Aspergillus penicillioides facts for kids

Aspergillus penicillioides is a type of fungus that belongs to the Aspergillus family. It's known for being one of the most xerophilic fungi. This means it loves dry places and can grow even when there's very little water around.

You can often find Aspergillus penicillioides in the air inside buildings, in house dust, and on things that don't have much water. This includes dried food, old papers with foxing (brown spots), and even on objects like binocular lenses. This fungus is found all over the world. It has been discovered in bed dust from places with mild, Mediterranean, and tropical climates. The amount of this fungus depends on the outdoor weather. There's more of it in tropical areas and less in cooler places. Cold temperatures tend to reduce the number of A. penicillioides in house dust.

A new group of these fungi, called a colony, can start from a single spore. This can happen in slightly acidic conditions. The size of a colony can be tiny, less than a millimeter, or grow to several centimeters wide. It depends on what the fungus is growing on. A. penicillioides can start to grow (germinate) even in drier conditions than it needs to keep growing bigger. It can germinate in places with a water activity as low as 0.585.

What is Aspergillus penicillioides?

Aspergillus penicillioides is part of the Aspergillus group, specifically in a section called Restricti. Because it likes dry conditions, scientists like Charles Thom and Kenneth B. Raper first put Aspergillus restrictus into a special series within the Aspergillus glaucus group. Later, Raper and Fennell made this a separate group called "A. restrictus Group". Then, Helmut Gams and others renamed it Aspergillus Section Restricti.

Scientists have studied the family tree of A. penicillioides using its DNA. They found that A. penicillioides is closely related to A. restrictus, A. proliferans, and some other fungi like Eurotium and Edyuillia athecia. All these fungi share a similar chemical marker called Q-9.

How it Grows and Looks

Scientists have grown A. penicillioides in labs on special dishes called Czapek yeast extract agar (CYA) and yeast extract sucrose agar (YES). The pictures below show how the colonies look when they grow.

• 

  Aspergillus penicillioides growing on a CYA plate

• 

  Aspergillus penicillioides growing on a YES plate

A. penicillioides doesn't grow well, or at all, on a standard Czapek medium at 25–26 °C. It only reaches about 2 to 3 mm in size. But on Czapek's agar with 20% sucrose, colonies can grow to 1–1.5 cm in 4 weeks at room temperature. However, the fungus stays thin and doesn't produce many spores. It can produce more spores if it's grown at 33 °C.

On other types of dishes, like malt extract agar, it grows a bit faster. It forms tiny colonies and a few spore-producing structures. Sometimes, colonies can reach 5 mm across. On G25N agar, colonies can grow to 8–14 mm wide. They look wrinkled and fluffy. The color is dark green, and the underside is pale to dark green. On M40Y agar, colonies grow quickly, reaching 5 to 6 cm in 3 weeks. The fungus forms a thin, tough mat and produces spores in dark yellow-green shades. It can also grow as a green mycelium. The underside is colorless to greenish-brown or dark green, especially in the middle. It has a slight odor.

The spore-producing heads usually grow from the surface it's on, but some also grow from the fuzzy aerial parts of the fungus. When young, these heads spread out, then become column-shaped, about 80 to 90 μm wide. Spore heads from the aerial parts are smaller and become column-shaped faster. The stalks that hold the spores (conidiophores) are 150 to 300 μm long. They have thin, smooth, colorless walls. The tips of these stalks (vesicles) are mostly 10-20 μm wide and shaped like a pear. About two-thirds of the vesicle area produces spores, with structures called phialides that are 8-11 μm long. The spores (conidia) start as oval shapes and become round when they are ready. They are 4-5 μm wide and have spiny, blackish walls. This fungus does not produce perithecia.

History of Discovery

Aspergillus penicillioides was first named by Spegazzini in 1896. He found it on moldy sugarcane in Argentina. However, he didn't grow it in a lab. A specific sample, CBS 540.65, was later isolated from a human arm in Brazil. This sample was mistakenly thought to be a different infection.

The fungus has been found in many different places. For example, strain CBS 116.26 was found on sugar cane in Louisiana. Spegazzini confirmed it matched his original description. Strain CBS 539.65 was found on a gun firing mechanism, and CBS118.55 was isolated from a man in Netherlands. Other strains of A. penicillioides were found on dried fish from Indonesia in Australia, and on dried chili in Papua New Guinea. A sample called ATCC 16905, which was originally named Aspergillus vitricola, was found on a binocular lens in Japan by Torao Ohtsuki.

At one point, Aspergillus penicillioides was wrongly identified as the cause of a lung infection called aspergilloma. But later, it was found that the fungus in that case was actually A. fumigatus.

Fungus DNA

Scientists have found a lot of genetic differences among different samples of A. penicillioides. This suggests that some of these samples might actually be new species. When looking at the DNA, five strains of A. penicillioides were very similar to each other. However, A. penicillioides IFO 8155, which was first called A. vitricola, was quite different from the other five. This means IFO 8155 might not be A. penicillioides after all, and its original name A. vitricola might be used again.

The entire genome (all the DNA) of A. penicillioides was mapped in 2016. This was part of a big project to map the genomes of all Aspergillus species. The genome size for A. penicillioides was about 26.40 million base pairs.

How it Affects the Environment

Fungus and Dust Mites

Aspergillus penicillioides helps house dust mites, like Dermatophagoides pteronyssinus, to grow. In lab tests, mites that didn't have this fungus didn't do well. This shows that D. pteronyssinus mites need the fungus to survive. Mites grew faster when A. penicillioides was added to their food, along with things like yeast and wheat germs. This suggests the fungus is good food for the mites.

Specifically, A. penicillioides helps by breaking down dandruff, fats, and keratin, which are the main foods for mites. The fungus also provides its spores, vitamins B, and D to the mites.

However, A. penicillioides can also be bad for D. pteronyssinus. The balance between mites and fungi in a certain amount of food is important. If there's a lot of food available, the fungus can take it over faster than the mites. This is because fungi have a shorter life cycle and reproduce more quickly. This can slow down the mites' growth and even cause more of them to die. A. penicillioides can also change the texture of the food, making it harder for mites to move around and eat. Female mites are more affected by this because they need extra energy to produce eggs.

Damaging Things (Biodeterioration)

Aspergillus penicillioides is known to cause foxing (brown spots) on paper artwork and books. It was even found on brown spots on an ancient Egyptian painting in Tutankhamun's tomb. This discoloration can happen because the fungus produces colored pigments, or through chemical reactions in the paper. Treatments meant to stop fungus growth sometimes don't work.

Aspergillus penicillioides also caused mildew on cotton goods in Great Britain. It was rarely found on other damaged fabrics. This difference might be because of how the samples were collected. A type of mold found on cigars that looked gray-green was also thought to be A. penicillioides.

Health Effects

Aspergillus penicillioides is a common indoor fungus found in damp buildings. It has been linked to allergic rhinitis, which is like hay fever. If people are exposed to a lot of indoor fungus, there's a link between the amount of fungus and getting allergic rhinitis. Even though this fungus was first found in a skin infection, people are most likely to be affected by breathing it in. Things produced by mold growth, like certain gases and spores, can cause problems like allergies and asthma.

The continued growth of house dust mites helped by A. penicillioides can also be a health risk. Dust mites can trigger certain cells in our bodies, which then release chemicals that affect our breathing passages. This can make allergic reactions in the airways worse. However, there's some debate about how much A. penicillioides contributes to the allergies caused by Dermatophagoides pteronyssinus. Studies have shown that young mites without the fungus have similar allergy-causing chemicals as adult mites with the fungus.

Sick building syndrome, where the air quality in a building gets bad due to many things, including fungi, is a big public health concern. For example, A. penicillioides was found in all mattresses tested in Antwerp and Brussels.

There are ways to prevent and control A. penicillioides and its harmful effects. A fungal detector can tell you if a place is damp and might grow fungus. This allows you to take action before a big problem starts. The detector uses fungal spores to see how they react to the test site. If A. penicillioides shows a strong reaction at 71% relative humidity (like in dry areas of homes), it means it could contaminate that spot. A biosensor can also detect harmful gases like formaldehyde in the air. This biosensor works by seeing if the fungus's growth is stopped. It's cheaper than other methods but can't always identify the exact substance or its concentration. Other ways to prevent mold include controlling water leaks, managing condensation inside, and choosing materials that don't easily grow mold.

Food Contamination

Fungal infections can spoil stored cereals, seeds, fruits, nuts, cocoa beans, and raw sugar. This causes discoloration, loss of ability to grow (germinability), heating, a musty smell, and decay. This means the products are worth less and can even catch fire. For example, coffee made from moldy coffee beans loses its smell and taste. Seeds and nuts are used to make vegetable oils. However, A. penicillioides can increase the amount of free fatty acids in the oil, making it taste bad. The fungus growing on raw sugar can also change the sugar, reducing the good sucrose and increasing other sugars.

In 1955, Clyde Martin Christensen found that A. restrictus could grow on wheat even when it was very dry. Later, spores of A. penicillioides were found in processed wheat flour. These spores might get into grain from dust in the air during harvesting, storage, and processing. The presence of A. penicillioides can affect the quality, nutrition, and taste of bread.

Spores of A. penicillioides are also found where the filling meets the chocolate in chocolate truffles. The filling has enough water for the fungus to grow. The contamination might come from cocoa beans or from the air when the truffles are being coated.

Fungus as a Helper (Bioconversion)

2,4-Dichlorophenoxyacetic acid (2,4-D) is a common herbicide used to control weeds, but it has been reported to cause changes in DNA. A study showed that A. penicillioides can remove 2,4-D from liquid solutions. After a one-day delay, A. penicillioides removed 52% of the 2,4-D. This delay might be due to slow growth or the fungus needing time to produce specific chemicals to break down the pollutant. After most of the 2,4-D was gone, the fungus's ability to break it down slowed down.

Fungus Products (Metabolites)

A chemical called aurantiamide acetate has been found in Aspergillus penicillioides. This chemical can stop the action of certain enzymes called cathepsins. Cathepsin B and L are important in the breakdown of cartilage in joints, which happens in conditions like arthritis. So, this chemical from the fungus could potentially be used to develop treatments for cartilage problems.

Industrial Uses

Aspergillus penicillioides is used to treat wastewater from petrochemical factories. This wastewater contains short-chain fatty acids (SCFA) like acetic acid, propionic acid, and others. When Aspergillus penicillioides was grown in a special continuous flow reactor to treat this wastewater, it removed more than 75% of the chemical oxygen demand (COD) and over 80% of the SCFAs. This means it helped clean the water.