a. Higher order taxa
Fungi; Ascomycota; Eurotiomycetes; Eurotiales; Aspergillaceae
2. Description and significance
Aspergillus glaucus is a species of fungus that grows in hyphae, have conidial heads (1) and is characterized by smooth ascospores (2). A fungus with a wide environmental distribution that spans both the Arctic and urban soils, A. glaucus is a pathogen that rarely infects humans because of its high susceptibility to various antifungals (3). Its relative lack of mycotoxin production in many strains lowers the chance for human infections (4). However, as with other members of the Aspergillus genus, A. glaucus is capable of causing infections in immunosuppressed individuals (3). A case of A. glaucus infection is noted in a fatal instance of central nervous system aspergillosis which commonly includes symptoms of mental changes, seizures, and hemiparesis (5).
A. glaucus possesses specialized metabolic capabilities and a novel biosynthetic pathway that produces aspergiolide A, an anthraquinone derivative that is shown to reduce the growth of cancerous cells (6). Aspergiolide A is toxic against several cancerous cell lines including A549 (carcinomic lung cells) and HL60 (leukemia cells) (6). Further research on the pharmacological applications and drug development using aspergiolide A, as well as the efficacy of this secondary metabolite to destroy tumor cells, is conducted (7).
3. Genome structure
Unlike other species of Aspergillus, including A. niger, A. nidulans, A. fumigatus, and A. oryzae, A. glaucus lacks a complete genome sequence. However, genomic characteristics have been studied in relation to other halophilic characteristics and strains of A. glaucus have been shown to contain specific genes that are upregulated while under stress from high salt concentrations (8). Genes that code for the ribosomal protein AgRPS3aE, which is also found in halophilic yeasts, has been studied in relation to A. glaucus’ halophilic capabilities (9). These genes are capable of producing pharmacologically active metabolites, which would prove helpful in future biotechnology and molecular level research. However, these genes are coupled with low frequency of homologous recombination (8). Genome sequencing of A. glaucus may lag behind other species of Aspergillus due to this lack of homologous recombination and nonhomologous end joining pathway. These pathways allow double stranded DNA to be repaired when damaged. Further, without these pathways, targeted gene sequencing and replacement is difficult (8).
4. Cell structure
All Aspergillus species portray growth of yellow perithecia and develop walls that separate the sides of the cell during germination. More specifically, A. glaucus grows in multicellular filaments, or hyphae (2, Figure 1). The individual cells display uniseriate conidial heads that radiate outwards. The conidial heads are often green, blue, reddish, orange, or yellow (1, Figure 2). A. glaucus is characterized by smooth ascospores, typical of fungi classified as ascomycetes, ranging in size from 4.5-10.5 µm (2, Figure 2). These ascospores are a major identifier when differentiating between Aspergillus species.
5. Metabolic processes
Little is known about the metabolic processes specific to A. glaucus, but most Aspergillus species are defined as xerophilic and halophilic (1). Studies of the metabolic processes may be limited for the same reasons as genomic data, in that low frequency of DNA repair pathways makes A. glaucus fragile to work with and study. A. glaucus has been derived from saltern locations, indicating its extremely high NaCl metabolic capabilities (1). Both xerophilic and halophilic characteristics allow the fungus to reproduce in dry environments, specifically ones with extremely low water activity or colder temperatures. Growing in highly saline conditions would infer that A. glaucus uses a protection system to prevent detrimental loss of water through osmotic gradients. One way this is achieved is through synthesis of organic compounds that are stored in the cytoplasm. Metabolic toxicity of A. glaucus is noted and a result of two metabolites that it produces, kotanin and desmethylkotanin (10).
A. glaucus has worldwide geographic distribution from Arctic marine environments to urban areas to plant materials and soil (1). It is well adapted to environments that are dry, have high sugar concentrations, and have high salt concentrations. It grows optimally at temperatures below 35℃, and is thus used in research focusing on enzymes and cellular structures that function at low temperatures (11). A. glaucus has many applications in the study of pigment formation, human infection, and other enzymes that break down sugars (12). Most importantly, it produces the mycotoxin aspergiolide A which is a potential and powerful anti-tumor compound (7).
Generally, A. glaucus is not considered to be a very invasive species of fungus and is rarely encountered in clinical laboratories. However, several strains of A. glaucus have been known to produce and release mycotoxins, a class of fungal chemicals that are capable of causing infections. For instance, A. glaucus has been implicated as the cause of ocular infections, especially after traumatic injury to a particular region of the body (5). These ocular infections can range from benign to severe, causing symptoms including ocular discharge, visual impairment, or red and painful eyes. Treatment for ocular infections can also range from mild to aggressive, depending on the severity of the infection and what part of the eye is infected (13). There have also been other types of infections associated with A. glaucus including cerebral, orofacial, cardiovascular, pulmonary, nasal and ear infections, although these are rare. There has only been one recorded instance of an infection caused by A. glaucus that resulted in a fatality. An otherwise healthy and immunocompetent adult contracted a brain infection caused by A. glaucus, which ultimately led to his death despite aggressive antifungal treatments (5).
8. Current Research
Current A. glaucus research involves the continuing effort to further understand the mycotoxin aspergiolide A that has potential benefit in cancer study (6). The biosynthetic pathway of aspergiolide A production has been determined (7). Further, novel methods of enhancing the production of the antitumor compound, along with other compounds with potential human health benefit, have been developed (14, 15). Along with developing aspergiolide A production methods, the effects that this mycotoxin has on the growth and sexual development of the fungus itself are also being explored in an attempt to better understand fungal physiology (16). Recent studies have focused on the enzyme b-1,4-glucosidase, and other enzymes like it produced by A. glaucus, to break down polysaccharides and starches (17, 18). Another recent study tested A. glaucus resistance to abiotic environmental conditions and explored the function of the ribosomal protein RPL44 which conferred such resistances (19). To better understand the genome of A. glaucus, improvements have been made in gene targeting procedures and sequencing methods as well (8).
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