Zearalenone detoxification by zearalenone hydrolase is important for the antagonistic ability of Clonostachys rosea against mycotoxigenic Fusarium graminearum

Isolation and characterisation of enzymatic zearalenone hydrolysis reaction products

Zearalenone (ZEA) is an oestrogenic mycotoxin produced by several Fusarium species, and it frequently contaminates cereals used for food or animal feed. A ZEA-lactonase of Gliocladium roseum was previously described to hydrolyse ZEA to an unstable intermediate, which spontaneously decarboxylates to non-oestrogenic, decarboxylated hydrolysed ZEA (DHZEN). We expressed a codon-optimised version of the ZEA-lactonase (ZHD101) gene of G. roseum MA 918 with a secretion leader in Pichia pastoris and purified the recombinant enzyme from culture supernatant by His-tag mediated affinity chromatography. After incubation of the enzyme with ZEA, we detected the previously elusive primary reaction product hydrolysed ZEA (HZEN) by liquid chromatography tandem mass spectrometry, purified it by preparative high-performance liquid chromatography, and confirmed its postulated structure ((E)-2,4-dihydroxy-6-(10-hydroxy-6-oxo-1-undecen-1-yl)benzoic acid) by nuclear magnetic resonance techniques. Spontaneous decarboxylation to DHZEN ((E)-1-(3,5-dihydroxy-phenyl)-10-hydroxy-1-undecen-6-one), but not to a previously reported isomer, was observed. Biomass resuspensions of G. roseum strains MA 918 and the strains used for previous work, NBRC 7063 and ATCC 8684, all converted ZEA to HZEN, DHZEN, and further unknown metabolites. We studied partitioning of HZEN and DHZEN between aqueous phases and organic solvents, and found that HZEN did not partition into chloroform as extraction solvent, under the conditions used by previous authors. In contrast, extraction with ethyl acetate at pH 2.0 was suitable for simultaneous extraction of HZEN and DHZEN. The detection of HZEN and its availability as an analytical standard may assist further work towards possible application of ZEA-lactonase (e.g. determining kinetic parameters) for detoxification of ZEA.

Relationship between mycoparasites lifestyles and biocontrol behaviors against Fusarium spp. and mycotoxins production

Global food security research is seeking eco-friendly solutions to control mycotoxins in grain infected by fungi (molds). In particular, mycotoxigenic Fusarium spp. outbreak is a chronic threat for cereal grain production, human, and animal health. In this review paper, we discuss up-to-date biological control strategies in applying mycoparasites as biological control agents (BCA) to prevent plant diseases in crops and mycotoxins in grain, food, and feed. The aim is to increase food safety and to minimize economic losses due to the reduced grain yield and quality. However, recent papers indicate that the study of the BCA specialists with biotrophic lifestyle lags behind our understanding of the BCA generalists with necrotrophic lifestyle. We examine critical behavioral traits of the two BCA groups of mycoparasites. The goal is to highlight their major characteristics in the context of future research towards an efficient biocontrol strategy against mycotoxin-producing Fusarium species. The emphasis is put on biocontrol of Fusarium graminearum, F. avenaceum, and F. culmorum causing Fusarium head blight (FHB) in cereals and their mycotoxins.

Biodegradation of zearalenone by Saccharomyces cerevisiae: Possible involvement of ZEN responsive proteins of the yeast

The mycotoxin zearalenone, also known as F-2 mycotoxin or RAL is a potent estrogenic metabolite produced by some Gibberella and Fusarium species. It is a common contaminant of cereal crops, livestock and poultry products. However, detoxification of zearalenone (ZEN) remains a challenge. Recently, biological approach for ZEN detoxification is being explored. In this study, we investigated the biodegradation of ZEN by using Saccharomyces cerevisiae and the possible mechanisms involved. The findings revealed that, after 48h of incubation of S. cerevisiae in combination with ZEN, the ZEN was completely degraded by S. cerevisiae. On the contrary, heat-killed cells and cell-free culture filtrates of S. cerevisiae could not degrade ZEN. Furthermore, addition of cycloheximide to S. cerevisiae combined with ZEN at time 0h prevented ZEN degradation, while addition of cycloheximide at 12h significantly slowed down degradation. The results also indicated cellular proteomics of S. cerevisiae. Several differential proteins were identified, most of which were related to basic metabolism.

BIOLOGICAL SIGNIFICANCE

The findings revealed that, after 48h of incubating ZEN together with S. cerevisiae, ZEN was completely degraded by S. cerevisiae. The mechanisms involved in the degradation of ZEN by S. cerevisiae may be the production of associated intracellular and extracellular enzymes, which have the ability to degrade ZEN. In addition, there were some functional proteins produced by S. cerevisiae, indicating that the basic metabolism of S. cerevisiae was improved when ZEN was added. This novel discovery by the authors, will greatly contribute to the field of biodegradation of mycotoxin by antagonists. The authors also believed this innovation will open the grounds for further research and improvement of S. cerevisiae in the field of biodegradation.

Isolation of Secondary Metabolites from the Soil-Derived Fungus Clonostachys rosea YRS-06, a Biological Control Agent, and Evaluation of Antibacterial Activity

The fungus Clonostachys rosea is widely distributed all over the world. The destructive force of this fungus, as a biological control agent, is very strong to lots of plant pathogenic fungi. As part of the ongoing search for antibiotics from fungi obtained from soil samples, the secondary metabolites of C. rosea YRS-06 were investigated. Through efficient bioassay-guided isolation, three new bisorbicillinoids possessing open-ended cage structures, tetrahydrotrichodimer ether (1) and dihydrotrichodimer ether A and B (2 and 3), and 12 known compounds were obtained. Their structures were determined via extensive NMR, HR-ESI-MS, and CD spectroscopic analyses and X-ray diffraction data. Compounds 1-3 are rare bisorbicillinoids with a γ-pyrone moiety. The biological properties of 1-15 were evaluated against six different Gram-positive and Gram-negative bacteria. Bisorbicillinoids, 2-5, and TMC-151 C and E, 14 and 15, showed potent antibacterial activity.

Dual effects of Metarhizium spp. and Clonostachys rosea against an insect and a seed-borne pathogen in wheat

BACKGROUND

Crops are often prone to both insect herbivory and disease, which necessitate multiple control measures. Ideally, an efficacious biological control agent must adequately control the target organism and not be inhibited by other biological control agents when applied simultaneously. Wheat seeds infected with the plant pathogen Fusarium culmorum were treated with Metarhizium brunneum or M. flavoviride and Clonostachys rosea individually and in combination, with the expectation to control both root-feeding insects and the pathogen. Emerging roots were evaluated for disease and then placed with Tenebrio molitor larvae, which were monitored for infection.

RESULTS

Plant disease symptoms were nearly absent for seeds treated with C. rosea, both individually and in combination with Metarhizium spp. Furthermore, roots grown from seeds treated with Metarhizium spp. caused significant levels of fungal infection in larvae when used individually or combined with C. rosea. However, cotreated seeds showed reduced virulence towards T. molitor when compared with treatments using Metarhizium spp. only.

CONCLUSIONS

This study clearly shows that seed treatments with both the entomopathogenic fungus M. brunneum and the mycoparasitic fungus C. rosea can protect plant roots from insects and disease. The dual-treatment approach to biological control presented here is consistent with the ideals of IPM strategies.

Identification of mycoparasitism-related genes in Clonostachys rosea 67-1 active against Sclerotinia sclerotiorum

Clonostachys rosea is a mycoparasite that has shown great potential in controlling various plant fungal pathogens. In order to find mycoparasitism-related genes in C. rosea, the transcriptome of the efficient isolate 67-1 in association with sclerotia of Sclerotinia sclerotiorum was sequenced and analysed. The results identified 26,351 unigenes with a mean length of 1,102 nucleotides, among which 18,525 were annotated in one or more databases of NR, KEGG, Swiss-Prot, GO and COG. Differentially expressed genes at 8 h, 24 h and 48 h after sclerotial induction were analysed, and 6,890 unigenes were upregulated compared with the control without sclerotia. 713, 1,008 and 1,929 genes were specifically upregulated expressed, while 1,646, 283 and 529 genes were specifically downregulated, respectively. Gene ontology terms analysis indicated that these genes were mainly involved in metabolism of biological process, catalysis of molecular function and cellular component. The expression levels of 12 genes that were upregulated after encountering with S. sclerotiorum were monitored using real-time PCR. The results indicated that the quantitative detection was consistent with the transcriptome analysis. The study provides transcriptional gene expression information on C. rosea parasitizing S. sclerotiorum and forms the basis for further investigation of mycoparasitism-related genes of C. rosea.

The ABC transporter ABCG29 is involved in H2O2 tolerance and biocontrol traits in the fungus Clonostachys rosea

For successful biocontrol interactions, biological control organisms must tolerate toxic metabolites produced by themselves or plant pathogens during mycoparasitic/antagonistic interactions, by host plant during colonization of the plant, and xenobiotics present in the environment. ATP-binding cassette (ABC) transporters can play a significant role in tolerance of toxic compounds by mediating active transport across the cellular membrane. This paper reports on functional characterization of an ABC transporter ABCG29 in the biocontrol fungus Clonostachys rosea strain IK726. Gene expression analysis showed induced expression of abcG29 during exposure to the Fusarium spp. mycotoxin zearalenone (ZEA) and the fungicides Cantus, Chipco Green and Apron. Expression of abcG29 in C. rosea was significantly higher during C. rosea-C. rosea (Cr-Cr) interaction or in exposure to C. rosea culture filtrate for 2 h, compared to interaction with Fusarium graminearum or 2 h exposure to F. graminearum culture filtrate. In contrast with gene expression data, ΔabcG29 strains did not display reduced tolerance towards ZEA, fungicides or chemical agents known for inducing oxidative, cell wall or osmotic stress, compared to C. rosea WT. The exception was a significant reduction in tolerance to H2O2 (10 mM) in ΔabcG29 strains when conidia were used as an inoculum. The antagonistic ability of ΔabcG29 strains towards F. graminearum, Fusarium oxysporum or Botrytis cinerea in dual plate assays were not different compared with WT. However, in biocontrol assays ΔabcG29 strains displayed reduced ability to protect Arabidopsis thaliana leaves from B. cinerea, and barley seedling from F. graminearum as measured by an A. thaliana detached leaf assay and a barley foot rot disease assay, respectively. These data show that the ABCG29 is dispensable for ZEA and fungicides tolerance, and antagonism but not H2O2 tolerance and biocontrol effects in C. rosea.

Draft Genome Sequence of Mycoparasite Clonostachys rosea Strain 67-1

Clonostachys rosea is a promising mycoparasite. In this study, we sequenced the draft genome of the highly effective strain 67-1 using the Illumina HiSeq 2500 sequencing platform. The genome is 55.4 Mb with a G+C content of 49.2% and provides a powerful resource for future studies on the molecular mechanisms underlying Clonostachys rosea's antagonism on fungal pathogens.

Selection of reliable reference genes for gene expression studies in Clonostachys rosea 67-1 under sclerotial induction

Reference genes are important to precisely quantify gene expression by real-time PCR. In order to identify stable and reliable expressed genes in mycoparasite Clonostachys rosea in different modes of nutrition, seven commonly used housekeeping genes, 18S rRNA, actin, β-tubulin, elongation factor 1, ubiquitin, ubiquitin-conjugating enzyme and glyceraldehyde-3-phosphate dehydrogenase, from the effective biocontrol isolate C. rosea 67-1 were tested for their expression under sclerotial induction and during vegetative growth on PDA medium. Analysis by three software programs showed that differences existed among the candidates. Elongation factor 1 was most stable; the M value in geNorm, SD value in Bestkeeper and stability value in Normfinder analysis were 0.405, 0.450 and 0.442, respectively, indicating that the gene elongation factor 1 could be used to normalize gene expression in C. rosea in both vegetative growth and parasitic process. By using elongation factor 1, the expression of a serine protease gene, sep, in different conditions was assessed, which was consistent with the transcriptomic data. This research provides an effective method to quantitate expression changes of target genes in C. rosea, and will assist in further investigation of parasitism-related genes of this fungus.

A perilipin gene from Clonostachys rosea f. Catenulata HL-1-1 is related to sclerotial parasitism

Clonostachys rosea f. catenulata is a promising biocontrol agent against many fungal plant pathogens. To identify mycoparasitism-related genes from C. rosea f. catenulata, a suppression subtractive hybridization (SSH) cDNA library of C. rosea f. catenulata HL-1-1 that parasitizes the sclerotia of S. sclerotiorum was constructed. 502 clones were sequenced randomly, and thereby 472 expressed sequence tags (ESTs) were identified. Forty-three unigenes were annotated and exhibited similarity to a wide diversity of genes. Quantitative real -time PCR showed that a perilipin-like protein encoding gene, Per3, was up-regulated by 6.6-fold over the control at 96 h under the induction of sclerotia. The full-length sequence of Per3 was obtained via 5' and 3' rapid identification of cDNA ends. Overexpression of Per3 in HL-1-1 significantly enhanced the parasitic ability on sclerotia. The results indicated that Per3 might be involved in the mycoparasitism of C. rosea f. catenulata HL-1-1. This is the first report of a perilipin as a potential biocontrol gene in mycoparasites. The study provides usefu l insights into the interaction between C. rosea f. catenulata and fungal plant pathogens.