Occurrence of Fungi and Fungal Toxins in Fish Feed During Storage

The Autophagy-Related Protein ATG8 Orchestrates Asexual Development and AFB1 Biosynthesis in Aspergillus flavus

Autophagy, a conserved cellular recycling process, plays a crucial role in maintaining homeostasis under stress conditions. It also regulates the development and virulence of numerous filamentous fungi. In this study, we investigated the specific function of ATG8, a reliable autophagic marker, in the opportunistic pathogen Aspergillus flavus. To investigate the role of atg8 in A. flavus, the deletion and complemented mutants of atg8 were generated according to the homologous recombination principle. Deletion of atg8 showed a significant decrease in conidiation, spore germination, and sclerotia formation compared to the WT and atg8C strains. Additionally, aflatoxin production was found severely impaired in the ∆atg8 mutant. The stress assays demonstrated that ATG8 was important for A. flavus response to oxidative stress. The fluorescence microscopy showed increased levels of reactive oxygen species in the ∆atg8 mutant cells, and the transcriptional result also indicated that genes related to the antioxidant system were significantly reduced in the ∆atg8 mutant. We further found that ATG8 participated in regulating the pathogenicity of A. flavus on crop seeds. These results revealed the biological role of ATG8 in A. flavus, which might provide a potential target for the control of A. flavus and AFB1 biosynthesis.

Unveiling the emerging role of curcumin to alleviate ochratoxin A-induced muscle toxicity in grass carp (Ctenopharyngodon idella): in vitro and in vivo studies

BACKGROUND

Ochratoxin A (OTA), a globally abundant and extremely hazardous pollutant, is a significant source of contamination in aquafeeds and is responsible for severe food pollution. The developmental toxicity of OTA and the potential relieving strategy of natural products remain unclear. This study screened the substance curcumin (Cur), which had the best effect in alleviating OTA inhibition of myoblast proliferation, from 96 natural products and investigated its effect and mechanism in reducing OTA myotoxicity in vivo and in vitro.

METHODS

A total of 720 healthy juvenile grass carp, with an initial average body weight of 11.06 ± 0.05 g, were randomly assigned into 4 groups: the control group (without OTA and Cur), 1.2 mg/kg OTA group, 400 mg/kg Cur group, and 1.2 mg/kg OTA + 400 mg/kg Cur group. Each treatment consisted of 3 replicates (180 fish) for 60 d.

RESULTS

Firstly, we cultured, purified, and identified myoblasts using the tissue block culture method. Through preliminary screening and re-screening of 96 substances, we examined cell proliferation-related indicators such as cell viability and ultimately found that Cur had the best effect. Secondly, Cur could alleviate OTA-inhibited myoblast differentiation and myofibrillar development-related proteins (MyoG and MYHC) in vivo and in vitro and improve the growth performance of grass carp. Then, Cur could also promote the expression of OTA-inhibited protein synthesis-related proteins (S6K1 and TOR), which was related to the activation of the AKT/TOR signaling pathway. Finally, Cur could downregulate the expression of OTA-enhanced protein degradation-related genes (murf1, foxo3a, and ub), which was related to the inhibition of the FoxO3a signaling pathway.

CONCLUSIONS

In summary, our data demonstrated the effectiveness of Cur in alleviating OTA myotoxicity in vivo and in vitro. This study confirms the rapidity, feasibility, and effectiveness of establishing a natural product screening method targeting myoblasts to alleviate fungal toxin toxicity.

Ochratoxin A induces locomotor impairment and oxidative imbalance in adult zebrafish

Ochratoxin A (OTA) is a mycotoxin produced by species of filamentous fungi widely found as a contaminant in food and with high toxic potential. Studies have shown that this toxin causes kidney and liver damage; however, data on the central nervous system effects of exposure to OTA are still scarce. Thus, this study aimed to investigate the effects of exposure to OTA on behavioral and neurochemical parameters in adult zebrafish. The animals were treated with different doses of OTA (1.38, 2.77, and 5.53 mg/kg) with intraperitoneal injections and submitted to behavioral evaluations in the open tank and social interaction tests. Subsequently, they were euthanized, and the brains were used to assess markers associated with oxidative status. In the open tank test, OTA altered distance traveled, absolute turn angle, mean speed, and freezing time. However, no significant effects were observed in the social interaction test. Moreover, OTA also increased glutathione peroxidase (GPx), glutathione-S-transferase (GST), and glutathione reductase (GR) levels and decreased non-protein thiols (NPSH) levels in the zebrafish brain. This study showed that OTA can affect behavior and neurochemical levels in zebrafish.

Lactobacillus plantarum and Deoxynivalenol Detoxification: A Concise Review

ABSTRACT

Mycotoxins are toxic secondary fungal metabolites that contaminate feeds, and their levels remain stable during feed processing. The economic impact of mycotoxins on animal production happens mainly due to losses related to direct effects on animal health and trade losses related to grain rejection. Deoxynivalenol (DON) is a trichothecene mycotoxin that has contaminated approximately 60% of the grains worldwide. Ingestion of DON induces many toxic effects on human and animal health. Detoxification strategies to decrease DON levels in food and feeds include physical and chemical methods; however, they are not very effective when incorporated into the industrial production process. A valuable alternative to achieve this aim is the use of lactic acid bacteria. These bacteria can control fungal growth and thus overcome DON production or can detoxify the mycotoxin through adsorption and biotransformation. Some Lactobacillus spp. strains, such as Lactobacillus plantarum, have demonstrated preventive effects against DON toxicity in poultry and swine. This beneficial effect is associated with a binding capacity of lactic acid bacteria cell wall peptidoglycan with mycotoxins. Moreover, several antifungal compounds have been isolated from L. plantarum supernatants, including lactic, acetic, caproic, phenyl lactic, 3-hydroxylated fatty, and cyclic dipeptide acids. Biotransformation of DON by L. plantarum into other products is also hypothesized, but the mechanism remains unknown. In this concise review, we highlight the use of L. plantarum as an alternative approach to reduce DON levels and toxicity. Although the action mechanism of L. plantarum is still not fully understood, these bacteria are a safe, efficient, and low-cost strategy to reduce economic losses from mycotoxin contamination cases.

HIGHLIGHTS

Exploitation of the Antibacterial Properties of Photoactivated Curcumin as ‘Green’ Tool for Food Preservation

In the search for non-chemical and green methods to counteract the bacterial contamination of foods, the use of natural substances with antimicrobial properties and light irradiation at proper light waves has been extensively investigated. In particular, the combination of both techniques, called photodynamic inactivation (PDI), is based on the fact that some natural substances act as photosensitizers, i.e., produce bioactive effects under irradiation. Notably, curcumin is a potent natural antibacterial and effective photosensitizer that is able to induce photodynamic activation in the visible light range (specifically for blue light). Some practical applications have been investigated with particular reference to food preservation from bacterial contaminants.

Dysfunction of FadA-cAMP signalling decreases Aspergillus flavus resistance to antimicrobial natural preservative Perillaldehyde and AFB1 biosynthesis

Aspergillus flavus is an opportunistic fungal pathogen that colonizes agriculture crops with aflatoxin contamination. We found that Perillaldehyde (PAE) effectively inhibited A. flavus viability and aflatoxin production by inducing excess reactive oxygen species (ROS). Transcriptome analysis indicated that the Gα protein FadA was significantly induced by PAE. Functional characterization of FadA showed it is important for asexual development and aflatoxin biosynthesis by regulation of cAMP-PKA signalling. The ΔfadA mutant was more sensitive to PAE, while ΔpdeL and ΔpdeH mutants can tolerate excess PAE compared to wild-type A. flavus. Further RNA-sequence analysis showed that fadA was important for expression of genes involved in oxidation-reduction and cellular metabolism. The flow cytometry and fluorescence microscopy demonstrated that ΔfadA accumulated more concentration of ROS in cells, and the transcriptome data indicated that genes involved in ROS scavenging were downregulated in ΔfadA mutant. We further found that FadA participated in regulating response to extracellular environmental stresses by increasing phosphorylation levels of MAPK Kinase Slt2 and Hog1. Overall, our results indicated that FadA signalling engages in mycotoxin production and A. flavus resistance to antimicrobial PAE, which provide valuable information for controlling this fungus and AF biosynthesis in pre- and postharvest of agricultural crops.

Fungi population metabolomics and molecular network study reveal novel biomarkers for early detection of aflatoxigenic Aspergillus species

Mycotoxins threaten global food safety, public health and cause huge socioeconomic losses. Early detection is an effective preventive strategy, yet efficient biomarkers for early detection of aflatoxigenic Aspergillus species are lacking. Here, we proposed to use untargeted metabolomics and machine learning to mine biomarkers of aflatoxigenic Aspergillus species. We systematically delineated metabolic differences across 568 extensive field sampling A. flavus and performed biomarker analysis. Versicolorin B, 11-hydroxy-O-methylsterigmatocystin et.al metabolites shown a high correlation (from 0.71 to 0.95) with strains aflatoxin-producing capacity. Molecular networking analysis deciphered the connection of aflatoxins and biomarkers as well as potential emerging mycotoxins. We then developed a model using the biomarkers as variables to discern aflatoxigenic Aspergillus species with 97.8% accuracy. A validation dataset and metabolome from other 16 fungal isolates confirmed the robustness and specificity of these biomarkers. We further demonstrated the solution feasibility in agricultural products by early detection of biomarkers, which predicted aflatoxin contamination risk 35-47 days in advance. A developed operable decision rule by the XGBoost algorithm help regulators to intuitively assess the risk prioritization with 87.2% accuracy. Our research provides novel insights into global food safety risk assessment which will be crucial for early prevention and control of mycotoxins.

Increasing disease burden and use of drugs and chemicals in Bangladesh shrimp aquaculture: A potential menace to human health

Using structured surveys in 2008 and 2016, change in disease burden and use of chemical treatments in Bangladesh shrimp farm management was examined. Overall, disease burden had increased in all farms and was more polarized, with a fewer number of individual infectious diseases responsible for most disease in ponds. Farmers also reported physical deformities, nutritional deficiencies, and unknown diseases further indicating poor health of their stock. To combat the threat, more chemical treatments were used (5.2 treatments per farm in 2008 versus 28.8 in 2016), resulting in an average increase of 424% in the number of active substances entering shrimp ponds. Although there was a modest reduction in the use of antimicrobials, shrimp was being exposed to a wider range of chemicals during rearing. The subsequent concern for the environment, animal and human health demands further research to identify potential risks from residues of chemical products.

The Occurrence of Mycotoxins in Raw Materials and Fish Feeds in Europe and the Potential Effects of Deoxynivalenol (DON) on the Health and Growth of Farmed Fish Species-A Review

The first part of this study evaluates the occurrence of mycotoxin patterns in feedstuffs and fish feeds. Results were extrapolated from a large data pool derived from wheat (n = 857), corn (n = 725), soybean meal (n = 139) and fish feed (n = 44) samples in European countries and based on sample analyses by liquid chromatography/tandem mass spectrometry (LC-MS/MS) in the period between 2012-2019. Deoxynivalenol (DON) was readily present in corn (in 47% of the samples) > wheat (41%) > soybean meal (11%), and in aquafeeds (48%). Co-occurrence of mycotoxins was frequently observed in feedstuffs and aquafeed samples. For example, in corn, multi-mycotoxin occurrence was investigated by Spearman's correlations and odd ratios, and both showed co-occurrence of DON with its acetylated forms (3-AcDON, 15-AcDON) as well as with zearalenone (ZEN). The second part of this study summarizes the existing knowledge on the effects of DON on farmed fish species and evaluates the risk of DON exposure in fish, based on data from in vivo studies. A meta-analytical approach aimed to estimate to which extent DON affects feed intake and growth performance in fish. Corn was identified as the ingredient with the highest risk of contamination with DON and its acetylated forms, which often cannot be detected by commonly used rapid detection methods in feed mills. Periodical state-of-the-art mycotoxin analyses are essential to detect the full spectrum of mycotoxins in fish feeds aimed to prevent detrimental effects on farmed fish and subsequent economic losses for fish farmers. Because levels below the stated regulatory limits can reduce feed intake and growth performance, our results show that the risk of DON contamination is underestimated in the aquaculture industry.