You’ve probably seen moldy bread or fruit covered in fuzzy grayish-white growths. That’s likely Rhizopus, a genus of fast-growing molds found everywhere in nature. While you may want to toss moldy food in the trash, Rhizopus is more than just a food spoiler. This ubiquitous fungus plays an important role in ecosystems and has many uses that impact our daily lives.
In this article, you’ll learn all about the characteristics of Rhizopus fungi, the different species, how they reproduce, and some of their surprisingly helpful applications, from fermenting foods to producing lifesaving drugs. Who knew such a common mold could be so fascinating? Read on to uncover the wonders of Rhizopus fungi.
What Is Rhizopus?
Rhizopus is a genus of saprophytic fungus that live on plants and are specialized parasites of animals. They can be found in a wide range of organic products, including “mature fruits and vegetables,” syrups, leather, bread, tobacco, and peanuts. They’re multicellular. Some Rhizopus species are opportunistic human pathogens that frequently cause the lethal disease called mucormycosis. This vast genus has at least eight species.
Rhizopus is a genus under the phylum Zygomycota. They are classified by the production of zygospores during sexual reproduction. They are found in soil, decaying organic matter like leaves, and plants. Rhizopus species are fast growing molds that produce cottony colonies. They reproduce through spores and have root-like filaments called rhizoids.
Rhizopus gets its name from the dark, root-like rhizoids. The rhizoids help anchor the fungus to the substrate and absorb nutrients. Rhizopus species are important decomposers in nature and some cause diseases in plants and humans. They have economic importance and are used to produce ethanol, fumaric acid, and other chemicals.
Characteristics of Rhizopus
Rhizopus has some distinctive characteristics, which include the following:
- It produces non-septate hyphae, meaning its hyphae lack cross walls. Its hyphae are also coenocytic, containing many nuclei not separated by walls.
- Rhizopus forms sporangiophores that produce sporangia containing haploid spores. The columella, a pillar-like structure in the center of the sporangium, bears the spores.
- Rhizopus is a saprophytic fungus, feeding on dead and decaying organic matter. It plays an important role as a decomposer in the environment.
- Rhizopus has a fast growth rate. Under ideal conditions, it can spread over large areas in a short time. Its hyphae move rapidly, up to 5mm per hour.
- Rhizopus reproduces sexually through zygospores and asexually by the formation of the spores. Its life cycle involves an alternation between haploid and diploid stages.
- Rhizopus possesses rhizoids that resemble roots and help anchor the fungus to its substrate. The rhizoids also absorb nutrients from the environment.
- Some Rhizopus species produce fumaric acid, which is important for the food industry. R. oligosporus is used in the commercial production of fumaric acid.
- Rhizopus causes opportunistic infections in humans called zygomycosis. Infection usually occurs through inhalation of spores and can be life-threatening if untreated.
- Rhizopus belongs to the phylum Zygomycota. It’s a common mold found all around the world, especially in tropical and subtropical regions.
Scientific classification of Rhizopus
Rhizopus belongs to the kingdom Fungi and the phylum Zygomycota. Its scientific classification is:
- Domain: Eukaryota
- Kingdom: Fungi
- Phylum: Zygomycota
- Class: Zygomycetes
- Order: Mucorales
- Family: Mucoraceae
- Genus: Rhizopus
Rhizopus are saprobic fungi in the family Mucoraceae. They are found worldwide in soil, decaying organic matter, and as pathogens of plants, animals, and humans. The genus Rhizopus contains several species, the most well-known species are Rhizopus stolonifer, Rhizopus arrhizus, and Rhizopus oryzae.
10 Major Species of Rhizopus
Eight major species of Rhizopus include:
- Rhizopus americanus
- Rhizopus oryzae
- Rhizopus stolonifer
- Rhizopus arrhizus
- Rhizopus azygosporus
- Rhizopus caespitosus
- Rhizopus circinans
- Rhizopus delemar
- Rhizopus homothallicus
- Rhizopus lyococcus
These species can be found worldwide and are commonly isolated from soil, decaying fruits and vegetables. Rhizopus species are opportunistic pathogens of plants, animals, and humans. They are a common cause of infection in immunocompromised individuals, resulting in mucormycosis. Treatment of Rhizopus infections is difficult and often requires surgery and antifungal drugs such as amphotericin B or posaconazole.
Despite their pathogenic potential, some Rhizopus species are important in industrial applications. Rhizopus oligosporus is used in the production of tempeh, a fermented soy-based food. Rhizopus stolonifer produces fumaric acid, an organic acid used as a food additive. Some Rhizopus species also show potential for biofuel production.
Overall, the genus Rhizopus contains species with important ecological, agricultural, industrial, and medical roles. Although some can act as pathogens, others provide benefits through food production, organic acid generation, and potential biofuel development. A better understanding of these fast-growing fungi will allow us to mitigate their detrimental effects and harness their useful properties.
Reproduction and Life Cycle of Rhizopus
Rhizopus reproduces through the production of spores, Sporangiospores. These spores are formed inside structures called sporangia. When the sporangia matures and bursts open, the spores are dispersed. If a spore lands in a suitable environment, it can germinate into a new Rhizopus organism.
The life cycle begins when a sporangiospore germinates and develops into a branching filamentous structure called a hypha. The hyphae grow and spread, eventually forming a thick mat of filaments called mycelium. When two compatible hyphae meet, they fuse together in a process called plasmogamy. The fused hyphae then undergo karyogamy, in which their nuclei fuse together. The resulting cell with fused nuclei is called a zygote. The zygote then develops into a sporangium in which new sporangiospores are formed, thus completing the cycle.
Rhizopus has a very short life cycle, allowing it to spread rapidly. Its asexual reproduction through sporangiospores is very efficient, producing large numbers of spores that can quickly populate an area under suitable environmental conditions. The ability to reproduce both sexually and asexually gives Rhizopus flexibility to adapt to different environments.
The structure of Rhizopus
Rhizopus is similar to cotton candy (also called candy floss or fairy floss) in texture. It has a mycelial structure, consisting of branched, thread-like hyphae. The hyphae has cross walls called septa, which divide the hyphae into separate cells containing multiple nuclei.
The vegetative hyphae absorb nutrients and help in anchorage and transport within the mycelium. Some hyphae fuse together to form thick strands called rhizoids that attach the fungus to surfaces.
Reproductive hyphae develop into sporangia that produce haploid spores. A sporangium has an oval shape and contains spores and columella in its center. The wall of the sporangium consists of two layers: an outer brittle layer and an inner flexible layer.
When the sporangium matures, the outer wall ruptures to release the spores. The spores are dispersed by wind and water, germinate under suitable conditions, and produce new hyphae to continue the life cycle.
In summary, Rhizopus has a simple structure consisting of hyphae, sporangia, and spores that enable reproduction, growth, and propagation. Proper understanding of its structural components helps in determining the characteristics and behavior of this fungus.
Uses of Rhizopus
These are some of the uses of Rhizopus:
Food Uses
Rhizopus species are used to produce tempeh, a fermented soybean cake that is a popular food in Indonesia. Rhizopus oligosporus is commonly used for tempeh production.
Industrial Uses
Rhizopus species are used industrially to produce fumaric acid, lactic acid, and lipases. Rhizopus arrhizus is used to produce fumaric acid which is used as a food acidulant. Rhizopus oryzae is used to produce lactic acid and lipases.
Traditional medicine
In traditional Chinese medicine, the fungus Rhizopus nigricans is used for conditions such as abdominal pain, diarrhea, and dysentery.
Biofuel production
Rhizopus species can produce bioethanol from rice straw and other agricultural wastes through simultaneous saccharification and fermentation. Rhizopus oryzae is commonly used for bioethanol production.
Rhizopus species have the potential for the production of biodiesel through microbial lipid accumulation and transesterification of the accumulated lipids.
Production of Enzymes
Rhizopus species are used for the production of enzymes such as amylases, cellulases, xylanases, and lipases which have applications in various industries. Rhizopus oryzae is commonly used for enzyme production.
Mushroom production
Some Rhizopus species such as Rhizopus stolonifer (black bread mold) can be cultivated as edible mushrooms. They are cultivated on waste materials such as rice straw, paper, and wood chips.
Decomposition
Some Rhizopus species act as decomposers in nature. They help in degrading waste materials such as rice straw, sugarcane bagasse, and wood chips.
Recycling Nutrients
The fungi absorb nutrients like nitrogen, phosphorus, and minerals from the decomposing matter. These are essential for plant growth. The nutrients are then released back to the soil when the fungi die or produce spores.
Food Source
Rhizopus serves as a food source for other organisms like insects, bacteria, and other fungi. Some animals also feed on the spores and mycelia of Rhizopus.
Production of Antibiotics
Some species of Rhizopus produce antibiotics that can be used in medicine. An example is rhizoxin, an antifungal and anticancer agent.
Fermentation
Rhizopus is used in the fermentation of foods like tempeh, soy sauce, and rice wine. The fungi help convert the carbohydrates in the foods into alcohols and organic acids.
Biocontrol Agent
Rhizopus species can be used as biocontrol agents against plant pathogenic fungi. They directly parasitize other fungi or produce antibiotics that inhibit their growth.
Model Organism
Rhizopus species like R. stolonifer are used as model organisms to study fungal genetics, biochemistry, and cell biology. They are easy to culture and have a short life cycle.
Frequently Asked Questions about Rhizopus
You probably have some questions about Rhizopus. Here are a few common ones:
Where can Rhizopus be found?
Rhizopus species are cosmopolitan, meaning they can be found almost anywhere, in soil, air, plants, rotting fruit and vegetables. The spores are dispersed through the air, allowing the fungus to spread widely.
Is Rhizopus harmful or friendly?
Rhizopus can act as both friend and foe. Some species are used commercially to produce fermented foods like tempeh or lactic acid. However, some Rhizopus species can also cause infection in humans, especially in immunocompromised individuals. Rhizopus stolonifer, also known as black bread mold, may lead to a disease called zygomycosis or mucormycosis.
How do you treat a Rhizopus infection?
A Rhizopus infection is serious and requires immediate medical attention. Treatment typically involves antifungal medications, surgery to remove infected tissue, and controlling any underlying conditions that made the person susceptible to infection. Untreated, mucormycosis can become life-threatening.
What is the economic importance of Rhizopus?
Some Rhizopus species are used commercially in the production of fermented foods like tempeh, soy sauce, and lactic acid. Rhizopus oligosporus is used to make tempeh, a meat substitute from Indonesia made from fermented soybeans. Rhizopus oryzae produces amylases and proteases used in the food industry. Some species also produce lipases, used in the production of biodiesel fuel.
How fast does Rhizopus grow?
Rhizopus grows very quickly. Under ideal conditions, its hyphae can spread several centimeters per day. Rhizopus reproduces through sporulation and can form spores within 6-8 hours.
Does Rhizopus need oxygen to grow?
Yes, Rhizopus is an obligate aerobe, meaning it requires oxygen to grow and thrive. Rhizopus respires aerobically, taking in oxygen and releasing carbon dioxide as it metabolizes nutrients. Without adequate oxygen, Rhizopus cannot germinate, sporulate or carry out metabolic functions.
How to identify Rhizopus?
Look for fast-growing, cottony colonies of fungi that are white, grey, or brown. Rhizopus produces sporangia that are round to oval in shape and contain many spores. The spores themselves are round, dark, and borne on the tips of sporangiophores.
What is the disease caused by Rhizopus?
Rhizopus commonly causes a disease known as rhizopus rot or bread mold. It infects stored fruits and vegetables, causing them to rot. It can also cause infections in humans known as zygomycosis or mucormycosis.
What is the use of Rhizopus in medicine?
Although Rhizopus itself can cause disease, some of the acids it produces may have medicinal uses. Rhizopus stolonifer produces fumaric acid, which is used to treat psoriasis. Rhizopus oryzae is used to produce lactic acid, citric acid, and lipase. It is also used to produce antibiotics.
What kills Rhizopus?
Both mononuclear and polymorphonuclear white cells of normal hosts kill Rhizopus by the generation of oxidative metabolites and cationic peptide defensins.
How can you prevent Rhizopus?
To avoid Rhizopus, keep humidity low and practice good hygiene. Disinfect damp areas with bleach and improve air circulation. Throw out old or spoiled food sources where the fungus can grow.
What antifungal is used for Rhizopus?
Common antifungals used to treat Rhizopus infections include amphotericin B, posaconazole, and itraconazole. These are available as oral medications or intravenous infusions for severe cases.
Is Rhizopus saprophytic or parasitic?
Rhizopus species are saprophytic fungi, meaning they feed on dead or decaying organic matter.
What is the habitat of a Rhizopus?
Rhizopus species are commonly found in environments rich in decaying vegetation, fruits, and plants. They inhabit soils, compost, and waste materials. Some Rhizopus species are also found as pathogens on plants, insects, and small animals.
Is it safe to eat Rhizopus?
Rhizopus species are not safe for human consumption and can cause serious health issues if ingested.
What does Rhizopus do to humans?
Rhizopus produces spores that can trigger allergic reactions and respiratory problems in humans. Rhizopus is also known to cause diseases in humans such as rhizopus infections, including rhizopus otitis, rhizopus keratitis, rhizopus pneumonia, and mucormycosis. Rhizopus infections are dangerous and can become lethal if left untreated. Rhizopus species release spores and chemicals that damage human cells and tissues.
What is the difference between fungus and Rhizopus?
Rhizopus is a genus of zygomycete fungi. So Rhizopus itself is a type of fungus. Fungi is a kingdom that includes molds, yeasts, mushrooms, and more. Rhizopus specifically refers to bread molds.
What is the difference between Rhizopus and spirogyra?
Rhizopus is a genus of filamentous fungi, whereas spirogyra is a genus of green algae. Rhizopus produces a network of dark filaments and reproduces using spores, while spirogyra has unbranched green filaments and reproduces by conjugation.
Is Rhizopus visible?
Yes, Rhizopus is visible to the naked eye. Its filamentous hyphae form cottony, wooly or furry colonies that often appear dark in color. The sporangia containing spores can also often be seen with the unaided eye, though higher magnification is needed to view the spores themselves.
Conclusion
Rhizopus might look a little weird under the microscope, but it’s an important part of many ecosystems and food chains. Next time you see some fuzzy black bread mold in your kitchen, take a closer look, it just might be Rhizopus! While this fungus can sometimes be a pest, overall it’s a fascinating microorganism that helps sustain life on our planet in many ways.