Botany - B.E. Yakubenko 2017

Part Two. System of the Organic World
Chapter V. System of the Organic World
5.2. KINGDOM MONERA

This kingdom comprises two domains: Bacteria and blue-green Algae. The defining feature of these organisms is the absence of a true nucleus.

Class="center">5.2.1. Domain Bacteria (Bacteriophyta)

Bacteria are single-celled, anuclear (prokaryotic) heterotrophic or autotrophic microorganisms that represent the most ancient life forms on our planet. Their fossil remains date back to the Archean eon. Bacteria were discovered by the Dutch researcher A. van Leeuwenhoek in the late 17th century. Later, in the mid-19th century, significant contributions to bacteriology were made by the French scientist L. Pasteur, regarded as the founding father of microbiology, the German scientist R. Koch, and the Russian scientists M. Teryokhovsky and I. Mechnikov (late 19th to early 20th century).

Distribution of bacteria. Bacteria are widespread across diverse environments: soil, Water, air, On the surface and inside the Organs of plants, animals, and humans, as well as on various inanimate objects. They thrive in hot springs with temperatures up to 100 ^оС, in the craters of dormant volcanoes, and survive in the vacuum of space and deep within ice sheets. Bacteria can withstand high salinity, and are found deep within the Earth's crust, in marine trenches at depths of 11 km, and in the atmosphere at altitudes of 41 km. Unlike aerobic bacteria, which require oxygen to live, anaerobic bacteria can thrive in oxygen-free environments. Bacteria are generally less tolerant of acidic environments.

The bacterial Cell has a Structure typical of prokaryotes. Externally, it is enclosed by a Cell wall and a mucous capsule, which provides additional cellular protection and participates in water exchange. Most commonly, the capsule consists of Polysaccharides with admixtures of Glycoproteins and Peptides.

The Cell wall is rigid and composed of peptidoglycan (murein)—a polysaccharide whose monomers are amino sugars forming a peptide chain of 4—5 amino acid residues. Beneath the cell wall lies the Cytoplasm, which contains an outer lipoprotein membrane that regulates METABOLISM. This membrane forms invaginations known as mesosomes and thylakoids. Certain types of mesosomes are separated from the cytoplasm by their own membranes and perform the Functions of Mitochondria and the Golgi apparatus. Thylakoids form the photosynthetic apparatus in phototrophic bacteria. The unstructured region of the cytoplasm, or matrix, contains Ribosomes, membranous structures, and reserve nutrients such as starch, Glycogen, oil droplets, and volutin (polyphosphate), which serves as an energy source. Also located in the matrix is the nucleoid—the functional equivalent of a nucleus, represented by a circular DNA molecule—along with extrachromosomal DNA segments known as Plasmids. Some bacterial Cells possess locomotory organs called flagella.

Bacterial Nutrition. Bacteria exhibit the following Nutritional types: heterotrophic, phototrophic, chemotrophic, and symbiotic. Heterotrophic nutrition is the predominant type. Among heterotrophic bacteria, Saprophytes stand out as they utilize the organic remains of dead plants and animals. These include putrefactive and fermentative bacteria. Putrefaction is the process by which bacteria decompose nitrogenous compounds, accompanied by the release of ammonia, hydrogen sulfide, and other gases. Fermentation is The breakdown of sugar-rich compounds by bacteria. Distinctions are made among lactic acid, butyric acid, acetic acid, and pectin fermentations. Lactic acid bacteria are utilized in the dairy industry, acetic acid bacteria in vinegar production, and pectin-fermenting bacteria in the pickling and fermentation of vegetables and fruits. Saprophytic bacteria, together with Fungi, promote the Mineralization of organic residues and drive the global cycling of elements.

Heterotrophic bacteria that colonize Living organisms are referred to as parasites; they cause diseases in plants, animals, and humans.

Phototrophic nutrition (photoreduction, or Bacterial Photosynthesis) is characteristic primarily of a small group of aquatic green and purple bacteria that contain the green pigment bacteriochlorophyll.

Chemotrophic bacteria synthesize organic substances by utilizing The energy released during The oxidation of mineral compounds. These include nitrifying bacteria, sulfur bacteria, iron bacteria, and hydrogen bacteria.

Symbiotic bacteria, commonly known as rhizobia or ROOT-nodule bacteria, are capable of fixing atmospheric nitrogen by colonizing the roots of legumes and other plants.

Shape of bacterial cells. Bacterial cells vary greatly in shape, which can be categorized into the following types: spherical, or cocci; rod-shaped, or bacilli; comma-shaped, or vibrios; and twisted, or spirilla and spirochetes. When cocci occur in pairs, they are called diplococci; if arranged in chains, streptococci; and in grape-like clusters, staphylococci. Spirilla are rigid spiral rods with 1—3 turns, whereas spirochetes are highly flexible, slender, wavy cells with a greater number of turns. Some bacteria may exhibit star-shaped, worm-like, or branched coral-like forms.

A characteristic feature of bacteria is their ability to form structures that differ significantly from their vegetative forms. These morphologically differentiated structures include specialized cells such as endospores, or resting cells, which form inside the mother cell and are released upon the breakdown of its wall. Their function is not reproduction, but survival under adverse environmental conditions.

Exospores form on The surface of the mother cell and subsequently detach from it, serving as diaspores for vegetative propagation.

Cysts are resting spores with a thick, rigid wall that enables them to endure unfavorable conditions. Upon the return of favorable conditions, the cyst sheds its wall and the cell resumes division.

Bacteroids are branched forms of root-nodule bacteria that develop during the Formation of Plant root nodules.

Reproduction of bacteria. Bacteria most commonly reproduce through Cell Division. Under favorable conditions, each mother cell produces two daughter cells within 20 min; if a single bacterial cell enters The Human Body, its population can reach several billion within 15 hrs. In some bacteria, such as Escherichia coli, a process of conjugation may occur. In the absence of a true sexual process, genetic Variability in bacteria is ensured through genetic recombination, which involves The transfer of a DNA segment from one cell to another. The pathways of recombination include:

- conjugation — exchange of DNA fragments through direct cell-to-cell contact;

- Transduction — transfer of DNA mediated by Bacteriophages;

- transformation — uptake of naked DNA from the surrounding environment;

- plasmids — exchange of extrachromosomal DNA segments between cells.

The Role of bacteria in the biosphere and human life. Soil saprophytic bacteria break down organic matter, mineralizing it and driving the biogeochemical cycles of elements in nature, including compounds of nitrogen, iron, sulfur, and carbon. Other bacteria fix atmospheric nitrogen, converting it into a form accessible to plants. By decomposing dead organic remains, bacteria release carbon dioxide, which is essential for plant photosynthesis. Chemosynthetic bacteria are believed to have played a leading role in The formation of petroleum, as well as deposits of iron and sulfur ores.

A numerous group of symbiotic bacteria inhabits the human gut, playing a vital role in Digestion, synthesizing certain Vitamins, and preventing the colonization of pathogenic organisms. In the stomachs of ruminant animals, bacteria facilitate the digestion of Cellulose.

Parasitic bacteria cause a wide range of plant diseases known as bacterioses. They attack all plant organs, causing rots, tumors, spotting, and other pathologies. When pathogenic bacteria invade the human body, they cause prevalent diseases such as diphtheria, tuberculosis, sore throat (tonsillitis), cholera, typhoid fever, dysentery, Gonorrhea, and Syphilis, among others. In animals, they cause anthrax and brucellosis, among other infections.

Under favorable conditions, bacteria multiply rapidly and can trigger epidemics. Preventive measures against infectious bacterial diseases include adherence to Sanitary and hygienic standards, vaccination, isolation of infected individuals or animals, and quarantine.

Bacteria have long been used in human economic activities. For instance, lactic acid and acetic acid bacteria are employed to produce kefir, cheeses, sour cream, yogurts, and acetic acid. Certain groups of bacteria are utilized in the microbiological industry to obtain Antibiotics, vitamins, Enzymes, and other Pharmaceuticals, as well as feed concentrates for animal supplementation. Bacteria are also harnessed to create specialized agents for controlling agricultural and forest pests. Furthermore, they play a role in leather tanning, silage fermentation, pickling vegetables and fruits, and extracting fibers from flax and hemp.

Under improper storage conditions, some bacteria cause food and feed spoilage, and consuming spoiled products can lead to food poisoning or even death. For example, the anaerobic bacterium that thrives in improperly canned meat, mushrooms, or fish causes a disease known as botulism; if prompt medical assistance is not provided, a person can die within a day. Pathogenic bacteria can be considered a type of biological weapon, which is why their production and stockpiling are prohibited by international conventions.

Self-Assessment Questions

1. What is The structure of a bacterial cell?

2. How does the nucleoid differ from a true nucleus?

3. Name the shapes of bacterial cells.

4. How do bacteria reproduce?

5. Where are bacteria distributed?

6. Name the classes of bacteria.

7. What natural processes are caused by saprophytic bacteria?

8. Name all the modes of nutrition in bacteria.

9. What human diseases are caused by bacteria?

10. What is the role of bacteria in the biosphere?

11. What is The Significance of bacteria in human life?

5.2.2. Division Blue-Green Algae (Cyanophyta)

Blue-green algae, much like bacteria, represent a rather ancient group of autotrophic organisms. Their age on Earth is estimated at about 3.5 billion years. They differ from other algae by lacking a true nucleus, which aligns them closely with bacteria; consequently, in some taxonomic systems, they are classified as a class of bacteria.

Cell Structure. The cells are mostly spherical or cylindrical, enclosed by a two-layered wall. The outer layer consists of pectic substances and microfibrils, while the inner layer is made of murein. In most species, a mucous sheath or colonial slime, consisting primarily of pectic substances, forms over the cell wall. The cytoplasm is enclosed by The Plasma Membrane (Plasmalemma), which, similarly to bacterial cells, forms various folds, notably thylakoids. Even under a Light Microscope, two distinct layers are visible in the protoplast: the outer pigmented layer, the chromatoplasm, and the inner colorless layer, the centroplasm. The chromatoplasm contains thylakoids bearing pigments: chlorophylls, carotenoids, blue pigments—phycocyanins (phycocyanin, allophycocyanin, phycoerythrocyanin)—and the red pigment phycoerythrin. Altogether, there are more than 30 pigments, and the ratio among them determines the color of the chromatoplasm and the cell. The centroplasm houses the nucleoid, which differs from a typical nucleus by the absence of a nuclear envelope and nucleoli. The centroplasm also contains ribosomes, inclusions, and gas vacuoles, which act as a kind of "swimming bladder".

The products of photosynthesis in blue-green algae include a glycogen-like polysaccharide, volutin, and cyanophycin.

Blue-green algae are unicellular, colonial, or Multicellular Organisms. Unicellular and filamentous algae can form colonies. Filamentous algae can be homocystous, consisting of identical cells, or heterocystous, where the filament comprises both vegetative cells and heterocysts. Heterocysts are located singly within the filament and differ from vegetative cells by their colorless content and double wall. The section of a colony located between two heterocysts is called a hormogonium. Heterocysts perform the function of atmospheric Nitrogen Fixation.

Blue-green algae reproduce asexually: unicellular forms by cell division, while colonial and filamentous forms reproduce via fragmentation of the colony or filament. A primitive parasexual process, which involves the partial fusion of genomes from different cells, occurs only in certain species.

The vast majority of these algae are autotrophs, and more rarely mixotrophs (autotrophic-heterotrophic); terrestrial species are capable of nitrogen fixation. In Ukraine, the most widespread blue-green algae include species from the genera *Nostoc*, *Anabaena*, *Lyngbya*, *Gloeocapsa*, *Oscillatoria*, and *Microcystis*.

Blue-green algae inhabit all environments, though predominantly aquatic habitats as components of plankton. There are also soil (edaphic) and aerial (aerophytic) species that colonize rocks, tree bark, the sands of the Sahara, and the ice of Antarctica. Among blue-green algae, thermophiles inhabit hot springs, while psychrophiles (cryophiles) thrive on ice, snow, and in cold streams. Some species enter into symbiotic relationships with fungi to form Lichens, or settle within the thalli of mosses or the leaves of certain ferns, acting as assimilators.

The ecological significance of blue-green algae is that during mass reproduction, they pollute water bodies, causing water "blooms," clog water intake facilities, and contaminate drinking water. However, at the same time, some of them are nitrogen fixers. Algae from the genus *Arthrospira*, known as "spirulina," have been brought into cultivation and are used in the food and medical industries. Soil species act as pioneer vegetation; by accumulating in significant quantities, they improve soil fertility.

Self-Assessment Questions

1. What is the cell structure of blue-green algae, and how does it differ from the structure of a bacterial cell?

2. What pigments are present in the cells of blue-green algae?

3. Where are blue-green algae distributed?

4. What reserve nutrients are stored in the cells of algae?

5. What structural elements comprise the centroplasm?

6. How do blue-green algae reproduce?

7. What is their role in nature?