Zygomycota

Some fungi live in the dirt.

They grow on plants or bugs. They make tiny seeds to grow more. These seeds can sleep for a long time.

They wait for the right weather to wake up. Some fungi grow toward the light. This helps them spread their seeds far away. They can even help plants grow.

These tiny things are everywhere!

Zygomycota are a group of fungi. They live in soil or on dead plants and animals.

Most of these fungi are found on land. Some are parasites that live on insects or plants. Others help plants grow by working with them.

These fungi make tiny seeds called spores. They can make spores in two ways. One way is through asexual reproduction. This uses special parts called sporangia. These parts grow on stalks. The stalks grow toward the light to help spread the spores.

Some spores can sleep for a long time. They wait for the right temperature or food to grow.

Another way is through sexual reproduction. This makes a tough spore called a zygospore. To make one, two different fungal strands must meet. They use a chemical called trisporic acid to find each other.

The strands grow toward the chemical signal. They join together to build the zygospore. This spore has a thick wall to stay safe.

Zygomycota is a group of fungi that used to be a single division. Scientists now place these fungi into two different groups called Mucoromycota and Zoopagomycota. There are about 1,060 known species in this group. Most of these living things live on land in the soil. They often grow on decaying plants or animals.

Some species act as parasites on insects or small animals. Other members form helpful relationships with plants.

These fungi make spores to spread and grow. They can make spores in two different ways. In asexual reproduction, they build structures called mitosporangia. These are small containers that hold thousands of spores. The containers grow on stalks called mitosporangiophores. These stalks grow toward the light to help the spores spread. Some spores can also stay dormant, which means they sleep. They might wait for a few hours or many years. This sleep can be caused by the weather or the spore itself.

Sexual reproduction is a very special way these fungi work. To start, two different fungal strands must find each other. They use a chemical signal called trisporic acid to communicate.

The strands grow toward the signal until they touch. Once they meet, their walls stick together at a fusion septum. The tips of the strands swell up to form gametangia. These parts eventually join to create a tough zygospore.

Scientists have studied these fungi for a long time. An American scientist named Albert Francis Blakeslee discovered that some species need two different types to mate. He called these types (+) and (-). Later, Hans Burgeff found that these types use chemicals to find each other.

In 1964, researchers discovered trisporic acid as a metabolite. This chemical is what helps the fungi recognize a partner. This discovery helped people understand how sex hormones work in fungi.

Fungi have very interesting bodies. Most fungi use a material called chitin for their cell walls. Zygomycetes are different because they make chitosan instead.

This helps build their structure. The fungi also react to the world around them. They use light to decide which way to grow. This is called phototropism. They also feel gravity to know which way is down.

This helps them grow in the right direction to spread their spores.

Zygomycota, often called zygote fungi, was once considered a single division of the kingdom Fungi. Scientists now classify these organisms into two separate phyla: Mucoromycota and Zoopagomycota. There are approximately 1,060 known species within these groups. Most of these fungi are terrestrial, meaning they live on land. They are commonly found in soil or growing on decaying plant and animal matter.

Some species act as parasites on insects or small animals. Others form symbiotic relationships, which are helpful connections, with plants.

These fungi reproduce using spores, which are structures used for dispersal and growth. They can produce spores through both asexual and sexual means. Asexual reproduction involves mitospores, also called sporangiospores. These are produced in specialized containers called mitosporangia. These containers can hold anywhere from a few to several thousand spores. The mitosporangia are held up by stalks called mitosporangiophores. These stalks often show negative gravitropism, growing away from gravity, and positive phototropism, growing toward light. This helps the spores spread effectively. In some species, the spore walls contain sporopollenin, a substance made from beta-carotene that resists chemical and biological breakdown.

Another type of asexual spore is the chlamydospore. Unlike sporangiospores, chlamydospores are used for the persistence of the mycelium, which is the body of the fungus. They are released when the mycelium degrades. These spores have thick, pigmented cell walls and do not have a mechanism for dispersal. Zygomycetes can also enter a dormant state before germination. This dormancy can last from a few hours to many years. It can be exogenous, controlled by external factors like temperature, or endogenous, which depends on the internal metabolic features of the spore itself.

Sexual reproduction in zygomycetes is a complex process involving zygophores. These are aerial hyphae that act as sex organs. They come in two mating types, designated as (+) and (-). The opposite types grow toward each other using volatile pheromones, specifically trisporic acid. When the zygophores make contact, their walls adhere and flatten at a site called the fusion septum. The tips of the zygophores swell into structures called progametangia. A septum then develops to separate these gametangia from the base. The zygophore then becomes a suspensor. As the fusion septum dissolves, the cell wall thickens and develops warty structures. These warts eventually cover the entire cell to form a mature, resistant zygospore.

The study of these fungi has a rich history. The American mycologist Albert Francis Blakeslee discovered that some Mucorales species are heterothallic. This means they are self-sterile and require two different strains, (+) and (-), to initiate sexual activity. Hans Burgeff of the University of Goettingen later showed that this interaction happens because of low molecular weight substances diffusing through the environment. This was the first demonstration of sex hormone activity in any fungus. In 1964, trisporic acid was discovered as a metabolite in Blakeslea trispora. It was later identified as the hormone that triggers zygophore production in Mucor mucedo.

The cell walls of zygomycetes have a unique chemical structure. While most fungi use chitin, zygomycetes synthesize chitosan. Chitosan is a deacetylated homopolymer of chitin. To build these walls, specialized vesicles called chitosomes transport precursors and the enzyme chitin synthetase to the cell membrane. Through a process called exocytosis, the enzyme catalyzes bond formations using a sugar substrate. An enzyme called chitin deacetylase then cleaves the group to form chitosan polymer chains. These chains become microfibrils embedded in a matrix of proteins, lipids, and glucans.

Zygomycetes also interact deeply with light and gravity. Many species use phototropism to direct their growth. For example, the sporangiophores of Phycomyces grow toward light to help disperse spores. Some species, like Pilobolus crystallinus, use light to trigger their dispersal mechanisms. Light can also regulate metabolic pathways, such as the synthesis of beta-carotene. In contrast, light can sometimes inhibit sexual development in certain species like Phycomyces. Additionally, these fungi exhibit gravitropism, which is a growth movement in response to gravity.

This allows them to orient themselves correctly in their environment.