The term spore is derived from the ancient Greek word spora, which means seed and sow. In layman's terms, the difference between "spore" and "gamete" is that the spore will germinate and become a spore, and the gamete must combine with another gamete to form a zygote for further development. Spores germinate to produce haploid gametophytes, while seeds germinate to produce diploid sporophytes.
The main difference between a spore and a seed as a dispersal unit is that the spore is unicellular and is the first cell of the gametophyte, while the seed contains a developing embryo that is the next generation of the multicellular sporophyte, which is composed of the pollen tube produced by the fusion of the male gametophyte of the gametophyte contains the female gamete formed by the giant gametophyte in the ovule.
We will learn more about what is a bacterial spore and what is the meaning of spores.
Here we will learn in brief about what are spores. Spore biology is a sexual or asexual reproductive unit that can adapt to spread and survive, usually for a prolonged period of time under adverse conditions. Spores are part of the life cycle of many plants, algae, fungi, and protozoa. Bacterial spores are not part of the sexual cycle, but rather a resistant structure to survive in adverse conditions. Mythimna spores release the amoeba into the host for parasitic infection, but also reproduce in the host by pairing two nuclei in the amoeba-developed plasmodia.
The spores are usually haploid and unicellular, produced by meiosis in the sporangia of diploid sporophytes. Under favourable conditions, spores can develop into new organisms through mitosis, produce multicellular gametophytes, and eventually continue to produce gametes. The two gametes fuse to form a zygote and the zygote becomes a new sporophyte. This cycle is known as alternation of generation. Seed plant spores are produced internally. Megaspores are formed in the ovule and microspores participate in the formation of more complex structures, forming dispersed units, seeds, and pollen grains.
Classification of Spore-producing Organisms
Spore biology is not produced by animals. They are mainly produced by plants, fungi, and bacteria.
Vascular plant spores are always haploid. Vascular plants are homosporous or isospora or heterosporous. Homosporous plants produce spores of the same size and type. Heterosporous plants, such as seed plants, spike moss, Stipa, and Salviniales ferns produce spores of two different sizes. The larger spores are megaspores that actually act as female spores, and the smaller ones the microspores are used as male spores. These plants usually produce two types of spores from a single sporangium, that is, the megasporangium that produces megaspores of the microsporangium that produces microspores. In flowering plants, these sporangia appear on carpels and anthers, respectively.
Fungi generally reproduce sexually or asexually to produce spores. The spores are usually haploid and develop into mature haploid individuals through mitosis. The spores and teliospores of rust are binuclear. Binuclear cells are formed by the fusion of two haploid gamete cells. In sporulating binuclear cells, nuclear ligands the fusion of two haploid nuclei occurs to produce diploid cells. Diploid cells undergo meiosis to produce haploid spores.
After understanding what is the meaning of spores, we will now learn about their external anatomy. Under high magnification, the outer surface of the spore usually has complex patterns or decorations. Special terminology has been developed to describe the characteristics of these modes. Some marks represent openings, which are places where the tough shell of the spore can penetrate during germination. Spores can be classified based on the location and number of these marks and holes. Alete spores do not have lines. In mononuclear spores, there is a thin line on the spore.
This indicates that the mother spore divides into four along the vertical axis. In triple spores, each spore shows three narrow lines radiating from the central pole. This indicates that the four spores share a common origin, initially contacting each other to form a tetrahedron. A wider slot-shaped hole can be called a spiral. The number of colpus distinguishes the main flora. Eudicots have trisporum spores, spores with three colpus.
In fungi, the asexual and sexual spores or sporangia of many species of fungi are actively dispersed by forcible expulsion from their reproductive structures. This spray ensures that the spores are expelled from the reproductive structure and spread over great distances in the air. Therefore, many fungi have specialized mechanical and physiological mechanisms and spore surface structures for the expulsion of spores, such as hydrophobins. These mechanisms include, for example, the forced expulsion of ascospores through the structure of the ascus and the accumulation of penetrant in the fluid of the ascus, resulting in the explosive release of ascospores into the air.
The forced discharge of individual spores called ballistic spores involves the formation of small water droplets, which when in contact with the spores cause the release of their projectiles. Other fungi depend on alternative mechanisms for the release of spores, such as external mechanical forces, such as the puffball. Attracting insects such as flies to get attracted to the fruit structure, with its bright colour and rotten smell, spreading fungal spores is another strategy, the most prominent being the smelly horns.
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Here, we will learn about what is a bacterial spore. Endospores are inactive, resistant, and non-reproductive structures produced by some bacteria of the phylum Firmicutes. The name endospore implies a form of spore or seed, but it is not a true spore. It is a simplified form of inactivity, and bacteria can restore themselves to this form. Endospore formation is generally triggered by a lack of nutrients and generally occurs in Gram-positive bacteria. In the formation of endospores, the bacteria divide within their cell walls and are then swallowed by the other side. Endospores allow bacteria to remain inactive for long periods of time, even centuries.
There are many reports of spores alive for more than 10,000 years, and it is claimed that the spores were resurrected millions of years ago. There are reports of viable spores of Bacillus marismortui in salt crystals dating back about 250 million years. When the environment becomes more favourable, endospores can be reactivated into a vegetative state. Most types of bacteria cannot become endospores. Examples of bacterial species that can form endospores include Bacillus cereus, Bacillus anthracis, Bacillus thuringiensis, Clostridium botulinum, and Clostridium tetani.
After learning about what is a bacterial spore, we will understand its composition. The endospores are composed of bacterial DNA, ribosomes, and a large amount of dipicolinic acid. Dipicolinic acid is a spore-specific chemical that seems to contribute to the ability of endospores to stay dormant. This chemical accounts for 10% of the dry weight of the spores. Endospores can survive without nutrients. They are resistant to ultraviolet radiation, dryness, high temperature, extreme freezing, and chemical disinfectants.
Ferdinand Cohn assumed heat-resistant endospores after studying the growth of Bacillus subtilis in cheese after boiling. His view that spores are the reproductive mechanism of growth is a major blow to earlier suggestions about spontaneous generation. Endospores are usually found in soil and water, where they can survive for a long time. Many different microorganisms form spores or cysts, but the endospores of low gram-positive bacteria are the most resistant to adverse conditions.
Bacterial Spore Structure
Bacteria produce a single endospore within them. The spores are sometimes surrounded by thin layers called exospores, which cover the outer layer of the spores. The spore layer is like a sieve, which can exclude large toxic molecules such as lysozyme, and is resistant to many toxic molecules, and can also contain enzymes involved in germination. In Bacillus subtilis endospores, the spore layer is estimated to contain more than 70 coat proteins, which are organized into inner and outer layer layers. The X-ray diffraction pattern of the purified Bacillus subtilis endospores showed that there are components with regular periodic structure, and Kadota and Iijima speculated that it could be made up of keratin-like proteins.
The bacillus subtilis genome was sequenced and no human keratin orthologs were detected. The cortex is located below the spore layer and consists of peptidoglycan. The nucleus wall is located under the cortex and surrounds the nucleus of the protoplast or endospore. The nucleus contains the chromosomal DNA of the spore, which is wrapped in a chromatin-like protein called SASP, which protects the DNA of the spore from ultraviolet radiation and heat because it is an acid-soluble protein. The nucleus also contains normal cellular structures, such as ribosomes and other enzymes, but it has no metabolic activity. Up to 20% of the dry weight of endospores is composed of calcium dipicolinate in the nucleus, which is believed to stabilize DNA.
Dipicolinic acid may be responsible for the heat resistance of spores, and calcium helps heat resistance and antioxidants. However, mutants that are heat resistant but lack dipicolinic acid have been isolated, indicating that other mechanisms that contribute to heat resistance are also at work. Small acid-soluble protein (SASP) is present in endospores. These proteins tightly bind and condense DNA, and are partly responsible for resisting ultraviolet rays and chemicals that damage DNA. So, this paragraph helps us to understand what is the meaning of spore structure.
Formation and Destruction of Bacterial Spore
Here we will learn about spore formation definition. Under starvation conditions, especially when carbon and nitrogen sources are lacking, some bacteria will form a single endospore through a process called sporulation. When the bacterium detects that environmental conditions have become unfavourable, it can initiate the endospore formation process, which lasts about eight hours. The DNA replicates and begins to form a membrane wall called the spore septum between it and the rest of the cell. The plasma membrane of the cell surrounds this wall and ruptures to leave a double membrane around the DNA. This developing structure is now called a prespore.
During this period, calcium dipicolinate or calcium salt of dipicolinic acid was incorporated into the spores. Dipicolinic acid helps stabilize the protein and DNA in endospores. Then a peptidoglycan shell is formed between the two layers, and the bacteria adds a layer of spores outside the spores. In the final stage of endospore formation, the newly formed endospores are dehydrated and mature before being released from the stem cells. The crust is to withstand the temperature. The cortex comprises an intimal membrane known as the nucleus. The internal membrane surrounding this nucleus leads to the resistance to ultraviolet rays and hostile chemicals that generally destroy microorganisms. Spore formation is completed and ripe colin rocks are released when surrounding nutritional cells degrade. The internal stimulus is usually resistant to most medications that are generally killed by nutritional cells formed.
However, sterile alkylating agents, such as ethylene oxide and 10% whitening agent are effective against domestic vessels. To kill most anthrax spores, standard household whitening including 10% sodium hypochlorite must be in contact with the spore for at least several minutes. Such a solution can survive very small volumes of spores for more than 10 minutes. The highest concentration of bleach is not more effective, and some types of aggregate bacteria, therefore, can survive.
Although it is significantly resistant to heat and radiation, the household can be destroyed at temperatures greater than hundred-degree celsius at temperatures above or above the boiling point of water. An indirect way of destroying them is to place them in an environment where they reactivate them to nutritional conditions. Germinate within a day or two days with the correct environmental conditions, and the nutritional cells are not stronger, but they can break directly. This indirect form is called Tyndallation.