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  • 1
    Online Resource
    Online Resource
    Mapping the structural requirements of inducers and substrates for decarboxylation of weak acid preservatives by the food spoilage mould Aspergillus niger
    Elsevier BV ; 2012
    In:  International Journal of Food Microbiology Vol. 157, No. 3 ( 2012-07), p. 375-383
    Details
    In: International Journal of Food Microbiology, Elsevier BV, Vol. 157, No. 3 ( 2012-07), p. 375-383
    Type of Medium: Online Resource
    ISSN: 0168-1605
    URL: Article
    DOI: 10.1016/j.ijfoodmicro.2012.06.007
    Language: English
    Publisher: Elsevier BV
    Publication Date: 2012
    detail.hit.zdb_id: 2013748-5
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  • 2
    Online Resource
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    Weak Acid Resistance A (WarA), a Novel Transcription Factor Required for Regulation of Weak-Acid Resistance and Spore-Spore Heterogeneity in Aspergillus niger
    American Society for Microbiology ; 2020
    In:  mSphere Vol. 5, No. 1 ( 2020-02-26)
    Details
    In: mSphere, American Society for Microbiology, Vol. 5, No. 1 ( 2020-02-26)
    Abstract: Propionic, sorbic, and benzoic acids are organic weak acids that are widely used as food preservatives, where they play a critical role in preventing microbial growth. In this study, we uncovered new mechanisms of weak-acid resistance in molds. By screening a library of 401 transcription factor deletion strains in Aspergillus fumigatus for sorbic acid hypersensitivity, a previously uncharacterized transcription factor was identified and named weak acid resistance A (WarA). The orthologous gene in the spoilage mold Aspergillus niger was identified and deleted. WarA was required for resistance to a range of weak acids, including sorbic, propionic, and benzoic acids. A transcriptomic analysis was performed to characterize genes regulated by WarA during sorbic acid treatment in A. niger . Several genes were significantly upregulated in the wild type compared with a Δ warA mutant, including genes encoding putative weak-acid detoxification enzymes and transporter proteins. Among these was An14g03570, a putative ABC-type transporter which we found to be required for weak-acid resistance in A. niger . We also show that An14g03570 is a functional homologue of the Saccharomyces cerevisiae protein Pdr12p and we therefore name it PdrA. Last, resistance to sorbic acid was found to be highly heterogeneous within genetically uniform populations of ungerminated A. niger conidia, and we demonstrate that pdrA is a determinant of this heteroresistance. This study has identified novel mechanisms of weak-acid resistance in A. niger which could help inform and improve future food spoilage prevention strategies. IMPORTANCE Weak acids are widely used as food preservatives, as they are very effective at preventing the growth of most species of bacteria and fungi. However, some species of molds can survive and grow in the concentrations of weak acid employed in food and drink products, thereby causing spoilage with resultant risks for food security and health. Current knowledge of weak-acid resistance mechanisms in these fungi is limited, especially in comparison to that in yeasts. We characterized gene functions in the spoilage mold species Aspergillus niger which are important for survival and growth in the presence of weak-acid preservatives. Such identification of weak-acid resistance mechanisms in spoilage molds will help in the design of new strategies to reduce food spoilage in the future.
    Type of Medium: Online Resource
    ISSN: 2379-5042
    URL: Article
    DOI: 10.1128/mSphere.00685-19
    Language: English
    Publisher: American Society for Microbiology
    Publication Date: 2020
    detail.hit.zdb_id: 2844248-9
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  • 3
    Online Resource
    Online Resource
    Metabolic activity in dormant conidia of Aspergillus niger and developmental changes during conidial outgrowth
    Elsevier BV ; 2016
    In:  Fungal Genetics and Biology Vol. 94 ( 2016-09), p. 23-31
    Details
    In: Fungal Genetics and Biology, Elsevier BV, Vol. 94 ( 2016-09), p. 23-31
    Type of Medium: Online Resource
    ISSN: 1087-1845
    URL: Article
    DOI: 10.1016/j.fgb.2016.07.002
    RVK:
    WA 15000
    Language: English
    Publisher: Elsevier BV
    Publication Date: 2016
    detail.hit.zdb_id: 1467659-X
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  • 4
    Online Resource
    Online Resource
    The decarboxylation of the weak-acid preservative, sorbic acid, is encoded by linked genes in Aspergillus spp.
    Elsevier BV ; 2010
    In:  Fungal Genetics and Biology Vol. 47, No. 8 ( 2010-08), p. 683-692
    Details
    In: Fungal Genetics and Biology, Elsevier BV, Vol. 47, No. 8 ( 2010-08), p. 683-692
    Type of Medium: Online Resource
    ISSN: 1087-1845
    URL: Article
    DOI: 10.1016/j.fgb.2010.04.011
    RVK:
    WA 15000
    Language: English
    Publisher: Elsevier BV
    Publication Date: 2010
    detail.hit.zdb_id: 1467659-X
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  • 5
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    Online Resource
    Extreme resistance to weak-acid preservatives in the spoilage yeast Zygosaccharomyces bailii
    Elsevier BV ; 2013
    In:  International Journal of Food Microbiology Vol. 166, No. 1 ( 2013-08), p. 126-134
    Details
    In: International Journal of Food Microbiology, Elsevier BV, Vol. 166, No. 1 ( 2013-08), p. 126-134
    Type of Medium: Online Resource
    ISSN: 0168-1605
    URL: Article
    DOI: 10.1016/j.ijfoodmicro.2013.06.025
    Language: English
    Publisher: Elsevier BV
    Publication Date: 2013
    detail.hit.zdb_id: 2013748-5
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  • 6
    Online Resource
    Online Resource
    Auxotrophy for uridine increases the sensitivity of Aspergillus niger to weak-acid preservatives
    Microbiology Society ; 2008
    In:  Microbiology Vol. 154, No. 4 ( 2008-04-01), p. 1251-1257
    Details
    In: Microbiology, Microbiology Society, Vol. 154, No. 4 ( 2008-04-01), p. 1251-1257
    Type of Medium: Online Resource
    ISSN: 1350-0872 , 1465-2080
    URL: Article
    DOI: 10.1099/mic.0.2007/014332-0
    Language: English
    Publisher: Microbiology Society
    Publication Date: 2008
    detail.hit.zdb_id: 2008736-6
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  • 7
    Online Resource
    Online Resource
    Decarboxylation of Sorbic Acid by Spoilage Yeasts Is Associated with the PAD1 Gene
    American Society for Microbiology ; 2007
    In:  Applied and Environmental Microbiology Vol. 73, No. 20 ( 2007-10-15), p. 6534-6542
    Details
    In: Applied and Environmental Microbiology, American Society for Microbiology, Vol. 73, No. 20 ( 2007-10-15), p. 6534-6542
    Abstract: The spoilage yeast Saccharomyces cerevisiae degraded the food preservative sorbic acid (2,4-hexadienoic acid) to a volatile hydrocarbon, identified by gas chromatography mass spectrometry as 1,3-pentadiene. The gene responsible was identified as PAD1 , previously associated with the decarboxylation of the aromatic carboxylic acids cinnamic acid, ferulic acid, and coumaric acid to styrene, 4-vinylguaiacol, and 4-vinylphenol, respectively. The loss of PAD1 resulted in the simultaneous loss of decarboxylation activity against both sorbic and cinnamic acids. Pad1p is therefore an unusual decarboxylase capable of accepting both aromatic and aliphatic carboxylic acids as substrates. All members of the Saccharomyces genus (sensu stricto) were found to decarboxylate both sorbic and cinnamic acids. PAD1 homologues and decarboxylation activity were found also in Candida albicans, Candida dubliniensis, Debaryomyces hansenii , and Pichia anomala . The decarboxylation of sorbic acid was assessed as a possible mechanism of resistance in spoilage yeasts. The decarboxylation of either sorbic or cinnamic acid was not detected for Zygosaccharomyces, Kazachstania ( Saccharomyces sensu lato), Zygotorulaspora , or Torulaspora , the genera containing the most notorious spoilage yeasts. Scatter plots showed no correlation between the extent of sorbic acid decarboxylation and resistance to sorbic acid in spoilage yeasts. Inhibitory concentrations of sorbic acid were almost identical for S. cerevisiae wild-type and Δ pad1 strains. We concluded that Pad1p-mediated sorbic acid decarboxylation did not constitute a significant mechanism of resistance to weak-acid preservatives by spoilage yeasts, even if the decarboxylation contributed to spoilage through the generation of unpleasant odors.
    Type of Medium: Online Resource
    ISSN: 0099-2240 , 1098-5336
    URL: Article
    DOI: 10.1128/AEM.01246-07
    RVK:
    WA 15000
    Language: English
    Publisher: American Society for Microbiology
    Publication Date: 2007
    detail.hit.zdb_id: 223011-2
    detail.hit.zdb_id: 1478346-0
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  • 8
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    Germination of Aspergillus niger Conidia Is Triggered by Nitrogen Compounds Related to l -Amino Acids
    American Society for Microbiology ; 2014
    In:  Applied and Environmental Microbiology Vol. 80, No. 19 ( 2014-10), p. 6046-6053
    Details
    In: Applied and Environmental Microbiology, American Society for Microbiology, Vol. 80, No. 19 ( 2014-10), p. 6046-6053
    Abstract: Conidial germination is fundamentally important to the growth and dissemination of most fungi. It has been previously shown (K. Hayer, M. Stratford, and D. B. Archer, Appl. Environ. Microbiol. 79:6924–6931, 2013, http://dx.doi.org/10.1128/AEM.02061-13 ), using sugar analogs, that germination is a 2-stage process involving triggering of germination and then nutrient uptake for hyphal outgrowth. In the present study, we tested this 2-stage germination process using a series of nitrogen-containing compounds for the ability to trigger the breaking of dormancy of Aspergillus niger conidia and then to support the formation of hyphae by acting as nitrogen sources. Triggering and germination were also compared between A. niger and Aspergillus nidulans using 2-deoxy- d -glucose (trigger), d -galactose (nontrigger in A. niger but trigger in A. nidulans ), and an N source (required in A. niger but not in A. nidulans ). Although most of the nitrogen compounds studied served as nitrogen sources for growth, only some nitrogen compounds could trigger germination of A. niger conidia, and all were related to l -amino acids. Using l -amino acid analogs without either the amine or the carboxylic acid group revealed that both the amine and carboxylic acid groups were essential for an l -amino acid to serve as a trigger molecule. Generally, conidia were able to sense and recognize nitrogen compounds that fitted into a specific size range. There was no evidence of uptake of either triggering or nontriggering compounds over the first 90 min of A. niger conidial germination, suggesting that the germination trigger sensors are not located within the spore.
    Type of Medium: Online Resource
    ISSN: 0099-2240 , 1098-5336
    URL: Article
    DOI: 10.1128/AEM.01078-14
    RVK:
    WA 15000
    Language: English
    Publisher: American Society for Microbiology
    Publication Date: 2014
    detail.hit.zdb_id: 223011-2
    detail.hit.zdb_id: 1478346-0
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  • 9
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    Structural Features of Sugars That Trigger or Support Conidial Germination in the Filamentous Fungus Aspergillus niger
    American Society for Microbiology ; 2013
    In:  Applied and Environmental Microbiology Vol. 79, No. 22 ( 2013-11-15), p. 6924-6931
    Details
    In: Applied and Environmental Microbiology, American Society for Microbiology, Vol. 79, No. 22 ( 2013-11-15), p. 6924-6931
    Abstract: The asexual spores (conidia) of Aspergillus niger germinate to produce hyphae under appropriate conditions. Germination is initiated by conidial swelling and mobilization of internal carbon and energy stores, followed by polarization and emergence of a hyphal germ tube. The effects of different pyranose sugars, all analogues of d -glucose, on the germination of A. niger conidia were explored, and we define germination as the transition from a dormant conidium into a germling. Within germination, we distinguish two distinct stages, the initial swelling of the conidium and subsequent polarized growth. The stage of conidial swelling requires a germination trigger, which we define as a compound that is sensed by the conidium and which leads to catabolism of d -trehalose and isotropic growth. Sugars that triggered germination and outgrowth included d -glucose, d -mannose, and d -xylose. Sugars that triggered germination but did not support subsequent outgrowth included d -tagatose, d -lyxose, and 2-deoxy- d -glucose. Nontriggering sugars included d -galactose, l -glucose, and d -arabinose. Certain nontriggering sugars, including d -galactose, supported outgrowth if added in the presence of a complementary triggering sugar. This division of functions indicates that sugars are involved in two separate events in germination, triggering and subsequent outgrowth, and the structural features of sugars that support each, both, or none of these events are discussed. We also present data on the uptake of sugars during the germination process and discuss possible mechanisms of triggering in the absence of apparent sugar uptake during the initial swelling of conidia.
    Type of Medium: Online Resource
    ISSN: 0099-2240 , 1098-5336
    URL: Article
    DOI: 10.1128/AEM.02061-13
    RVK:
    WA 15000
    Language: English
    Publisher: American Society for Microbiology
    Publication Date: 2013
    detail.hit.zdb_id: 223011-2
    detail.hit.zdb_id: 1478346-0
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  • 10
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    The Preservative Sorbic Acid Targets Respiration, Explaining the Resistance of Fermentative Spoilage Yeast Species
    American Society for Microbiology ; 2020
    In:  mSphere Vol. 5, No. 3 ( 2020-06-24)
    Details
    In: mSphere, American Society for Microbiology, Vol. 5, No. 3 ( 2020-06-24)
    Abstract: A small number (10 to 20) of yeast species cause major spoilage in foods. Spoilage yeasts of soft drinks are resistant to preservatives like sorbic acid, and they are highly fermentative, generating large amounts of carbon dioxide gas. Conversely, many yeast species derive energy from respiration only, and most of these are sorbic acid sensitive and so prevented from causing spoilage. This led us to hypothesize that sorbic acid may specifically inhibit respiration. Tests with respirofermentative yeasts showed that sorbic acid was more inhibitory to both Saccharomyces cerevisiae and Zygosaccharomyces bailii during respiration (of glycerol) than during fermentation (of glucose). The respiration-only species Rhodotorula glutinis was equally sensitive when growing on either carbon source, suggesting that ability to ferment glucose specifically enables sorbic acid-resistant growth. Sorbic acid inhibited the respiration process more strongly than fermentation. We present a data set supporting a correlation between the level of fermentation and sorbic acid resistance across 191 yeast species. Other weak acids, C 2 to C 8 , inhibited respiration in accordance with their partition coefficients, suggesting that effects on mitochondrial respiration were related to membrane localization rather than cytosolic acidification. Supporting this, we present evidence that sorbic acid causes production of reactive oxygen species, the formation of petite (mitochondrion-defective) cells, and Fe-S cluster defects. This work rationalizes why yeasts that can grow in sorbic acid-preserved foods tend to be fermentative in nature. This may inform more-targeted approaches for tackling these spoilage organisms, particularly as the industry migrates to lower-sugar drinks, which could favor respiration over fermentation in many spoilage yeasts. IMPORTANCE Spoilage by yeasts and molds is a major contributor to food and drink waste, which undermines food security. Weak acid preservatives like sorbic acid help to stop spoilage, but some yeasts, commonly associated with spoilage, are resistant to sorbic acid. Different yeasts generate energy for growth by the processes of respiration and/or fermentation. Here, we show that sorbic acid targets the process of respiration, so fermenting yeasts are more resistant. Fermentative yeasts are also those usually found in spoilage incidents. This insight helps to explain the spoilage of sorbic acid-preserved foods by yeasts and can inform new strategies for effective control. This is timely as the sugar content of products like soft drinks is being lowered, which may favor respiration over fermentation in key spoilage yeasts.
    Type of Medium: Online Resource
    ISSN: 2379-5042
    URL: Article
    DOI: 10.1128/mSphere.00273-20
    Language: English
    Publisher: American Society for Microbiology
    Publication Date: 2020
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