Mediation of Bacterial and Fungal Secondary Metabolites in Agro-Environmental Interactions

A special issue of Microorganisms (ISSN 2076-2607). This special issue belongs to the section "Environmental Microbiology".

Deadline for manuscript submissions: closed (30 July 2021) | Viewed by 16479

Special Issue Editors


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Guest Editor
Council for Agricultural Research and Economics (CREA), Agriculture and Environment Center (AA), Rome, Italy
Interests: beneficial native bacteria; soil; water; functional genes; microbial ecology; honey bee associated bacteria; microbiome; ecosystem services

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Co-Guest Editor
Council for Agricultural Research and Economics (CREA), Agriculture and Environment Center (AA), Rome, Italy
Interests: root-colonizing fungi; biodiversity; rhizosphere; secondary metabolites; growth promotion; fungal toxins; microbial indicators

Special Issue Information

Dear Colleagues,

The key role of microbial secondary metabolites for cell survival under nutrient limited conditions is widely recognized. Metabolites of microbial origin are also receiving increasing attention in the frame of the continuous search for sources of new natural products and bioactive compounds. In agricultural systems (i.e., cropping systems and honey bee hives), bacterial and fungal secondary metabolites mediate numerous beneficial and pathogenic interactions, such as plant growth promotion, plant-pathogen interactions, or protection against honey bee pathogens. The functional role of the natural microbiota in controlling pathogens of agricultural interest, often remains un-exploited. The genes encoding the biosynthetic pathways of secondary metabolites may be used as functional markers to investigate the biosynthetic potential of bioactive molecule production, but further research is needed for translating results into practice.

The aim of this Special Issue of Microorganisms is to present an array of different case studies where the biological role of metabolites of microbial origin is investigated in the context of solving agro-environmental issues. Applied research investigation studies are welcome.

Dr. Maria Ludovica Saccà
Dr. Luisa Maria Manici
Guest Editors

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Keywords

  • natural products
  • secondary metabolites
  • biosynthetic potential
  • functional genes
  • bioactive molecules

Published Papers (5 papers)

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Research

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14 pages, 2994 KiB  
Article
Antiviral Property of the Fungal Metabolite 3-O-Methylfunicone in Bovine Herpesvirus 1 Infection
by Filomena Fiorito, Claudia Cerracchio, Maria Michela Salvatore, Francesco Serra, Alessia Pucciarelli, Maria Grazia Amoroso, Rosario Nicoletti and Anna Andolfi
Microorganisms 2022, 10(1), 188; https://doi.org/10.3390/microorganisms10010188 - 15 Jan 2022
Cited by 9 | Viewed by 1697
Abstract
Bovine herpesvirus type-1 (BoHV-1) is a widespread pathogen that provokes infectious rhinotracheitis and polymicrobial infections in cattle, resulting in serious economic losses to the farm animal industry and trade restrictions. To date, non-toxic active drugs against BoHV-1 are not available. The exploitation of [...] Read more.
Bovine herpesvirus type-1 (BoHV-1) is a widespread pathogen that provokes infectious rhinotracheitis and polymicrobial infections in cattle, resulting in serious economic losses to the farm animal industry and trade restrictions. To date, non-toxic active drugs against BoHV-1 are not available. The exploitation of bioactive properties of microbial products is of great pharmaceutical interest. In fact, fungi are a promising source of novel drugs with a broad spectrum of activities and functions, including antiviral properties. Hence, the potential antiviral properties of 3-O-methylfunicone (OMF), a secondary metabolite produced by Talaromyces pinophilus, were evaluated on BoHV-1. In this study, during BoHV-1 infection in bovine cells (MDBK), the non-toxic concentration of 5 µM OMF considerably reduced signs of cell death and increased cell proliferation. Furthermore, OMF significantly decreased the virus titer as well as the cytopathic effect and strongly inhibited the expression of bICP0, the major regulatory protein in the BoHV-1 lytic cycle. These findings were accompanied by a considerable up-regulation in the expression of the aryl hydrocarbon receptor (AhR), a multifunctional transcription factor also linked to the host’s response to a herpesvirus infection. Overall, our results suggest that by involving AhR, OMF shows potential against a BoHV-1 infection. Full article
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13 pages, 2347 KiB  
Article
Biosynthesis of 2-Heptanone, a Volatile Organic Compound with a Protective Role against Honey Bee Pathogens, by Hive Associated Bacteria
by Maria Ludovica Saccà, Giulia Bianchi and Roberto Lo Scalzo
Microorganisms 2021, 9(11), 2218; https://doi.org/10.3390/microorganisms9112218 - 26 Oct 2021
Cited by 4 | Viewed by 1907
Abstract
Beehives are populated by bacterial species with a protective role against honey bee pathogens thanks to the production of bioactive metabolites. These compounds are largely unexploited despite their high potential interest for pest management. This study evaluated the capability of bacterial species associated [...] Read more.
Beehives are populated by bacterial species with a protective role against honey bee pathogens thanks to the production of bioactive metabolites. These compounds are largely unexploited despite their high potential interest for pest management. This study evaluated the capability of bacterial species associated with honey bees to produce 2-heptanone, a volatile organic compound with anesthetic properties of the parasitic mite Varroa destructor. The production of this compound was quantified by SPME-GC-MS in a culture filtrate of nine bacterial strains isolated from the surface of honey bees, and the biosynthetic potential was evaluated in bacterial species associated with apiaries by searching for protein homologs putatively involved in its biosynthesis by using biocomputational tools. The findings pointed out that 2-heptanone was produced by Acetobacteraceae bacterium, Bacillus thuringiensis and Apilactobacillus kunkeei isolates in concentrations between 1.5 and 2.6 ng/mL and that its production was strain-specific. Putative methylketone synthase homologs were found in Bacillus, Gilliamella, Acetobacteraceae, Bartonella and Lactobacillaceae, and the protein sequence results were distributed in nine Sequence Similarity Network (SSN) clusters. These preliminary results support the hypothesis that 2-heptanone may act as a mediator of microbial relationships in hives and provide contributions to assess the role and biosynthetic potential of 2-heptanone in apiaries. Full article
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12 pages, 948 KiB  
Article
Ammonia Production by Streptomyces Symbionts of Acromyrmex Leaf-Cutting Ants Strongly Inhibits the Fungal Pathogen Escovopsis
by Basanta Dhodary and Dieter Spiteller
Microorganisms 2021, 9(8), 1622; https://doi.org/10.3390/microorganisms9081622 - 29 Jul 2021
Cited by 8 | Viewed by 2434
Abstract
Leaf-cutting ants live in mutualistic symbiosis with their garden fungus Leucoagaricus gongylophorus that can be attacked by the specialized pathogenic fungus Escovopsis. Actinomyces symbionts from Acromyrmex leaf-cutting ants contribute to protect L. gongylophorus against pathogens. The symbiont Streptomyces sp. Av25_4 exhibited strong [...] Read more.
Leaf-cutting ants live in mutualistic symbiosis with their garden fungus Leucoagaricus gongylophorus that can be attacked by the specialized pathogenic fungus Escovopsis. Actinomyces symbionts from Acromyrmex leaf-cutting ants contribute to protect L. gongylophorus against pathogens. The symbiont Streptomyces sp. Av25_4 exhibited strong activity against Escovopsis weberi in co-cultivation assays. Experiments physically separating E. weberi and Streptomyces sp. Av25_4 allowing only exchange of volatiles revealed that Streptomyces sp. Av25_4 produces a volatile antifungal. Volatile compounds from Streptomyces sp. Av25_4 were collected by closed loop stripping. Analysis by NMR revealed that Streptomyces sp. Av25_4 overproduces ammonia (up to 8 mM) which completely inhibited the growth of E. weberi due to its strong basic pH. Additionally, other symbionts from different Acromyrmex ants inhibited E. weberi by production of ammonia. The waste of ca. one third of Acomyrmex and Atta leaf-cutting ant colonies was strongly basic due to ammonia (up to ca. 8 mM) suggesting its role in nest hygiene. Not only complex and metabolically costly secondary metabolites, such as polyketides, but simple ammonia released by symbionts of leaf-cutting ants can contribute to control the growth of Escovopsis that is sensitive to ammonia in contrast to the garden fungus L. gongylophorus. Full article
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17 pages, 964 KiB  
Article
Characterisation of the Antibiotic Profile of Lysobacter capsici AZ78, an Effective Biological Control Agent of Plant Pathogenic Microorganisms
by Francesca Brescia, Anthi Vlassi, Ana Bejarano, Bernard Seidl, Martina Marchetti-Deschmann, Rainer Schuhmacher and Gerardo Puopolo
Microorganisms 2021, 9(6), 1320; https://doi.org/10.3390/microorganisms9061320 - 17 Jun 2021
Cited by 16 | Viewed by 3400
Abstract
Determining the mode of action of microbial biocontrol agents plays a key role in their development and registration as commercial biopesticides. The biocontrol rhizobacterium Lysobacter capsici AZ78 (AZ78) is able to inhibit a vast array of plant pathogenic oomycetes and Gram-positive bacteria due [...] Read more.
Determining the mode of action of microbial biocontrol agents plays a key role in their development and registration as commercial biopesticides. The biocontrol rhizobacterium Lysobacter capsici AZ78 (AZ78) is able to inhibit a vast array of plant pathogenic oomycetes and Gram-positive bacteria due to the release of antimicrobial secondary metabolites. A combination of MALDI-qTOF-MSI and UHPLC-HRMS/M was applied to finely dissect the AZ78 metabolome and identify the main secondary metabolites involved in the inhibition of plant pathogenic microorganisms. Under nutritionally limited conditions, MALDI-qTOF-MSI revealed that AZ78 is able to release a relevant number of antimicrobial secondary metabolites belonging to the families of 2,5-diketopiperazines, cyclic lipodepsipeptides, macrolactones and macrolides. In vitro tests confirmed the presence of secondary metabolites toxic against Pythium ultimum and Rhodococcus fascians in AZ78 cell-free extracts. Subsequently, UHPLC-HRMS/MS was used to confirm the results achieved with MALDI-qTOF-MSI and investigate for further putative antimicrobial secondary metabolites known to be produced by Lysobacter spp. This technique confirmed the presence of several 2,5-diketopiperazines in AZ78 cell-free extracts and provided the first evidence of the production of the cyclic depsipeptide WAP-8294A2 in a member of L. capsici species. Moreover, UHPLC-HRMS/MS confirmed the presence of dihydromaltophilin/Heat Stable Antifungal Factor (HSAF) in AZ78 cell-free extracts. Due to the production of HSAF by AZ78, cell-free supernatants were effective in controlling Plasmopara viticola on grapevine leaf disks after exposure to high temperatures. Overall, our work determined the main secondary metabolites involved in the biocontrol activity of AZ78 against plant pathogenic oomycetes and Gram-positive bacteria. These results might be useful for the future development of this bacterial strain as the active ingredient of a microbial biopesticide that might contribute to a reduction in the chemical input in agriculture. Full article
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Review

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20 pages, 424 KiB  
Review
Rhizosphere Microbial Communities and Heavy Metals
by Anna Barra Caracciolo and Valentina Terenzi
Microorganisms 2021, 9(7), 1462; https://doi.org/10.3390/microorganisms9071462 - 08 Jul 2021
Cited by 92 | Viewed by 6288
Abstract
The rhizosphere is a microhabitat where there is an intense chemical dialogue between plants and microorganisms. The two coexist and develop synergistic actions, which can promote plants’ functions and productivity, but also their capacity to respond to stress conditions, including heavy metal (HM) [...] Read more.
The rhizosphere is a microhabitat where there is an intense chemical dialogue between plants and microorganisms. The two coexist and develop synergistic actions, which can promote plants’ functions and productivity, but also their capacity to respond to stress conditions, including heavy metal (HM) contamination. If HMs are present in soils used for agriculture, there is a risk of metal uptake by edible plants with subsequent bioaccumulation in humans and animals and detrimental consequences for their health. Plant productivity can also be negatively affected. Many bacteria have defensive mechanisms for resisting heavy metals and, through various complex processes, can improve plant response to HM stress. Bacteria-plant synergic interactions in the rhizosphere, as a homeostatic ecosystem response to HM disturbance, are common in soil. However, this is hard to achieve in agroecosystems managed with traditional practices, because concentrating on maximizing crop yield does not make it possible to establish rhizosphere interactions. Improving knowledge of the complex interactions mediated by plant exudates and secondary metabolites can lead to nature-based solutions for plant health in HM contaminated soils. This paper reports the main ecotoxicological effects of HMs and the various compounds (including several secondary metabolites) produced by plant-microorganism holobionts for removing, immobilizing and containing toxic elements. Full article
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