Comparative Transcriptome Analysis of Penicillium citrinum Cultured with Different Carbon Sources Identifies Genes Involved in Citrinin Biosynthesis

Sorbremnoids A and B: NLRP3 Inflammasome Inhibitors Discovered from Spatially Restricted Crosstalk of Biosynthetic Pathways

Crosstalk-oriented chemical evolution of natural products (NPs) is an efficacious strategy for generating novel skeletons through coupling reactions between NP fragments. In this study, two NOD-like receptor protein 3 (NLRP3) inflammasome inhibitors, sorbremnoids A and B (1 and 2), with unprecedented chemical architectures were identified from a fungus Penicillium citrinum. Compounds 1 and 2 exemplify rare instances of hybrid NPs formed via a major facilitator superfamily (MFS)-like enzyme by coupling reactive intermediates from two separate biosynthetic gene clusters (BGCs), pcisor and pci56. Both sorbremnoids A and B are NLRP3 inflammasome inhibitors. Sorbremnoid A demonstrated strong inhibition of IL-1β by directly binding to the NLRP3 protein, inhibiting the assembly and activation of the NLRP3 inflammasome in vitro, with potential application in diabetic refractory wound healing through the suppression of excessive inflammatory responses. This research will inspire the development of anti-NLRP3 inflammasome agents as lead treatments and enhance knowledge pertaining to NPs derived from biosynthetic crosstalk.

Genomic, transcriptomic, and ecological diversity of Penicillium species in cheese rind microbiomes

Although Penicillium molds can have significant impacts on agricultural, industrial, and biomedical systems, the ecological roles of Penicillium species in many microbiomes are not well characterized. Here we utilized a collection of 35 Penicillium strains isolated from cheese rinds to broadly investigate the genomic potential for secondary metabolism in cheese-associated Penicillium species, the impact of Penicillium on bacterial community assembly, and mechanisms of Penicillium-bacteria interactions. Using antiSMASH, we identified 1558 biosynthetic gene clusters, 406 of which were mapped to known pathways, including several mycotoxins and antimicrobial compounds. By measuring bacterial abundance and fungal mRNA expression when culturing representative Penicillium strains with a cheese rind bacterial community, we observed divergent impacts of different Penicillium strains, from strong inhibitors of bacterial growth to those with no impact on bacterial growth or community composition. Through differential mRNA expression analyses, Penicillium strains demonstrated limited differential gene expression in response to the bacterial community. We identified a few shared responses between the eight tested Penicillium strains, primarily upregulation of nutrient metabolic pathways, but we did not identify a conserved fungal response to growth in a multispecies community. These results in tandem suggest high variation among cheese-associated Penicillium species in their ability to shape bacterial community development and highlight important ecological diversity within this iconic genus.

Peniciriols A and B, two new citrinin derivatives from an endophytic fungus Penicillum citrinum TJNZ-27

Two undescribed citrinin derivatives, named peniciriols A-B (1-2), together with six known compounds were isolated from endophytic fungus Penicillum citrinum TJNZ-27. The structures of two new compounds were well established by the detail interpretation of NMR and HRESIMS data as well as ECD measurement powered by molecular calculation. Among them, compound 1 shared an unprecedented dimerized citrinin skeleton with the formation of an intriguing 9H-xanthene ring system, whereas compound 2 possess a highly substituted phenylacetic acid skeleton, which was rarely-occurring in natural secondary metabolites. Moreover, these novel compounds were tested for cytotoxic and antibacterial activities, whereas these novel compounds did not exhibit any noticeable cytotoxic or antibacterial activities.

Diversity of Cellulolytic Microorganisms Associated with the Subterranean Termite Reticulitermes grassei

Reticulitermes grassei is a subterranean termite species that forages on woody structures of the Iberian Peninsula, and is often a building and crops pest. A total of 23 microorganisms associated with the activity of R. grassei were isolated from colonized ecosystems in southern Spain. They were morphologically and molecularly characterized, with fungi being the most prevalent ones. The fungi showed high values of optimum growth temperature, suggesting that they could be able to survive and develop in warm regions. Their cellulolytic activity was tested in carboxymethylcellulose (CMC) agar, concluding that all fungal isolates produce cellulases, and the enzymatic index (EI) was revealed in CMC agar with Gram’s iodine solution, with Penicillium citrinum showing the highest EI and Trichoderma longibrachiatum the highest mycelial growth rate on CMC. A preliminary microorganism dispersion assay was carried out with the termites, concluding that these insects may have a positive influence on fungal dispersion and the subsequent colonization of new substrates. Our study suggests that fungi associated with R. grassei may potentially be of interest in biotechnological fields such as biofuel production and the food industry.

How to Completely Squeeze a Fungus-Advanced Genome Mining Tools for Novel Bioactive Substances

Fungal species have the capability of producing an overwhelming diversity of bioactive substances that can have beneficial but also detrimental effects on human health. These so-called secondary metabolites naturally serve as antimicrobial "weapon systems", signaling molecules or developmental effectors for fungi and hence are produced only under very specific environmental conditions or stages in their life cycle. However, as these complex conditions are difficult or even impossible to mimic in laboratory settings, only a small fraction of the true chemical diversity of fungi is known so far. This also implies that a large space for potentially new pharmaceuticals remains unexplored. We here present an overview on current developments in advanced methods that can be used to explore this chemical space. We focus on genetic and genomic methods, how to detect genes that harbor the blueprints for the production of these compounds (i.e., biosynthetic gene clusters, BGCs), and ways to activate these silent chromosomal regions. We provide an in-depth view of the chromatin-level regulation of BGCs and of the potential to use the CRISPR/Cas technology as an activation tool.

Insights into the Underlying Mechanism of Ochratoxin A Production in Aspergillus niger CBS 513.88 Using Different Carbon Sources

Aspergillus niger produces carcinogenic ochratoxin A (OTA), a serious food safety and human health concern. Here, the ability of A. niger CBS 513.88 to produce OTA using different carbon sources was investigated and the underlying regulatory mechanism was elucidated. The results indicated that 6% sucrose, glucose, and arabinose could trigger OTA biosynthesis and that 1586 differentially expressed genes (DEGs) overlapped compared to a non-inducing nutritional source, peptone. The genes that participated in OTA and its precursor phenylalanine biosynthesis, including pks, p450, nrps, hal, and bzip, were up-regulated, while the genes involved in oxidant detoxification, such as cat and pod, were down-regulated. Correspondingly, the activities of catalase and peroxidase were also decreased. Notably, the novel Gal4-like transcription factor An12g00840 (AnGal4), which is vital in regulating OTA biosynthesis, was identified. Deletion of AnGal4 elevated the OTA yields by 47.65%, 54.60%, and 309.23% using sucrose, glucose, and arabinose as carbon sources, respectively. Additionally, deletion of AnGal4 increased the superoxide anion and H₂O₂ contents, as well as the sensitivity to H₂O₂, using the three carbon sources. These results suggest that these three carbon sources repressed AnGal4, leading to the up-regulation of the OTA biosynthetic genes and alteration of cellular redox homeostasis, ultimately triggering OTA biosynthesis in A. niger.

Monascus spp. and citrinin: Identification, selection of Monascus spp. isolates, occurrence, detection and reduction of citrinin during the fermentation of red fermented rice

Red fermented rice (RFR) is rice fermented using Monascus spp. This product contains monacolin K, providing health benefits including mitigation of diarrhoea and improving blood circulation. RFR can produce pigments that can act as natural colour and flavouring agents. However, Monascus spp. (a fungal starter to ferment RFR) can also produce the mycotoxin, citrinin (CIT) which is believed to have adverse effects on human health. CIT in RFR has been reported worldwide by using different methods of detection. This review focuses on the production of RFR by solid-state fermentation (SSF) and submerged fermentation (SmF), the occurrence of CIT in RFR, CIT quantification, the factors affecting the growth of Monascus spp., pigments and CIT production in RFR, and possible methods to reduce CIT in RFR. This review will help the food industries, researchers, and consumers understand the risk of consuming RFR, and the possibility of controlling CIT in RFR.

Carbon catabolite regulation of secondary metabolite formation, an old but not well-established regulatory system

Secondary microbial metabolites have various functions for the producer microorganisms, which allow them to interact and survive in adverse environments. In addition to these functions, other biological activities may have clinical relevance, as diverse as antimicrobial, anticancer and hypocholesterolaemic effects. These metabolites are usually formed during the idiophase of growth and have a wide diversity in their chemical structures. Their synthesis is under the impact of the type and concentration of the culture media nutrients. Some of the molecular mechanisms that affect the synthesis of secondary metabolites in bacteria (Gram-positive and negative) and fungi are partially known. Moreover, all microorganisms have their peculiarities in the control mechanisms of carbon sources, even those belonging to the same genus. This regulatory knowledge is necessary to establish culture conditions and manipulation methods for genetic improvement and product fermentation. As the carbon source is one of the essential nutritional factors for antibiotic production, its study has been imperative both at the industrial and research levels. This review aims to draw the utmost recent advances performed to clarify the molecular mechanisms of the negative effect exerted by the carbon source on the secondary metabolite formation, emphasizing those found in Streptomyces, one of the genera most profitable antibiotic producers.

A Combined Analysis of Transcriptome and Proteome Reveals the Inhibitory Mechanism of a Novel Oligosaccharide Ester against Penicillium italicum

Blue mold caused by Penicillium italicum is one of the most serious postharvest diseases of citrus fruit. The aim of this study was to investigate the inhibitory effect of a novel oligosaccharide ester, 6-O-β-L-mannopyranosyl-3-O-(2-methylbutanoyl)-4-O-(8-methyldecanoyl)-2-O-(4-methyl-hexanoyl) trehalose (MTE-1), against P. italicum. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM), along with transcriptome and proteome analysis also, were conducted to illuminate the underlying mechanism. Results showed that MTE-1 significantly inhibited P. italicum growth in vitro in a dose-dependent manner. Moreover, MTE-1 suppressed the disease development of citrus fruit inoculated with P. italicum. Furthermore, ultrastructure observation, as well as transcriptome and proteome analysis, indicated that MTE-1 treatment damaged the cell wall and plasma membrane in spores and mycelia of P. italicum. In addition, MTE-1 regulated genes or proteins involved in primary metabolism, cell-wall metabolism, and pathogenicity. These results demonstrate that MTE-1 inhibited P. italicum by damaging cell walls and membranes and disrupting normal cellular metabolism. These findings contribute to the understanding of the possible molecular action of MTE-1. Finally, MTE-1 also provides a new natural strategy for controlling diseases in postharvest fruit.

The mutated Bacillus amyloliquefaciens strain shows high resistance to Aeromonas hydrophila and Aeromonas veronii in grass carp

Bacillus amyloliquefaciens X030 (BaX030) has broad-spectrum antibacterial activity against the fish pathogens Aeromonas hydrophila and Aeromonas veronii. To improve its antibacterial effect, BaX030 was subjected to compound mutagenesis of atmospheric and room temperature plasma (ARTP) and nitrosoguanidine (NTG). The results showed that, compared with the original strain, the production of macrolactin A and oxydifficidin in mutated strain N-11 increased to 39 % and 268 %, respectively. The re-sequencing analysis suggested that there were SNPs and InDels in the gene clusters focused on the sucrose utilization pathway, glycolysis pathway and fatty acid synthesis pathway. Scanning electron microscopy revealed that strain N-11 became thin and long. The qRT-PCR results indicated that the expression of immune factors in the liver or kidney tissue of grass carp increased after feeding with N-11. H&E staining and protection experiments also showed that the mortality and surface symptoms of grass carp infected by the two pathogens were significantly reduced. The study identified a probiotic strain with potential application value in aquaculture production and provided a new strategy for the discovery of new strains with higher antibacterial biological activity.

Penicillium expansum: biology, omics, and management tools for a global postharvest pathogen causing blue mould of pome fruit

Blue mould, caused primarily by Penicillium expansum, is a major threat to the global pome fruit industry, causing multimillion-dollar losses annually. The blue mould fungus negatively affects fruit quality, thereby reducing fresh fruit consumption, and significantly contributes to food loss. P. expansum also produces an array of mycotoxins that are detrimental to human health. Management options are limited and the emergence of fungicide-resistant Penicillium spp. makes disease management difficult, therefore new approaches and tools are needed to combat blue mould in storage. This species profile comprises a comprehensive literature review of this aggressive pathogen associated with pomes (apple, pear, quince), focusing on biology, mechanisms of disease, control, genomics, and the newest developments in disease management.

TAXONOMY

Penicillium expansum Link 1809. Domain Eukaryota, Kingdom Fungi, Phylum Ascomycota, Subphylum Pezizomycotina, Class Eurotiomycetes, Subclass: Eurotiomycetidae, Order Eurotiales; Family Trichocomaceae, Genus Penicillium, Species expansum.

BIOLOGY

A wide host range necrotrophic postharvest pathogen that requires a wound (e.g., stem pull, punctures, bruises, shoulder cracks) or natural openings (e.g., lenticel, stem end, calyx sinus) to gain ingress and infect.

TOXINS

Patulin, citrinin, chaetoglobosins, communesins, roquefortine C, expansolides A and B, ochratoxin A, penitrem A, rubratoxin B, and penicillic acid.

HOST RANGE

Primarily apples, European pear, Asian pear, medlar, and quince. Blue mould has also been reported on stone fruits (cherry, plum, peach), small fruits (grape, strawberry, kiwi), and hazel nut.

DISEASE SYMPTOMS

Blue mould initially appears as light tan to dark brown circular lesions with a defined margin between the decayed and healthy tissues. The decayed tissue is soft and watery, and blue-green spore masses appear on the decayed area, starting at the infection site and radiating outward as the decayed area ages.

DISEASE CONTROL

Preharvest fungicides with postharvest activity and postharvest fungicides are primarily used to control decay. Orchard and packinghouse sanitation methods are also critical components of an integrated pest management strategy.

USEFUL WEBSITES

Penn State Tree Fruit Production Guide (https://extension.psu.edu/forage-and-food-crops/fruit), Washington State Comprehensive Tree Fruit (http://treefruit.wsu.edu/crop-protection/disease-management/blue-mold/), The Apple Rot Doctor (https://waynejurick.wixsite.com/applerotdr), penicillium expansum genome sequences and resources (https://www.ncbi.nlm.nih.gov/genome/browse/#!/eukaryotes/11336/).

Penicillium spp. mycotoxins found in food and feed and their health effects

Mycotoxins are toxic secondary metabolites produced by fungi. These compounds have different structures and target different organs, acting at different steps of biological processes inside the cell. Around 32 mycotoxins have been identified in fungal Penicillium spp. isolated from food and feed. Some of these species are important pathogens which contaminate food, such as maize, cereals, soybeans, sorghum, peanuts, among others. These microorganisms can be present in different steps of the food production process, such as plant growth, harvest, drying, elaboration, transport, and packaging. Although some Penicillium spp. are pathogens, some of them are used in elaboration of processed foods, such as cheese and sausages. This review summarises the Penicillium spp. mycotoxin toxicity, focusing mainly on the subgenus Penicillium, frequently found in food and feed. Toxicity is reviewed both in animal models and cultured cells. Finally, some aspects of their regulations are discussed.

Complete mitochondrial genome and phylogenetic analysis of Penicillium citrinum in dark tea

Penicillium citrinum is a common polluting microorganism in dark tea production. Our study was performed to report the complete mitochondrial genome of P. citrinum. The mitochondrial genome of P. citrinum was a circular DNA molecule of 27,537 bp in length, encoding 42 genes as follows: 15 PCGs, two rRNAs, 24 tRNAs, and an independent ORF. A (36.14%), T (37.06%), C (11.83%), and G (14.98%) was composed of genomic bases. In addition, phylogenetic analysis showed that Penicillium sp. exhibited a closest relationship with the taxonomic status of P. citrinum.

Effects of Different Carbon Sources on Fumonisin Production and FUM Gene Expression by Fusarium proliferatum

Fusarium proliferatum can infect many crops and then produce fumonisins that are very harmful to humans and animals. Previous study indicates that carbon sources play important roles in regulating the fumonisin biosynthesis. Unfortunately, there is limited information on the effects of carbon starvation in comparison with the carbon sources present in the host of fumonisin production in F. proliferatum. Our results indicated that F. proliferatum cultivated in the Czapek's broth (CB) medium in the absence of sucrose could greatly induce production of fumonisin, while an additional supplementation of sucrose to the culture medium significantly reduced the fumonisin production. Furthermore, cellulose and hemicellulose, and polysaccharide extracted from banana peel, which replaced sucrose as the carbon source, can reduce the production of fumonisin by F. proliferatum. Further work showed that these genes related to the synthesis of fumonisin, such as FUM1 and FUM8, were significantly up-regulated in the culture medium in the absence of sucrose. Consistent with fumonisin production, the expressions of FUM gene cluster and ZFR1 gene decreased after the addition of sucrose. Moreover, these genes were also significantly down-regulated in the presence of cellulose, hemicellulose or polysaccharide extracted from peel. Altogether, our results suggested that fumonisin production was regulated in F. proliferatum in response to different carbon source conditions, and this regulation might be mainly via the transcriptional level. Future work on these expressions of the fumonisin biosynthesis-related genes is needed to further clarify the response under different carbon conditions during the infection of F. proliferatum on banana fruit hosts. The findings in this study will provide a new clue regarding the biological effect of the fumonisin production in response to environmental stress.

Impact of veA on the development, aggressiveness, dissemination and secondary metabolism of Penicillium expansum

Penicillium expansum, the causal agent of blue mould disease, produces the mycotoxins patulin and citrinin amongst other secondary metabolites. Secondary metabolism is associated with fungal development, which responds to numerous biotic and abiotic external triggers. The global transcription factor VeA plays a key role in the coordination of secondary metabolism and differentiation processes in many fungal species. The specific role of VeA in P. expansum remains unknown. A null mutant PeΔveA strain and a complemented PeΔveA:veA strain were generated in P. expansum and their pathogenicity on apples was studied. Like the wild-type and the complemented strains, the null mutant PeΔveA strain was still able to sporulate and to colonize apples, but at a lower rate. However, it could not form coremia either in vitro or in vivo, thus limiting its dissemination from natural substrates. The impact of veA on the expression of genes encoding proteins involved in the production of patulin, citrinin and other secondary metabolites was evaluated. The disruption of veA drastically reduced the production of patulin and citrinin on synthetic media, associated with a marked down-regulation of all genes involved in the biosynthesis of the two mycotoxins. Moreover, the null mutant PeΔveA strain was unable to produce patulin on apples. The analysis of gene expression revealed a global impact on secondary metabolism, as 15 of 35 backbone genes showed differential regulation on two different media. These findings support the hypothesis that VeA contributes to the pathogenicity of P. expansum and modulates its secondary metabolism.

Elevated CO2 delays the early development of scleractinian coral Acropora gemmifera

The effects of elevated CO₂ on the early life stages of coral were investigated by culturing the pelagic larvae and new recruits of Acropora gemmifera at three concentrations of CO₂ (corresponding to pH = 8.1, 7.8 and 7.5, respectively). Acidified seawater resulted in fewer A. gemmifera larvae settling, and led to the production of smaller new recruits by slowing the development of the skeleton. The delayed development of new recruits due to elevated CO₂ was consistent with the downregulation of calcification related genes. Several genes related to HCO₃^- and Ca²⁺ transporters were downregulated by elevated CO₂, with solute carriers (SLC) (membrane transport proteins) possibly playing an important role. The downregulation of these membrane transport proteins might suppress the transport of calcium, bicarbonate and organic matter, resulting in the delayed development of A. gemmifera.