Fungi are found predominantly in all environments and have substantial roles in preserving eco-balance, diversity, and sustainability ^[1][2][3][1,2,3]. They have demonstrated a wide array of industrial and biotechnological potentials ^[1][4][5][6][1,4,5,6]. Additionally, they are an important source of metabolites with unique chemical skeletons that have the potential for discovering drugs of clinical relevance ^{[7][8][9][10][11][12]}[7,8,9,10,11,12]. This was evident by many reported fungi-derived drugs that are in use, for example camptothecin, cyclosporine, paclitaxel, torreyanic acid, compactin, vincristine, lovastatin, and cytarabine ^[13][14][15][13,14,15]. Additionally, they are a pool of new scaffolds, which can be further modified to achieve the needed action [16]. Many of these metabolites can be obtained in considerable amounts and at a feasible cost through fermentation utilizing genetically modified or wild type fungi [15]. Regardless of the remarkable advancement in discovering drugs that provide treatment for most ailments, epidemics, and infections, novel drugs are requested to counter the reported resistance of some diseases and infections to the existing drugs ^[17][18][19][17,18,19]. Despite the biodiversity of the fungi kingdom, only a limited number of fungi have been explored for their capacity to produce bioactive metabolites.

Stachybotryschartarum (black mold) (Stachybotriaceae, S. atra or S. alternans) is a toxigenic fungus that is widely present in the indoor air of buildings or homes which have water damage or sustained flooding from roofs, broken pipes, floor or wall leaks, and condensation. S. chartarum a hydrophilic fungus, needing wet conditions for maintaining and initiating its growth. It is also found on gypsum, cellulose-based ceiling tiles, fiberglass, wallpaper, paper products, natural fiber carpets, insulated pipes paper covering, wood and wood paneling, and organic debris, as well as soil, grains, and litter ^[20][21][20,21]. S. chartarum is one of the most common pathogenic indoor fungi that is capable of producing mycotoxins, having life-threatening health impacts [21]. Several reports stated that the exposure to this fungus or its mycotoxins through contaminated indoor air and construction material causes severe fungi-mediated sick building illnesses and even human death ^[20][21][22][20,21,22]. The common symptoms of this illness are fatigue, chest tightness, mucosal irritation, and headache [20]. It can also cause respiratory disorders that range from cough and congestion to more dangerous syndromes including bronchiectasis, alveolitis, and pulmonary fibrosis [23]. It was also found that exposure to this fungus has been related to infants’ pulmonary hemorrhage outbreaks [24]. Further, the exposure to S. chartarum in damp environments exceeds the threshold of sensitization in susceptible people [25]. This fungus causes stachybotryotoxicosis in horses and other animals [26]. The fungus’ biosynthesized macrocyclic trichothecenes are considered one of the most powerful inhibitors for protein synthesis. Additionally, it produces biometabolites (e.g. atranones and spirodrimanes), protein factors (e.g. stachylysin and hemolysin), immunosuppressive agents, and proteinases (e.g. serine proteases) that are attributed to pulmonary destruction, hemosiderosis, and hemorrhage ^[27][28][29][27,28,29]. Most of the reported studies on S. chartarum highlighted its pathogenic influences on humans and animals ^{[21][30][31][32]}[21,30,31,32].

2. S. chartarum Enzymes and Their Possible Applications

Fungi possess diverse digestive-enzyme batteries. They can utilize agro-industrial wastes by yielding diverse enzyme types, such as xylanases, cellulases, amylases, laccases, and pectinases. These enzymes play a substantial ecological role in lignin-cellulosic materials’ decomposition and can be utilized in various biotechnological applications. Polythene wastes are adversely affecting the environment due to strong reluctance towards degradation [33]. Biodegradation is one of the favorable solutions for conquering this problem [34]. S. chartarum was found to possess degradation potential for biodegradable and low-density polythene [34]. Andersen et al. also reported that the indoor strain of S. chartarum had no or little xylanolytic and cellulolytic potentials in the AZCL (Azurine-cross-linked) assay [35]. On the contrary, it exhibited amylolytic and cellulolytic potential ^[36][37][36,37] and had a lignocellulose complex-degrading enzymes system [28]. Kordula et al. purified and characterized stachyrase A (chymotrypsin-like serine protease) from S. chartarum that had wide substrate specificity and hydrolyzed various physiologically potential proteins, protease inhibitors, and collagen in the lung [38].

2.1. Laccases

Enzymes’ oxidizing phenols have diversified applications in various industries, including paper and wood pulp delignification, textile (dye and stain bleaching), and biosensors. Laccases are phenol oxidases that can oxidize several aromatic compounds ^[4][39][40][4,39,40]. Fungal laccases have a crucial role in developing the fruiting body, as well as in lignin degradation [41]. Some laccases are produced upon exposure to phenolic substances. Mander et al. purified a laccase enzyme from S. chartarum and its gene was separated and expressed in Trichoderma reesei, Aspergillus niger, and A. nidulans. This enzyme oxidized the artificial substrate ABTS (2,2-azino-di-(3-ethylbenzthiazolinsulfonate) [42]. Further, Janssen et al. stated that the insertion of the peptide sequences IERSAPATAPPP, YGYLPSR, SLLNATK, KASAPAL, and CKASAPALC inserted in the C-terminal of S. chartarum laccase by recombinant DNA tools resulted in laccase- peptide fusions that selectively targeted carotenoid stains and displayed enhanced bleaching potential on stained fabrics [43]. This suggested that the modification of certain enzymes could improve their activity, suggesting a new area of research in this fungus.

2.2. Mannanases

Mannans are constituents of hemicellulose that are found in plants, some algae, microorganisms, and tremella [44]. They include gluco-, galacto-, and galactogluco-mannanase well as linear mannan [45]. They have diverse applications, for example KG (konjac glucomannan) and LBG (locust bean gum, galactomannan) are commonly utilized for chronic diseases and obesity prevention and viscosity-boosting food additives, respectively ^[46][47][46,47]. Mannans’ degradation is accomplished by various GHs (glycoside hydrolases) such as β-mannanase, β-mannosidase, β-glucosidase, acetyl-mannan-esterase, and α-galactosidase producing manno-oligosaccharides [48]. The later were utilized as prebiotics that enhance immune responses and modulate gut microbiota [49]. Yang et al. identified two β-mannanase genes (s331 and s16942) from S. chartarum that were expressed in Aspergillus niger with high protein titers and activities [50].

2.3. β-Glucanases

β-Glucans comprise glucose polymers heterogeneous group, including lichenan (β-1,4-1,3-glucan), cellulose (β-1,4-glucan), β-1,3(4)-glucan, and laminarin (β-1,3-glucan). Their hydrolysis is catalyzed by various kinds of β-glucanases, such as lichenases, cellulases, laminarinases, and β-1,3(4)-glucanases [51]. Lichenases are produced by various microorganisms, including fungi and bacteria, and have remarkable applications in detergent, food, feed, brewing, and wine industries as well as biodiesel and bioethanol production [51]. The expression of the gene Cel12A isolated from rotting cellulose rag-associated-S. chartarum by Picart et al. was triggered by rice straw than 0.1% glucose or 1% lactose ^[52][53][52,53]. The resulting enzyme Cel12A (GH12 family) had a lichenase potential. It also exhibited high potential towards barley mixed glucans and lichenan and low effectiveness on cellulose. Hence, Cel12A could have potential applications in various industries [53]. r-ScEG12, a recombinant glucanase gene from S. chartarum, belonging to GH12 (glycosyl hydrolase family12), was purified and expressed in Pichia pastoris [54]. It was found that Mn²⁺ and Cu²⁺ (%inhibition 50.97 and 71.64%, respectively) prohibited its activity, while Ca²⁺ and Na⁺ enhanced the activity. This proved the capacity of S. chartarum to secrete endoglucanases that could be beneficial for industrial use [54]. Xylanase is the principal enzyme accountable for hemicellulose hydrolysis. The xya6205a gene obtained from S. chartarum was expressed in A. niger. The obtained xylanase had optimum potential at 5.8 pH and 50℃ temperature and maintained 83% activity after 18 h in the alkaline buffer [55].

2.4. Fucoidanases and Alginate Lyases

Alginate and fucoidan are polysaccharides found in brown seaweed that have wide potential applications because of their diversified bioactivities. Alginate lyases are polysaccharide lyases that hydrolyze alginate by cleaving the glycosidic bond to produce oligo-alginates, which have a substantial role in feed, food, nutraceutical, biofuel, and pharmaceutical industries [56]. In addition, they possess film-formation, emulsifying, gelling, and plant-growth promoting capacities [57]. Fucoidan showed antioxidant, anticoagulant, antiviral, anticancer, anti-inflammatory, and immunomodulatory capacities ^[56][58][56,58]. In spite of these beneficial bioactivities, fucoidan molecules possess structural variation, high molecular weight, and viscous nature that limit their therapeutic and pharmaceutical applications, however, low molecular-weight fucoidan-derived oligosaccharides have a wide potential for applications [59]. Fucoidanases are accountable for fucoidan hydrolysis to fucooligosaccharides and are a substantial tool for fucoidan structural characterization [59]. It is noteworthy that S. chartarum was found to have fucoidanase and alginate lyases producing potential [60]