Production of Obionin A and Derivatives by the Sooty Blotch Fungus Microcyclospora malicola

Abstract

Introduction !Various members of the Ascomycetes order Capnodiales are known to form mycelial mats or fruiting bodies on the surface of epicuticular wax layers of apples that result in dark, flyspeck-like spots and sooty blemishes [1]. Although these fungi do not cause fruit destructing diseases or rots, sooty blotch and flyspeck (SBFS) fungi cause substantial economic damages. Stored apples may desiccate earlier during storage, and apples with dark smudges and blemishes have a reduced market quality [2]. Although sooty blotch fungi have early been associated with different kinds of mycelial types, only three species were distinguished as causal agents until the end of the 20th century [3]. A single species only was accepted as the causal agent of flyspeck. This situation changed dramatically when polyphasic taxonomic studies incorporated DNA sequence-based species recognition concepts, with the help of which at least 60 SBFS fungi were distinguished and numerous new species and genera described [4-6].Although different SBFS species can co-occur in the same orchard and even on the same apple, details of how they interact between each other or to host substrata and other fruit pathogens are hitherto little understood. During inventory studies for SBFS fungi in Slovenia, we observed that juxtaposed colonies of different SBFS fungi were clearly separated from each other on field-collected apples and that a selected strain of Microcyclospora tardicrescens inhibited the colony growth of the fruit pathogen Colletotrichum fioriniae in dual culture tests [7]. Bioassay-guided fractionation and subsequent structure elucidation yielded trichothecolone acetate and its novel (S)-7-hydroxy derivative as active principles for the interaction between M. tardicrescens and C. fioriniae. In this follow-up publication, we describe the investigation of an isolate of another sooty blotch species, Microcyclospora malicola, and its production of a series of bioactive pigments. Abstract !A multitude of sooty blotch and flyspeck fungi, mainly belonging to the Ascomycetes order Capnodiales, causes dark blemishes and flyspeck-like spots on apples worldwide. Different sooty blotch and flyspeck fungi can coexist in the same orchard and even on a single fruit. Our preceding experiments revealed an activity of Microcyclospora malicola strain 1930 against the anthracnose fungus Colletotrichum fioriniae in dual culture assays. Extracts of M. malicola strain 1930 showed a broad bioactivity against filamentous fungus Mucor hiemalis and gram-positive bacterium Bacillus subtilis. A bioactivity-guided isolation led to the identification of obionin A (1) as the main active principle. In addition to 1, which was previously isolated from the marine fungus Leptosphaeria obiones, we isolated three derivatives. Metabolite 2 bears a keto function at C-6, besides the replacement of oxygen by nitrogen at position 10. Two more derivatives are adducts (3, 4) of acetone as work-up artifacts. Because obionin A (1) and its derivative 2 showed cytotoxic effects and...

Laccaridione C, a Bioactive Polyketide from the Fungus Montagnula sp.

“…Obionins A and B, two structurally related molecules also having an ortho-benzoquinone ring system, were isolated from the marine-derived fungus Leptosphaeria obiones of the Pleosporales order [16] and from an unidentified fungus also belonging to the Pleosporales order [15], respectively. New obionin derivatives were also obtained from the Sooty Blotch fungus Microcyclospora malicola, an ascomycete of the order Capnodiales [13]. Although rare, the presence of this natural product family has been reported in terrestrial and marine fungal strains, Basidiomycetes and in two different orders of Ascomycetes, which raises the possibility of horizontal gene transference between these fungi.…”

“…R = OCH3 (3) R = OCH 2 CH 3 (4) R = H these bioactive pigmented polyketides also have potent protease inhibitory properties [6,[12][13][14][15], which is most likely the main mechanism of action of the bioactivity herein reported for 1.Biosynthetically, compound 1 is the intermediate stage between the C-11 dehydroxylated form of leptosphaerodione (4) and the C-11 methoxylated laccaridione A (2) or the C-11 ethoxylated laccaridione B (3).…”

Elsinopirins A–D, Decalin Polyketides from the Ascomycete Elsinoё pyri

“…However, some pigments belonging to the class of perylene quinones named elsinochromes had been reported previously from a different species of Elsinoё [ 4 , 5 ]. We recently found moderate antimicrobial effects in cultures of strain 2202C, which was identified as E. pyri in our ongoing studies on bioactive compounds from plant-associated Ascomycota [ 6 , 7 , 8 ]. To assess its potential for secondary metabolite production, strain 2203C was cultivated on potato-dextrose-agar (Carl Roth GmbH + Co. KG, Karlsruhe, Germany) plate medium; extracts showed the presence of five metabolites that were isolated using preparative high-performance liquid chromatography (HPLC) ( Figure 1 ).…”