Determination of two potential toxicity metabolites derived from the disruption of the pksCT gene in Monascus aurantiacus Li As3.4384

Putative C2H2 Transcription Factor AflZKS3 Regulates Aflatoxin and Pathogenicity in Aspergillus flavus

Aflatoxin is a carcinogenic secondary metabolite that poses a serious threat to human and animal health. Some C₂H₂ transcription factors are associated with fungal growth and secondary metabolic regulation. In this study, we characterized the role of AflZKS3, a putative C₂H₂ transcription factor based on genome annotation, in the growth and aflatoxin biosynthesis of A. flavus and explored its possible mechanisms of action. Surprisingly, the protein was found to be located in the cytoplasm, and gene deletion in A. flavus resulted in defective growth and conidia formation, as well as increased sensitivity to the fluorescent brightener Calcofluor white, Congo red, NaCl, and sorbitol stress. Notably, the biosynthesis of aflatoxin B₁ was completely inhibited in the ΔAflZKS3 deletion strain, and its ability to infect peanut and corn seeds was also reduced. RNA sequencing showed that differentially expressed genes in the ΔAflZKS3 strain compared with the control and complementation strains were mainly associated with growth, aflatoxin biosynthesis, and oxidative stress. Thus, AflZKS3 likely contributes to growth, cell development, and aflatoxin synthesis in A. flavus. These findings lay the foundation for a deeper understanding of the roles of C₂H₂ transcription factors in A. flavus and provide a potential biocontrol target for preventing aflatoxin contamination.

The Effect of Blue Light on the Production of Citrinin in Monascus purpureus M9 by Regulating the mraox Gene through lncRNA AOANCR

Blue light, as an important environmental factor, can regulate the production of various secondary metabolites of Monascus purpureus M9, including mycotoxin-citrinin, pigments, and monacolin K. The analysis of citrinin in Monascus M9 exposed to blue light for 0 min./d, 15 min./d, and 60 min./d showed that 15 min./d of blue light illumination could significantly increase citrinin production, while 60 min./d of blue light illumination decreased citrinin production. Analysis of long non-coding RNA (LncRNA) was performed on the transcripts of Monascus M9 under three culture conditions, and this analysis identified an lncRNA named AOANCR that can negatively regulate the mraox gene. Fermentation studies suggested that alternate respiratory pathways could be among the pathways that are involved in the regulation of the synthesis of citrinin by environmental factors. Aminophylline and citric acid were added to the culture medium to simulate the process of generating cyclic adenosine monophosphate (cAMP) in cells under illumination conditions. The results of the fermentation showed that aminophylline and citric acid could increase the expression of the mraox gene, decrease the expression of lncRNA AOANCR, and reduce the yield of citrinin. This result also indicates a reverse regulation relationship between lncRNA AOANCR and the mraox gene. A blue light signal might regulate the mraox gene at least partially through lncRNA AOANCR, thereby regulating citrinin production. Citrinin has severe nephrotoxicity in mammals, and it is important to control the residual amout of citrinin in red yeast products during fermentation. LncRNA AOANCR and mraox can potentially be used as new targets for the control of citrinin production.

Soybean isoflavones reduce citrinin production by Monascus aurantiacus Li AS3.4384 in liquid state fermentation using different media

BACKGROUND

Monascus, a filamentous fungus, produces many bioactive substances. However, in the process of fermentation, Monascus also produces the mycotoxin citrinin. Owing to the presence of citrinin, the safety of Monascus products has been questioned and their wide application limited. Using soybean isoflavones (SI) as exogenous additives, alterations in citrinin production by Monascus aurantiacus Li AS3.4384 (MALA) in different media used for liquid state fermentation were investigated.

RESULTS

Results showed that the citrinin concentration was 95.98% lower than that of the control group after 16-days fermentation when 20.0 g L-1 SI were added to rice powder and inorganic salt medium. Citrinin production was reduced by 97.24% after 12-days fermentation with 10.0 g L-1 SI in starch inorganic salt medium; 82.52% after 20-days fermentation with 20.0 g L-1 SI in starch peptone medium with high starch content; 45.07% after 14-days fermentation with 5.0 g L-1 SI in starch peptone medium with low starch content; and 82.21% after 14-days fermentation with 20.0 g L-1 SI in yeast extract sucrose medium.

CONCLUSION

The developed method of removing citrinin is simple, safe, and effective, and it can be applied to reduce the citrinin content of Monascus products. © 2019 Society of Chemical Industry.