratory MIC (mg/mL) chain inhibition. 38 Debnath et al 37 have been able to synthesise over 400 molecules of interest with >95% purity which have been screened in bacterial growth inhibitory assays, with varying results. The compounds synthesised have been based around a benzophenone core structure, with a highly varied lipophilic side chain substitution.…”

Discovery of Selective Menaquinone Biosynthesis Inhibitors against Mycobacterium tuberculosis

“…In an attempt at finding a new pharmacophore for MenA inhibitors, we recently identified a new quinolone natural product, aurachin RE ( 1 , Figure 3), 27 which exhibited MenA enzyme inhibitory activity as well as a wide antimicrobial spectrum against Gram-positive bacteria. As there is an overall structural resemblance between aurachin RE and our 1 st generation MenA inhibitors (e.g.…”

Cloning and Heterologous Expression of the Aurachin RE Biosynthesis Gene Cluster Afford a New Cytochrome P450 for Quinoline N‐Hydroxylation

“…It is particularly interesting that two phylogenetically unrelated species of microorganisms produce such highly structurally related secondary metabolites. Although aurachin biosynthesis genes ( aua genes) have been identified in Stigmatella, 8 our preliminary PCR screening study, based on the nucleotide and amino acid (aa) sequence data for aua , failed to identify the corresponding genes in the Rhodococcus genome 5. These results suggested that this Rhodococcus strain does not contain aua ‐type biosynthesis genes or biosynthesis genes similar to those that were isolated from Stigmatella .…”

“…We had previously isolated a new quinoline antibiotic—aurachin RE ( 1 , Scheme ), classified as group I—from a culture broth of R. erythropolis JCM 6824 5. The structure of an aurachin basically consists of a quinolone ring and a farnesyl chain, and the structure of aurachin RE is closely related to that of aurachin C (H instead of 9′‐OH), which was isolated from Stigmatella aurantiaca Sg a15 6.…”