When validating the antimicrobial screens, the variability and reproducibility revealed remarkable low inter- and intra-assay CVs, which indicates low media batch variation and an excellent opportunity to detect also weak antimicrobial activity. The only exception was the growth variability of C. In total, 54 fungi including 12 Aspergilli and 30 Penicillia strains were treated with six SCs and screened for novel antimicrobial compounds in four fractions.
All fungi were grown in the same medium and kept under constant conditions to avoid influence of biotic and abiotic factors on the expression of secondary metabolites. The high number of Aspergilli and Penicillia strains was chosen due to the large amount of genomic, proteomic, and ecological data available for these genera. In addition, recent studies showed that even closely related fungi share only a small number of similar secondary metabolites and that horizontal gene transfer of biosynthesis clusters of secondary metabolites is a scarce event [ 31 , 32 ].
We detected 30 samples of treated fungi belonging to six different genera, with seven Penicillia strains among them, which reduced significantly growth of the test organism compared to the untreated fungal samples.
All SCs used in this study effected the production of antimicrobial compounds at least in one fungus. However, whether the effect of the SC on the production of antimicrobial compounds is due to epigenetic modulation in the specific fungus must still be investigated.
Interestingly, except for A. Furthermore, growth was inhibited either of yeast, gram positive, or gram negative bacteria except A. This is in line with recent findings that SCs are target specific, inducing specific secondary metabolite production [ 16 , 33 ]. Excluding A. The small number of fungal fractions displaying activity against gram negative bacteria underlines the poor availability of antibiotics against gram negative bacteria and underlines that few novel candidates are in the pipeline [ 34 ].
In the supernatant of untreated and treated A. Both the antimicrobial activity and cytotoxicity were increased if this fungus was grown in the presence of all SCs. These findings are in line with one of our studies, which shows that the SCs increased, among other mycotoxins, patulin production in A.
In addition, the crude supernatant of H. It has been described that H. Our observation that also the addition of NO increases the antimicrobial activity of H. At present, it is unknown if NO influences chromatin structure in fungi; therefore, further research is needed to study the role of NO in the regulation of secondary metabolite production.
The finding that specific SCs increase the production of specific secondary metabolites like patulin and presumably koninginins highlights that small mass chemicals potentially inducing epigenetic modulation could be used for biotechnological approaches to increase the yield of specific compounds.
Since A. Apart from A. Optimization of biotic and abiotic factors, for example, temperature, light, pH, nutrients, and oxygen availability, which are known to influence production of SM [ 40 ], could increase the yield of the antimicrobial compounds. Furthermore, there are indications that the age of the spores influences the production of antimicrobial compounds [ 41 ].
This is in line with our finding that, for example, in O. Therefore, optimization of the age of spores could also increase the yield of antimicrobial compounds. The observation that the pellet of P. No antimicrobial compounds active against gram positive bacteria have yet been described in any P. It is known that P. However, no antimicrobial activity against C.
Whether butyrate acts as an epigenetic modulator generally in fungi including P. We observed that growth of S. In two of these cases supernatant of GlcNac treated P. However, we cannot fully exclude that the specific SC also downregulates metabolites, which are used by S.
Taken together, the high number of antimicrobial active fungal samples in this study underlines the potential of this approach, combining treatment of fungi with small chemicals with a sensitive screening tool. This results in approximately 10— samples which are taken to further isolation and identification [ 44 ]. Our study comprising samples of 54 fungi detected 14 fungal samples containing potential novel antimicrobial compounds, which will be isolated and characterized in future studies.
Compared to the estimated gain of 0. This indicates a large number of so far unknown antimicrobial compounds in already screened and characterized fungi which are accessible through to potential epigenetic regulation. The diversity of the antimicrobial hits in the initial screen indicates that every presumable fungus, even well described fungi, has the potential to produce novel antimicrobial compounds that warrant discovery.
In general, epigenetic modification of fungi could reduce the risk of rediscovery of known compounds. Furthermore, the used method combining treatment of fungi with small chemicals with a sensitive screening tool can easily be upscaled for high-throughput screening programs, discovering novel antimicrobial natural products.
The authors declare that there is no conflict of interests regarding the publication of this paper. Table S1: Different growth dynamics of S. Figure S1: Growth of S. Figure S2 shows the influence of spore maturation on the production of antimicrobial compounds in O.
This is an open access article distributed under the Creative Commons Attribution License , which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Article of the Year Award: Outstanding research contributions of , as selected by our Chief Editors.
Read the winning articles. Journal overview. Special Issues. Received 07 Mar Revised 16 Jun Accepted 18 Jun Published 09 Jul Abstract For decades, fungi have been the main source for the discovery of novel antimicrobial drugs. Introduction For decades, one of the main sources for the discovery of novel antimicrobial drugs has been the screening of fungal cultures for bioactive natural compounds [ 1 , 2 ]. Materials and Methods 2. ITS Rhizopus oryzae R. Table 1. Table 2.
Intra- and inter-assay coefficient of variation CV of biological and technical replicates. Extracted supernatant Butyrate C. Table 3. Fungal samples showing increased antimicrobial activity after SC treatment compared to the untreated fungal sample. Figure 1. Control comprises S. Figure 2. Antimicrobial activity of the pellet of P. Figure 3. Antimicrobial activity against C. Controls comprise C. Figure 4. Figure 5. Cytotoxic effects of the supernatant of A.
Control comprises Moser medium. Supplementary Materials. References G. Newman and G. Winter, S. Behnken, and C. Walsh and M. Keller, G. Turner, and J. Fisch, A. Nutritional immunology. Nutritional metabolomics. Precision nutrition. Industrial Biotechnology. Research topics. Carbohydrate-active enzymes.
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Our activities. Getting involved. Antibiotics are chemicals that kill or inhibit the growth of bacteria and are used to treat bacterial infections. They are produced in nature by soil bacteria and fungi. This gives the microbe an advantage when competing for food and water and other limited resources in a particular habitat, as the antibiotic kills off their competition. An antibiotic can also be classified according to the range of pathogens against which it is effective.
Penicillin G will destroy only a few species of bacteria and is known as a narrow spectrum antibiotic. Tetracycline is effective against a wide range of organisms and is known as a broad spectrum antibiotic.
Bacteria are termed drug-resistant when they are no longer inhibited by an antibiotic to which they were previously sensitive. The emergence and spread of antibacterial-resistant bacteria has continued to grow due to both the over-use and misuse of antibiotics. If a strain of a bacterial species acquires resistance to an antibiotic, it will survive the treatment. As the bacterial cell with acquired resistance multiplies, this resistance is passed on to its offspring.
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