Antiamoebins, myrocin B and the basis of antifungal antibiosis in the coprophilous fungus Stilbella erythrocephala (syn. S. fimetaria)

Antiamoebins I, III and XVI as well as several others in minor amounts were produced by four strains of the coprophilous fungus Stilbella erythrocephala (syn. S. fimetaria) in its natural substrate and in liquid culture. The total antiamoebin concentration in dung was 126-624 microg g(-1) fresh weight, with minimum inhibitory concentrations against most other coprophilous fungi being at or below 100 microg mL(-1). Myrocin B, not previously described from S. erythrocephala, was also produced, but only at low, nonfungicidal levels (< 5.3 microg g(-1)). No other antifungal substances were detected. It is concluded that antiamoebins are responsible for antibiosis in dung colonized by S. erythrocephala.     

Compatibility of Phloxine B, an Insecticidal Photoactive Dye, with Selected Biocontrol Fungi

The incorporation of the photoactive red food dye, phloxine B, into integrated pest management strategies has been suggested for the control of various insect pests. Inclusion of such a chemical pest control agent may interfere with a microbial pest control agent. Thus, representative fungi with potential for biocontrol were tested for their responses to phloxine B (0.01%) at different temperatures. Growth rates at selected temperatures were inhibited by dye in the presence of light for Coniothyrium minitans and Verticillium lecanii. Trichoderma virens growth was inhibited in light and dark. At optimal growth temperatures, Beauveria bassiana growth was inhibited only by the photoactivated dye species, while growth of Stilbella erythrocephala was not affected by the dye even in the presence of light.     

Sequences of stilboflavin C: towards the peptaibiome of the filamentous fungus Stilbella (= Trichoderma) flavipes

Filamentous fungi of the genus Stilbella are recognized as an abundant source of naturally occurring α‐aminoisobutyric acid‐containing peptides. The culture broth of Stilbella (Trichoderma) flavipes CBS 146.81 yielded a mixture of peptides named stilboflavins (SF), and these were isolated and separated by preparative TLC into groups named SF‐A, SF‐B, and SF‐C. Although all three of these groups resolved as single spots on thin‐layer chromatograms, HPLC analysis revealed that each of the groups represents very microheterogeneous mixtures of closely related peptides. Here, we report on the sequence analysis of SF‐C peptides, formerly isolated by preparative TLC. HPLC coupled to QqTOF‐ESI‐HRMS provided the sequences of 10 16‐residue peptides and five 19‐residue peptides, all of which were N‐terminally acetylated. In contrast to the previously described SF‐A and SF‐B peptaibols, SF‐C peptaibols contain Ser‐Alaol or Ser‐Leuol, which are rarely found as C‐termini, and repetitive Leu‐Aib‐Gly sequences, which have not been detected in peptaibols before. Taking the previously determined sequences of SF‐A and SF‐B into account, the entirety of peptides produced by S. flavipes (the ‘peptaibiome’) approaches or exceeds 100 non‐ribosomally biosynthesized peptaibiotics. Copyright © 2016 European Peptide Society and John Wiley & Sons, Ltd.     

Stilbella aciculosa: A Potential Biocontrol Fungus against Rhizoctonia solani

A semi‐solid fermentation product of the potential biocontrol fungus Stilbella aciculosa was formulated on wheat bran: water (1:1, w/w) and incubated 5, 10 and 15 days before addition to soil infested with the pathogen Rhizoctonia solani. Generally, preparations did not reduce survival of the pathogen in infested beet seed but they did prevent saprophytic growth of the pathogen from beet seed into soil. The magnitude of reduction by the 15‐day‐old inoculum was greater than that by the 5‐day‐old inoculum. Ten‐day‐old bran preparations of S. aciculosa at rates of 0.5 and 1.0% (w/w) in soil prevented post‐emergence damping‐off of cotton, radish and sugar beet in the glasshouse and a rate of 1.0% gave stands similar to those in the non‐infested control soil. The antagonist, grown on perlite formulated with molasses, cornmeal, alfalfa tissue or corn stover, prevented damping‐off of cotton in a naturally infested soil. However, the stands were not as great as that in soil planted with pentachloronitrobenzene (PCNB)‐treated seed. Toxic metabolites, produced by S. aciculosa developing on various substrates, slightly inhibited the growth of R. solani in culture and induced cytoplasmic leakage of the pathogen mycelium.     

Marine fungus <Emphasis Type="Italic">Stilbella aciculosa</Emphasis> as a potential producer of prostaglandins

The amount and composition of fatty acids in the fungus Stilbella aciculosa associated with the marine macroorganism Apostichopus japonica (trepang) were determined by gas-liquid chromatography and gas chromatography-mass spectrometry. In the culture liquid of S. aciculosa, prostaglandins (PG) of groups E and F were revealed by UV spectroscopy. This finding was confirmed by the presence of direct precursors of PG, polyunsaturated eicosapentaenoic and docosahexaenoic acids, in the culture liquid. The biomass of this fungus contained PG of group B.     

Sequences of polypeptide antibiotics stilboflavins, natural peptaibol libraries of the mold Stilbella flavipes.

From the culture broths of the mold Stilbella flavipes CBS 146.81, a mixture of polypeptides could be isolated by adsorption on XAD polystyrene resin and purified by Sephadex LH-20 chromatography. Using preparative thin-layer chromatography (TLC) three groups of peptides, named stilboflavins (SF) A, B, and C could be separated. Each of the groups showed microheterogeneity when investigated by high-performance liquid chromatography (HPLC). Employing on-line HPLC-electrospray ionization tandem mass spectrometry in the positive and negative ionization mode, together with gas chromatography-selected ion monitoring mass spectrometry, enantioselective GC and quantitative amino acid analysis, the sequences of stilboflavins A and B could be determined. Exchange of Glu in stilboflavins A peptides (acidic) against Gln in stilboflavins B peptides (neutral) is the rational for different polarity of the peptide groups and their separatability by TLC. Since SF A and B are bioactive N-acetylated 20-residue peptides with a high proportion of alpha-aminoisobutyric acid and C-terminal bonded amino alcohols (either leucinol, isoleucinol or valinol) the peptides belong to the group of peptaibol antibiotics.