Natural Variation and the Role of Zn2Cys6 Transcription Factors SdrA, WarA and WarB in Sorbic Acid Resistance of Aspergillus niger

Abstract

Weak acids, such as sorbic acid, are used as chemical food preservatives by the industry. Fungi overcome this weak-acid stress by inducing cellular responses mediated by transcription factors. In our research, a large-scale sorbic acid resistance screening was performed on 100 A. niger sensu stricto strains isolated from various sources to study strain variability in sorbic acid resistance. The minimal inhibitory concentration of undissociated (MICu) sorbic acid at pH = 4 in the MEB of the A. niger strains varies between 4.0 mM and 7.0 mM, with the average out of 100 strains being 4.8 ± 0.8 mM, when scored after 28 days. MICu values were roughly 1 mM lower when tested in commercial ice tea. Genome sequencing of the most sorbic-acid-sensitive strain among the isolates revealed a premature stop codon inside the sorbic acid response regulator encoding gene sdrA. Repairing this missense mutation increased the sorbic acid resistance, showing that the sorbic-acid-sensitive phenotype of this strain is caused by the loss of SdrA function. To identify additional transcription factors involved in weak-acid resistance, a transcription factor knock-out library consisting of 240 A. niger deletion strains was screened. The screen identified a novel transcription factor, WarB, which contributes to the resistance against a broad range of weak acids, including sorbic acid. The roles of SdrA, WarA and WarB in weak-acid resistance, including sorbic acid, were compared by creating single, double and the triple knock-out strains. All three transcription factors were found to have an additive effect on the sorbic acid stress response.

Utilization of ferulic acid in Aspergillus niger requires the transcription factor FarA and a newly identified Far-like protein (FarD) that lacks the canonical Zn(II)2Cys6 domain

“…Only a few transcription factors that are involved in regulation of genes encoding the enzymes involved the degradation of aromatics have been identified. These include the Zn(II) 2 Cys 6 transcription factor SdrA which is required for the metabolism of cinnamic acid and sorbic acid ( Plumridge et al., 2010 ; Lubbers et al., 2019b , Seekles et al., 2022 ) and the TanR Zn(II) 2 Cys 6 transcription factor required for the degradation of tannin into gallic acid and subsequent metabolism of gallic acid ( Arentshorst et al., 2021 ). Here we show that deletion of FarA, a well described transcription factor required for the induction of genes involved in peroxisomal degradation of fatty acids ( Hynes et al., 2006 ; Hynes et al., 2008 ), is also required for the metabolism of hydroxycinnamic acids, including ferulic acid, p-coumaric acid and caffeic acid.…”

Antimicrobial activity of microencapsulated nisin with ascorbic acid and ethylenediaminetetraacetic acid prepared using double emulsion and freeze-drying technique against Salmonella Enteritidis ATCC 13076 in culture broth and minced fish

“…When the pH of the solution lower than the pKa of ascorbic acid (4.10), the proportion of undissociated form increases (Bevilacqua et al, 2023). Only its undissociated form is able to pass across the plasma membrane into the cytoplasm, resulting in acidification (Seekles et al, 2022). In the current study, the pH values of MHB with only ascorbic acid, N-A, A-E or N-A-E mixtures were 5.37, 5.38, 5.40 and 5.42, respectively, (data not shown), which were higher than the pKa value of ascorbic acid.…”

CRISPR/Cas9-Based Genome Editing and Its Application in Aspergillus Species

“…In addition, the well-established RNP-based CRISPR/Cas9 system has been successfully used in A. niger genetic engineering, and significantly improved the succinic acid production by disrupting and overexpressing multiple relevant genes in the engineered strain [ 11 ]. Recently, with the improvement of CRISPR/Cas9-based genome editing strategies, an increasing number of studies on gene function and metabolic regulation have been completed in A. niger [ 84 , 85 ].…”