Aspergillus niger is one of the most common species from the Aspergillus genus which includes over 200 different species. A. niger is part of the section Nigri, having black conidial heads. A. niger is now known as A. brasiliensis as of 2010 but has yet to catch on other than the ATCC catalogue.
Aspergillus Niger is one of the 36 species of molds genetically identified in an index called ERMI that is an acronym for Environmental Relative Moldiness Index that uses qualitative and quantitative PCR (qPCR) analyses for fungi. PCR is basically the identification of mold species by DNA sequencing. More information on ERMI testing.
Typical Areas Found
A. niger is cosmopolitan and of very common occurrence. It grows aerobically on organic matter.
This species is a common contaminant on various substrates mainly found in soil and litter, in compost and on decaying plant material. It can even be found in icy and marine environments, but usually prefers dry and warm soils.
It is often isolated from house dust, soil, dried nuts, fruits and seeds as well as various types of untreated textile materials such as jute hemp and cotton bracts; hence, the often abundant presence of this species in the textile industry. A. niger can also contaminate meat and eggs, causing progressive spoilage. Spices and sun-dried fruit may also contain A. niger.
Even though it is considered an ubiquitous innocuous contaminant, Aspergillus niger can, in special rare circumstances, cause opportunistic human diseases.
A. niger is a mesophilic fungus: its optimal growth temperature is 20-40 °C, with good growth at 37 °C. It can survive at 60 °C but, for example in fruit juices, can be killed by exposure at 63 °C for 25 minutes.
This species is xerophilic and requires a minimal Aw (available water) of 0.77. This explains why A. niger is one of the most common Aspergillus species and is typically responsible for post-harvest decay of fresh fruit and is frequently isolated from nuts and sun-dried products. The species can, however, grow very well within an environment of 90-100% relative humidity. For the production of the mycotoxin ochratoxin A, an Aw of at least 0.92-0.94 would be required. It can also grow at very acidic environments down to a pH of 2.0.
Aspergillus niger is prevalent in residential areas, even in urban settings, and is recovered in both indoor and outdoor air samples. A. niger can be found growing on damp building materials and in contaminated ventilation systems. It is also found as an airborne contaminant of many buildings processing vegetable matter or producing commercially A. niger metabolites.
Mycotoxins Produced by Aspergillus niger
There is recent evidence that suggests some true A. niger strains do produce Ochratoxin A and Gliotoxin. It also produces the isoflavone orobol under favourable conditions that include temperature, humidity, and type of substrate. Other mycotoxins that Aspergillus niger produces include Malformins B & C, Naphtho-gamma-pyrones, and Oxalic acid.
Aspergillus niger is less likely to cause human disease than some other Aspergillus species. It is considered allergenic. In extremely rare instances, humans may become ill, but this is due to a serious lung disease, aspergillosis, that can occur. Aspergillosis is, in particular, frequent among horticultural workers who inhale peat dust, which can be rich in Aspergillus spores. Aspergillosis typically requires the inhalation of high concentrations of spores over a relatively long duration in months to years.
Aspergillus niger is one of the most common causes of otomycosis (fungal ear infections), which can cause pain, temporary hearing loss, and, in severe cases, damage to the ear canal and tympanic membrane.
With a high enough mean concentration, A. niger is believed to disrupt the immunity of pneumonia, eye infections, invasive lung, heart, and other diseases.