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NabajitKumarBorah, YuktiTripathi, AditiParashar,
SenehaSantoshi, andHinaBansal
Abstract
Aspergillus, a genus of lamentous fungi, showcases the intriguing interplay
between beauty and scientic complexity. Its diverse species, characterized by
their distinctive conidial heads resembling tiny paintbrushes, inhibits a wide
range of environments—from decaying organic matter to indoor spaces. Beyond
their aesthetic appeal, Aspergillus species are crucial players in biotechnology,
contributing to the production of enzymes, antibiotics, and organic acids. Yet,
this enchanting genus also poses health risks as opportunistic pathogens, empha-
sizing its dual role in the natural world and human well-being. This book chapter
provides an extensive exploration of saprophytic fungus, Aspergillus, and its
complex interactions with both human health and industrial applications. This
chapter delves into the diverse strains of Aspergillus and their wide-ranging uses
in industries, followed by a comprehensive analysis of the impact of Aspergillus
on human health, spanning from allergic bronchopulmonary aspergillosis to
invasive aspergillosis.
A signicant portion of this chapter is dedicated to the epidemiology of
Aspergillus-related diseases, elucidating the spectrum of diseases caused by this
fungus. The pathogenesis and host–pathogen interactions of Aspergillus are discussed in detail, shedding light on the mechanisms that enable the fungus to both
evade and combat host defenses.
N. K. Borah · Y. Tripathi · S. Santoshi (*) · H. Bansal (*)
Centre for Computational Biology and Bioinformatics, Amity Institute of Biotechnology,
Amity University, Noida, Uttar Pradesh, India
e-mail: ssantoshi@amity.edu
A. Parashar
Amity Institute of Microbiology Technology, Amity University, Noida, Uttar Pradesh, India
© The Author(s), under exclusive license to Springer Nature Singapore Pte
Ltd. 2024
S. Hameed, P. Vijayaraghavan (eds.), Recent Advances in Human Fungal
Diseases, https://doi.org/10.1007/978-981-97-4909-6_18
427
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N. K. Borah et al.
Of particular concern is the emergence of drug resistance in Aspergillus,
which is meticulously examined in terms of the mechanisms underlying antifungal drug resistance. The challenges associated with conventional antifungal
drugs are outlined, paving the way for an exploration of ongoing research in the
development of novel antifungal agents to combat resistance.
This chapter serves as a comprehensive guide understanding the intricate
dynamics of Aspergillus and its broad implications in various domains, encouraging innovative approaches to tackle the challenges posed by this versatile
microorganism.
Keywords
Epidemiology · Host–pathogen interactions · Invasive Aspergillosis · Antifungal therapy
Microbiology, biotechnology, and industrial fermentation have all paid signicant
attention to Aspergillus niger, a lamentous fungus of signicant biological and
industrial values. This research provides a comprehensive overview of the multiple
relevance of A. niger, highlighting its numerous ecological niches, genetic diversity,
and exible metabolic skills.
As a saprophytic decomposer, A. niger is essential to the recycling of organic
debris. Its widespread occurrence across a variety of environments highlights its
adaptability and ecological signicance. Due to its well-annotated genome and
genetic tractability, this fungus has also become a model organism for research
into the biology and genetics of fungal organisms (J Fungi (Basel), 2020 Dec).
Widespread usage of the universally accepted harmless organism Aspergillus
niger has occurred in the food business. To create mutants and to better understand the regulatory mechanisms of secondary metabolite production, traditional genome editing techniques must be used. Future investigation should
focus on developing A. niger strains using synthetic biology and metabolic engineering for particular industrial uses. A. niger can nevertheless induce a variety
of clinical problems while being less pathogenic than some other Aspergillus
species.
In the realm of drug discovery, computational drug design has become a crucial
aspect of research. Given A. niger’s biological and industrial importance, it is relevant to explore how computational techniques can aid in the evolution of novel
antifungal drugs. Through computational drug design, researchers can identify specic molecular targets within the A. niger fungus, such as unique proteins or metabolic pathways, which can be exploited to inhibit its growth or disrupt its vital
functions.
18 A Comprehensive and Intricate Dynamics of Aspergillus: Implications…
429
By leveraging computational simulations and bioinformatics tools, scientists can
screen a vast array of chemical compounds to identify potential drug candidates that
specically target A. niger while minimizing harm to human cells. This approach
not only accelerates the drug discovery process but also enables the development of
antifungal drugs with higher specicity and efcacy.
There is an abundance of strains of Aspergillus niger. Aspergillus niger strains vary
widely in length, ranging from 900 to 1600 μm for individual organisms, and
3–5μm for the rough, spherical conidia. In addition to being a species of plant
pathogen, Aspergillus niger is a group of 15 different Aspergillus varieties that are
all known to have black conidia (Aspergillus niger—bugwoodwiki 2014).
A. niger has many efcient strains which are currently used in various pharma-
ceutical processes of strains of niger (NRRL 3, NRRL 3122, and CBS 513.88,
ATCC 1015, ATCC 16404, DSM 821, etc (Cairns et al. 2018).
ATCC1015 and DSM 821 are widely used for their ability to produce a high
yield of citric acid and thus are extensively used for industrial purposes (Schäfer
etal. 2020).
Strong pectinolytic activity is one of the Aspergillus niger’s well-known traits.
However, although specialized strains for producing proteins or citric acid are wellcharacterized, the same cannot be said for strains that produce pectinases. Therefore,
employing controlled batch fermentation in stirred-tank fermenters, we thoroughly
examined the pectinase-related abilities of six A. niger strains (NRRL 3122, ATCC
11414,CBS 513.88, NRRL 3, N402, and ATCC 1015). The maximum polygalacturonase activity, particular protein production, and appropriate shape were demonstrated by A. niger ATCC 11414. Furthermore, when compared to the control lab
mutant A. niger N402, the release of D-GalA from sugar beetroot pulp was 75%
more. As a result, our research nds a base strain with high performance and suggests a robust initial selection of strain to direct the creation of next procedures for
the synthesis of -GalA from agricultural waste (Schäfer etal. 2020).
Aspergillus brasiliensis has had to be reclassied as the strain ATCC 16404 of
Aspergillus niger more recently. After additional investigation, it was determined
that this strain was too distinct to be recognized as a member of the same species,
necessitating a new classication in 2007 (Schäfer etal. 2020).
Mutations, the random alterations in DNA sequences, play a pivotal role in shaping
the evolution and survival of Aspergillus, a diverse genus of lamentous fungi.
These changes, while often imperceptible, can have profound consequences for the
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N. K. Borah et al.
organism’s ability to adapt to diverse environments, resist antifungal drugs, and
even become more pathogenic.
(a) Stress tolerance: Mutations can equip Aspergillus with resistance to harsh
environments. For example, mutations in genes such as hsp70 and sod1 enhance
tolerance to heat and oxidative stress, allowing Aspergillus to thrive in extreme
temperatures and oxidative environments (e.g., soil and compost) (Bayram
etal. 2016).
(b) Nutrient acquisition: Mutations can alter nutrient uptake and utilization. For
instance, mutations in genes such as nit3 and niaD enable Aspergillus to utilize
alternative nitrogen sources, adapting to nutrient-poor environments (Paoletti
etal. 2007).
(c) Cell wall composition: Mutations in genes related to cell wall biosynthesis can
modify cell wall structure, impacting stress tolerance and interactions with
hosts (e.g., plants).
(a) Azole resistance: Changes in the cyp51A gene, coding for the target enzyme
for azole antifungal drugs, are the most common system of resistance in
Aspergillus species (e.g., A. fumigatus) (Paul etal. 2017). These mutations alter
the enzyme’s structure, reducing its afnity for the drug and rendering the fungus less susceptible.
(b) Multidrug resistance: Multiple mutations in various genes can work together
to confer resistance to different antifungal classes, creating a more complex and
challenging resistance prole (Bösch etal. 2021).
(a) Toxins: Mutations can lead to the overexpression of genes encoding mycotox-
ins, potent secondary metabolites that damage host tissues and facilitate fungal
invasion (Bennett and Klich 2003).
(b) Immune evasion: Mutations can affect genes involved in immune evasion
strategies, allowing Aspergillus to evade host immune defenses and establish
infection (Poulsen et al. 2021; Bonugli-Santos etal. 2015).
(c) Tissue invasion: Mutations in genes encoding cell wall-degrading enzymes
can enhance Aspergillus’s ability to invade host tissues and disseminate
throughout the body (Lambou etal. 2024).
Point mutations: Single-nucleotide changes in DNA, often leading to amino acid
substitutions in proteins and altered protein function.
Deletions: Loss of a DNA segment, potentially leading to loss of gene function or
regulatory elements.
18 A Comprehensive and Intricate Dynamics of Aspergillus: Implications…
431
Insertions: Addition of DNA sequences, sometimes resulting in new gene functions
or disrupting existing ones.
Translocations: Movement of DNA segments between chromosomes, potentially
disrupting gene regulation or creating novel gene fusions.
Tawk etal. (2022) study investigated the use of sodium azide mutagenesis to modify Aspergillus niger, a common plant pathogen, and assess its impact on both fungal activity and host plant resistance.
Fungal Activity:
• Sodium azide inhibited spore germination, growth diameter, and mycotoxin production in A. niger, with increasing concentrations showing enhanced effects
(Schuster etal. 2002).
• Total protein and avonoid content of mutant fungi decreased compared to controls (Kumar and Parikh 2015).
• Genetic variation was observed in mutant A. niger using RAPD–PCR analysis,
indicating DNA instability and potential gene activation (Money 2016; Kumar
etal. 2014).
Plant Resistance:
• Maize and onion exhibited increased resistance to mutant A. niger compared to
controls, as evidenced by improved morphological and physiological parameters
(Mandeel 2005; Bacon etal. 2008).
Implications:
• Sodium azide mutagenesis can be a promising approach to reduce fungal pathogenicity and mycotoxin production.
• Enhanced plant resistance observed in maize and onion suggests the potential for
developing disease-resistant crop varieties.
• Further research is needed to optimize mutation protocols, analyze specic gene
modications, and evaluate the feasibility of applying this strategy in agricultural
settings.
To break down pectin and make use of the produced monomer (-galacturonic
acid), Aspergillus niger naturally secretes pectinases. The transcriptional activator
GaaR, the repressor of -galacturonic acid utilization, affects the transcriptional
regulation of -galacturonic acid genes, which includes the genes encoding pectinases (Alazi etal. 2018).
For many plants, Aspergillus niger is a severe pathogen. It plays a signicant role
in the deterioration, rotting, and breakdown of plant tissues. Mutations that lessen
A. niger’s harmful effects on plants can reduce the toxicity caused by the organism.
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N. K. Borah et al.
Using a molecular technique based on 18S rDNA, strains of A. niger were identied. A chemical mutagen called sodium azide (NaN3) inhibits the enzymatic activity of fungi and stimulates the synthesis of cellulose-degrading enzymes by
microorganisms, hence reducing the generation of mycotoxin. A. niger is treated
with varying amounts of sodium azide (30, 40, and 50μM).
One of the most effective chemical mutagens in several phytopathogens is
sodium azide (NaN3). It is employed, because it is easy to use, inexpensive, and
results in mutations that improve their traits. Azide concentration and duration of
treatment are two factors that affect how efciently mutants are produced. Plants
become resistant to a range of unfavorable circumstances as a result of point mutations and chromosome damage caused by it. In many animal and plant species,
sodium azide is cytotoxic at low levels, preventing the synthesis of proteins and
replicative DNA.Because it causes mutagenesis in bacteria, fungus, higher plants,
and human cells, it has been used as a positive control in a variety of systems (Tawk
etal. 2022).
Comparing, A. japonicus (14), Alternaria Alternata M7 (13), A. ustus M3s, and
the mold A. niger (wild type) and its mutants generated by UV irradiation showed
higher carboxymethyl cellulase and signicantly more activity of -glucosidase.
Therefore, it can be concluded that A. niger is the best suitable fungal species in
terms of the -glucosidase activity, which is really in charge of saccharifying cellulose (Helmi etal. 1991).
It has been observed that some strains of Aspergillus niger release ochratoxins,
which are mycotoxins that can cause nephrotoxicity and kidney tumors in a variety
of animal species. Ingestion of these strains may also increase a risk to human
health. Fungal species such as Aspergillus and Penicillium release them. For
instance, ochratoxin A is a problem organism, while storing grains in bulk if the
environment is humid or wet in any way (News-Medical 2018).
Aspergillus species infections result in considerable morbidity and mortality.
Seldom is Aspergillus niger mentioned as a potential cause of pneumonia. A middleaged female patient was undergoing long-term steroid treatment for chronic obstructive pulmonary disease (COPD), temporal arteritis, and hemoptysis when she
presented with pleuritic chest pain. The right upper lobe of the lung showed regions
of heterogeneous consolidation with cavitation on chest radiography. Acid-fast
smears and cultures, as well as induced bacterial sputum cultures, came up negative.
A. niger is grown in fungus sputum cultures. After receiving voriconazole alone for
a while and then empiric antibacterials in combination, the patient’s condition signicantly improved (Thompson and Young 2021; Person etal. 2010).
Globally, COPD is the third most common cause of mortality. It poses a serious
risk to health, well-being, and the economy for almost 500 million people, more
than 7% of the world’s population. Breathlessness, coughing, and sputum production are some of the persistent, incapacitating respiratory symptoms of COPD.Other
18 A Comprehensive and Intricate Dynamics of Aspergillus: Implications…
433
symptoms include systemic symptoms, such as weariness, muscular wasting, and
deconditioning (Otu etal. 2023).
Lung alveoli are accessible to Aspergillus conidia. Nonetheless, the immuno-
competent host’s innate immune system often eliminates these conidia quickly, preventing them from spreading illness. Patients undergoing transplants or those with
hematological malignancies are among the immune-compromised hosts most susceptible to invasive aspergillosis (IA). Aspergillus spores are less likely to be killed
by COPD patients’ airway defenses, and they have the ability to germinate despite
being killed by both professional phagocytes and epithelial cells. However, there
has recently been a greater focus on the signicance of Aspergillus in populations—
including COPD patients—that were previously thought to be at low risk of aspergillosis (Farazuddin et al. 2018; Otu etal. 2023).
Most cases of aspergillosis are caused by one of the common fungus, Aspergillus
fumigatus (AF), which has airborne conidia. The inhaled conidia are swiftly
removed in immunocompetent hosts. However, IA and the majority of Aspergillus
infections are particularly dangerous for immunocompromised or immunodecient hosts.
The rst site of host–fungus interaction is the lung epithelium. Its proactive func-
tion in host defense against A. fumigatus has been highlighted by recent research.
An opportunistic pathogen species Aspergillus niger is frequently discovered in
both indoor and outdoor settings. The spores of A. niger have the ability to enter
human respiratory tract bronchioles and are readily aerosolized. A. niger infections
can result in the development of IA or allergic bronchopulmonary aspergillosis
(ABPA), both of which have the potential to be fatal in-patient populations that are
vulnerable. Although sexual reproduction has been seen, Aspergillus niger normally
reproduces asexually. Typically, conidia, or spores, are discharged and spread by
wind in an asexual form. As hyphae germinate, conidia form. Aerial hyphae will
appear after hyphal colonization of the substrate, resulting in conidiophores, or
stalks, and conidial heads, which eventually form conidia.
This fungus spreads by the soil, water, and air. Typically, it is a saprophyte that
feeds on decomposing and dead materials. It is, therefore, frequently thought of as
a post-harvest illness. When the illness rst appears in both humans and animals,
there usually is a weakened immune system. Irrigation techniques that promote
disease development in plants include drip irrigation lines buried in the soil and hot,
humid growing environments. A genetic comparison of clinical and environmental
isolates from a range of host origins and geographic areas suggests that any environmental strain of Aspergillus may be pathogenic given a suitable host. Aspergillus
differs from other species in that it possesses a unique set of basic traits that contribute to pathogenicity.
Aspergillus is mostly transmitted by inhaling airborne conidia that deposit in the
alveolar spaces or bronchioles. Aspergillus conidia, which range in size from 2 to
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N. K. Borah et al.
3μm, are well-suited for deeply penetrating the alveoli, while A. niger conidia are
larger and may be more readily eliminated through mucociliary clearance of the
upper respiratory tract. According to a number of studies, pathogenicity and aspergilli’s radial growth and germination rate at 37°C are correlated (Dagenais and
Keller 2009).
The most frequent cause of fungal respiratory infections in immunocompro-
mised people is Aspergillus species. The relationship between the fungus and the
host determines the course of Aspergillus lung disease. In patients with impaired
immune systems, such as those undergoing immunotherapy, IA, the most severe
type of the disease, can develop. A weakened immune system can arise from various
situations, such as chemotherapy for cancer, immunosuppression following lung
transplantation to control graft versus host disease.
Innate and adaptive immunity make up the host’s defense mechanisms against
fungi. The two systems are tightly linked and controlled by sets of chemicals and
receptors to form a highly synchronized and cohesive process for defense against
fungal infections.
Asthma, cystic brosis (CF), and tuberculosis lesions are examples of pre-
existing pulmonary malfunctions where the immune system is weakened. A. fumig-
atus takes advantage of these vulnerabilities in the host defenses to cause saprophytic,
allergic, or IA.Conidia germinate and develop into invasive hyphae that have the
ability to enter pulmonary tissues if they are not successfully destroyed by the innate
immune response. A. fumigatus elicits a stage-specic innate immune response in
which the pathogen’s distinct cellular forms are met with the assistance of diverse
host defense mechanisms (Margalit and Kavanagh 2015).
Patients with weakened immune systems are at risk for IA, an infection brought
on by the opportunistic fungus AF.This condition is frequently linked to hematopoietic stem-cell transplants, organ transplants, cancer treatments, and specic
genetic changes. Fungal development is difcult to cure and causes signicant mortality rates. Innate immune deciencies include neutropenia and alveolar macrophage dysfunction. Noninvasive AF colonization is a possibility in other patient
groups with less severe or no patent immunosuppression at all. Among these patients
are those suffering from ABPA, CF, and COPD (Mackel and Steele 2019).
Although A. fumigatus’s cell wall is recognized by the host, it uses a variety of
immune evasion techniques to sustain its proliferation in the lung. It has been demonstrated that by preventing the immune system from identifying other cell surface
proteins, the cell wall protein CcpA boosts pathogenicity. A CcpA mutant was
found to exhibit elevated reactive oxygen species, inammatory cytokines, and epithelial damage invitro (Mackel and Steele 2019).
Epithelial defenses and other early actions after host exposure probably cause
many AF exposures to be cleared before germination. Many innate immune
responses identify AF and mediate clearance when germination does occur. Several