Xanthoepocin, a photolabile antibiotic of Penicillium ochrochloron CBS 123823 with high activity against multiresistant gram-positive bacteria

Abstract

Background With the steady increase of antibiotic resistance, several strategies have been proposed in the scientific community to overcome the crisis. One of many successful strategies is the re-evaluation of known compounds, which have been early discarded out of the pipeline, with state-of-the-art know-how. Xanthoepocin, a polyketide widespread among the genus Penicillium with an interesting bioactivity spectrum against gram-positive bacteria, is such a discarded antibiotic. The purpose of this work was to (i) isolate larger quantities of this metabolite and chemically re-evaluate it with modern technology, (ii) to explore which factors lead to xanthoepocin biosynthesis in P. ochrochloron, and (iii) to test if it is beside its known activity against methicillin-resistant Staphylococcus aureus (MRSA), also active against linezolid and vancomycin-resistant Enterococcus faecium (LVRE)—a very problematic resistant bacterium which is currently on the rise. Results In this work, we developed several new protocols to isolate, extract, and quantify xanthoepocin out of bioreactor batch and petri dish-grown mycelium of P. ochrochloron. The (photo)chemical re-evaluation with state-of-the-art techniques revealed that xanthoepocin is a photolabile molecule, which produces singlet oxygen under blue light irradiation. The intracellular xanthoepocin content, which was highest under ammonium-limited conditions, varied considerably with the applied irradiation conditions in petri dish and bioreactor batch cultures. Using light-protecting measures, we achieved MIC values against gram-positive bacteria, including methicillin-resistant Staphylococcus aureus (MRSA), which were up to 5 times lower than previously published. In addition, xanthoepocin was highly active against a clinical isolate of linezolid and vancomycin-resistant Enterococcus faecium (LVRE). Conclusions This interdisciplinary work underlines that the re-evaluation of known compounds with state-of-the-art techniques is an important strategy in the combat against multiresistant bacteria and that light is a crucial factor on many levels that needs to receive more attention. With appropriate light protecting measures in the susceptibility tests, xanthoepocin proved to be a powerful antibiotic against MRSA and LVRE. Exploring the light response of other polyketides may be pivotal for re-introducing previously discarded metabolites into the antibiotic pipeline and to identify photosensitizers which might be used for (antimicrobial) photodynamic therapies.

Genome sequencing and molecular networking analysis of the wild fungusAnthostomella pineareveal its ability to produce a diverse range of secondary metabolites

“…5a and 5b). The feature was matched to xanthoepocin, a polyketide antibiotic originally isolated from Penicillium simplicissimum and commonly found in other Penicillium species [70,71]. We also found a related node which showed a negative mass difference of 18.011, consistent with loss of a water molecule from xanthoepocin which happens already at MS 1 level (Additional files 4 and 6, Fig 5a).…”

“…Xanthoepocin has a homodimeric structure composed of two napthopyrone scaffolds, typically associated with pigmentation and sporulation in fungi and with a wide range of biological activities [72–74]. Xanthoepocin in particular has been shown to possess potent antibiotic activity against Gram-positive bacteria, including resistant strains of E. faecium and MRSA [71]. Informed by these findings, we performed antimicrobial plate assays with the same extracts that we used for the LC-MS analysis.…”

“…Our investigation revealed that the fungus possesses a rich biosynthetic machinery and can produce a wide variety of small molecules, particularly sesquiterpenoids and sesquiterpene lactones. Through spectral library matches, we putatively identified 14 sesquiterpenes and sesquiterpene lactones and one bis-napthopyrone polyketide with antibiotic activity which is currently being re-evaluated for biological testing [71]. For the latter, we also identified the putative BGC and proposed a step-by-step biosynthetic mechanism based on its chemical structure and the predicted activities of the BGC enzymes.…”

Light in the box - photobiological examination chamber with light trap ventilation system for studying fungal surface cultures illustrated with Metarhizium brunneum and Beauveria brongniartii

“…These contrasting results, i.e., no green light effect in M. robertsii [29] versus green light effect in M. brunneum (present study), might be rooted in the use of different growth media as the nutritional status can be decisive for the photoresponse [4,37,53]. However, since the whole genus Metarhizium seems to be devoid of opsins [8], the observed, distinct green light responses are somewhat puzzling.…”

Unveiling the Microbial Diversity and Associated Secondary Metabolism on Black Apples

“…Outside of the 15 strains selected for OSMAC analysis were other secondary metabolites from other fungal species detected in black apples, namely: mycophenolic acid, a highly biologically-active metabolite found Penicillium brevicompactum and other fungi,(56–58) aurofusarin, from the wheat pathogen Fusarium sp.,(59), enniatins from F. culmorum , the structurally-related xanthoepocin, a common metabolite from the Penicillium genus,(60, 61) asperphenamate, derived from several Aspergillaceae,(62–66) and berkedrimane A originally described from a P. solitum strain. (67) However, we speculate that the latter strain was misidentified, since we have never found berkedrimanes to be produced by any P. solitum strain.…”