The Solvent Dimethyl Sulfoxide Affects Physiology, Transcriptome and Secondary Metabolism of Aspergillus flavus

Abstract

Dimethyl sulfoxide (DSMO) is a simple molecule widely used because of its great solvating ability, but this solvent also has little-known biological effects, especially on fungi. Aspergillus flavus is a notorious pathogenic fungus which may contaminate a large variety of crops worldwide by producing aflatoxins, endangering at the same time food safety and international trade. The aim of this study was to characterize the effect of DMSO on A. flavus including developmental parameters such as germination and sporulation, as well as its transcriptome profile using high-throughput RNA-sequencing assay and its impact on secondary metabolism (SM). After DMSO exposure, A. flavus displayed depigmented conidia in a dose-dependent manner. The four-day exposition of cultures to two doses of DMSO, chosen on the basis of depigmentation intensity (35 mM “low” and 282 mM “high”), led to no significant impact on fungal growth, germination or sporulation. However, transcriptomic data analysis showed that 4891 genes were differentially regulated in response to DMSO (46% of studied transcripts). A total of 4650 genes were specifically regulated in response to the highest dose of DMSO, while only 19 genes were modulated upon exposure to the lowest dose. Secondary metabolites clusters genes were widely affected by the DMSO, with 91% of clusters impacted at the highest dose. Among these, aflatoxins, cyclopiazonic acid and ustiloxin B clusters were totally under-expressed. The genes belonging to the AFB1 cluster were the most negatively modulated ones, the two doses leading to 63% and 100% inhibition of the AFB1 production, respectively. The SM analysis also showed the disappearance of ustiloxin B and a 10-fold reduction of cyclopiazonic acid level when A. flavus was treated by the higher DMSO dose. In conclusion, the present study showed that DMSO impacted widely A. flavus’ transcriptome, including secondary metabolism gene clusters with the aflatoxins at the head of down-regulated ones. The solvent also inhibits conidial pigmentation, which could illustrate common regulatory mechanisms between aflatoxins and fungal pigment pathways. Because of its effect on major metabolites synthesis, DMSO should not be used as solvent especially in studies testing anti-aflatoxinogenic compounds.

Effect of Streptomyces roseolus Cell-Free Supernatants on the Fungal Development, Transcriptome, and Aflatoxin B1 Production of Aspergillus flavus

“…The global transcriptomic analysis conducted in the present study demonstrated that the reduction in AFB1 concentration in A. flavus is consistent with a drastic downregulation of the entire aflatoxins’ gene cluster ( Figure 8 ) as already demonstrated in several studies [ 23 , 54 , 60 , 67 , 68 , 69 ]. Indeed, genetic regulation of aflatoxin biosynthesis is widely described, involving aflR and aflS .…”

“…In the same way, among the twelve genes involved in the aspergillic acid cluster, seven were significantly downregulated ( Figure 10 ), notably asaB , coding for a GA4 desaturase family protein. This gene was also downregulated when A. flavus was grown with dimethyl sulfoxide (DMSO) at a concentration of 281.6 mM [ 69 ]. Nevertheless, the LC-HRMS analysis revealed that the relative abundance of aspergillic acid was nine-fold higher in A. flavus exposed to CFS4 than under control conditions, suggesting a more complex mechanism of regulation.…”

“…The metabolites were identified based on their MS/MS spectrum, MS/MS fragmentation pattern, and retention times, compared with those of the standard compounds or data from AntiBase 2012 or the literature [ 69 , 89 ].…”

Experimental verification of strain-dependent relationship between mycovirus and its fungal host

“…From the DEG data, over- or underrepresented FunCat categories were explored in each set (See Table S3 ), which showed that metabolism was overrepresented in all strains. Then, we inspected gene expression levels in 59 SM clusters that have been estimated in A. flavus 29 , 30 , 31 , 32 (See Table S4 ). In the 8 pairs of virus-infected and -free isolates, 26 to 37 SM clusters were not expressed regardless of virus infection.…”