Abstract
Aspergillus niger is perhaps the most important fungus used in biotechnology, and is also one of the most commonly encountered fungi contaminating foods and feedstuffs, and occurring in soil and indoor environments. Many of its industrial applications have been given GRAS status (generally regarded as safe). However, A. niger has the potential to produce two groups of potentially carcinogenic mycotoxins: fumonisins and ochratoxins. In this study all available industrial and many non-industrial strains of A. niger (180 strains) as well as 228 strains from 17 related black Aspergillus species were examined for mycotoxin production. None of the related 17 species of black Aspergilli produced fumonisins. Fumonisins (B2, B4, and B6) were detected in 81% of A. niger, and ochratoxin A in 17%, while 10% of the strains produced both mycotoxins. Among the industrial strains the same ratios were 83%, 33% and 26% respectively. Some of the most frequently used strains in industry NRRL 337, 3112 and 3122 produced both toxins and several strains used for citric acid production were among the best producers of fumonisins in pure agar culture. Most strains used for other biotechnological processes also produced fumonisins. Strains optimized through random mutagenesis usually maintained their mycotoxin production capability. Toxigenic strains were also able to produce the toxins on media suggested for citric acid production with most of the toxins found in the biomass, thereby questioning the use of the remaining biomass as animal feed. In conclusion it is recommended to use strains of A. niger with inactive or inactivated gene clusters for fumonisins and ochratoxins, or to choose isolates for biotechnological uses in related non-toxigenic species such as A. tubingensis, A. brasiliensis, A vadensis or A. acidus, which neither produce fumonisins nor ochratoxins.
Highlights
Aspergillus niger is one of the most important industrial filamentous fungal species used in biotechnology [1,2] where it is used extensively for organic acid production [3,4,5] and for the production of extracellular enzymes [6]
Most biotechnological isolates were Aspergillus niger sensu stricto, some strains (23%) originally identified as A. niger were re-identified as A. tubingensis, A. brasiliensis, A. acidus or A. carbonarius (Table S1)
Identification of a large number of strains from soil, foods and other habitats showed that A. niger was most common among the black Aspergilli (44%), but that A. tubingensis was approximately half as common (20%), while A. acidus (10%), A. carbonarius (7%) A. brasiliensis (4%) were less common, and the remaining species in the black Aspergilli were rare
Summary
Aspergillus niger is one of the most important industrial filamentous fungal species used in biotechnology [1,2] where it is used extensively for organic acid production [3,4,5] and for the production of extracellular enzymes [6]. Three strains of A. niger have already been full genome sequenced: ATCC 1015, NRRL 3 and CBS 513.88 [1,2,15]. These strains have subsequently been examined intensively using transcriptomics and metabolomics to explore and understand growth, differentiation, chemistry and physiology of the species [1,14,16,17,18,19,20]. Surveys of isolates from coffee, grapes and raisins have shown that many produce fumonisins strongly indicating that A. niger is responsible for the presence of low amounts of FB2 in almost a quarter of all examined wine samples [25,26] as well as in half the examined raisins and grapes [27,28,29]
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