Production of Satratoxin G and H Is Tightly Linked to Sporulation in Stachybotrys chartarum

Abstract

Stachybotrys chartarum is a toxigenic fungus that is frequently isolated from damp building materials or improperly stored forage. Macrocyclic trichothecenes and in particular satratoxins are the most potent mycotoxins known to be produced by this fungus. Exposure of humans or animals to these secondary metabolites can be associated with severe health problems. To assess the pathogenic potential of S. chartarum isolates, it is essential to cultivate them under conditions that reliably promote toxin production. Potato dextrose agar (PDA) was reported to be the optimal nutrition medium for satratoxin production. In this study, the growth of S. chartarum genotype S strains on PDA from two manufacturers led to divergent results, namely, well-grown and sporulating cultures with high satratoxin concentrations (20.8 ± 0.4 µg/cm2) versus cultures with sparse sporulation and low satratoxin production (0.3 ± 0.1 µg/cm2). This finding is important for any attempt to identify toxigenic S. chartarum isolates. Further experiments performed with the two media provided strong evidence for a link between satratoxin production and sporulation. A comparison of three-point and one-point cultures grown on the two types of PDA, furthermore, demonstrated an inter-colony communication that influences both sporulation and mycotoxin production of S. chartarum genotype S strains.

A Chemically Defined Medium That Supports Mycotoxin Production by Stachybotrys chartarum Enabled Analysis of the Impact of Nitrogen and Carbon Sources on the Biosynthesis of Macrocyclic Trichothecenes and Stachybotrylactam

“…Mycotoxins of several fungi are known to be associated with sporulation and are secreted by growing colonies ( 61 ), and a link between secondary metabolism and sporulation is a common feature in many filamentous fungi ( 62 ). Previously, similar results were obtained with S. chartarum ( 57 ), and, therefore, our observations are in good agreement with published data.…”

“…We included three S. chartarum strains in this study that are known for their effective production of macrocyclic trichothecenes (MTs) and stachybotrylactam (STLAC) ( 6 , 9 , 38 , 54 ). Since our previously published data demonstrated that satratoxin production is tightly linked to sporulation ( 57 ), this work considered the size of the resulting colonies and their level of sporulation. The selected strains come from three substrates, namely, oats (ATCC 34916), building material from an apartment in Oakland (IBT 40293), and oregano (DSM 114129).…”

“…The cultures were checked microscopically for their identity. Five single-spore isolates per strain (≙five biological replicates) were prepared as described previously ( 57 ) to ensure that the used strains were pure and to confirm the species, chemotype, and genotype. The respective species identifications were confirmed for all strains by matrix-assisted laser desorption ionization–time of flight mass spectrometry (MALDI-TOF MS) ( 87 ).…”

“…However, PDA and rice contain complex components, which makes it difficult to identify factors that influence mycotoxin production. Another drawback of PDA is that its complex components can vary, and this can have a dramatic impact on the amounts of mycotoxins that are produced ( 57 ). In other fungi, defined media have been established, such as Aspergillus minimal medium (AMM) ( 58 ), in which all ingredients are known and can be replaced or varied in concentration.…”

Identification of Virulence Factors in Entomopathogenic Aspergillus flavus Isolated from Naturally Infected Rhipicephalus microplus

“…A thorough search using the AntiFungi algorithm revealed the noteworthy secondary metabolite napthopyrone, a fungal predator-protecting secondary metabolite [ 70 ] ( Table 7 ). Moreover, comparative genomics results revealed the presence of toxin-related genes, comprising those related to killer toxin α/β, satratoxin, and aflatoxins identified in fungal genera such as Kluyveromyces , Stachybotrys , Aspergillus , the teleomorph genus Neosartorya , and the KP4 killer toxin from Ustilago maydis P4 virus [ 10 , 71 , 72 ] ( Table 8 ).…”