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Eubacteria, as an ancient and diverse microbial group on the earth, are widely distributed in every corner of our lives. From hot springs to cold polar regions, from fertile soil to deep oceans, there are traces of them. Although this kind of prokaryote is small, it occupies an irreplaceable key position in the operation of the ecosystem, and affects the material circulation and energy flow of the earth with its unique cell structure and metabolic mode.
This paper introduces the main characteristics of eubacteria, and their relationship with ecosystem and human beings, it also fully shows the important position and role of eubacteria in nature and human life.
What is Eubacteria
Eubacteria, as a key member of prokaryotic domain, occupies an important position in the microscopic world. They have a unique cell structure, and the cell wall is composed of peptidoglycan, which provides protection and shape support for cells. Its metabolic types are extremely diverse, from photoautotrophic cyanobacteria, which convert carbon dioxide into organic matter by sunlight, to chemoheterotrophic Escherichia coli, which obtains energy and carbon sources by decomposing organic matter in the environment, covering almost all possible survival strategies and showing strong adaptability.
Eubacteria are widely distributed in soil, water and organisms. Bacteria in soil help material circulation and nutrient transformation; Bacteria in water participate in key ecological processes such as nitrogen cycle; In organisms, such as Bifidobacterium in human intestine, they maintain microecological balance and promote digestion and nutrient synthesis. However, some eubacteria are pathogenic bacteria, such as Streptococcus pneumoniae, which can cause pneumonia and pose a threat to health. The relationship between eubacteria and human beings can be described as mixed advantages and disadvantages.
Basic Characteristics of Eubacteria
Eubacteria belong to prokaryote, the cell nucleus is wrapped by nuclear membrane, and DNA is concentrated in pseudonucleus. The cell wall contains peptidoglycan. Rich in shape, there are spherical, rod-shaped, spiral and so on. The size is usually small, mostly between 0.5 and 5 microns. Although small, it occupies a diverse and key position in the ecosystem because of its diverse structure and morphology.
Cellular Structure
Cell wall: the main component is peptidoglycan, which is a unique component of the cell wall of eubacteria. Peptidoglycan is composed of polysaccharide chain skeleton, tetrapeptide side chain and pentapeptide cross-linked bridge, which has a tough structure and can protect cells from the influence of external osmotic pressure and maintain cell morphology. The cell wall structure and composition of different kinds of eubacteria are slightly different. For example, the cell wall of Gram-positive bacteria is thick, with many peptidoglycan layers and containing phosphomuramic acid. Gram-negative bacteria have thin cell walls and few peptidoglycan layers, and the outer membrane contains lipopolysaccharide and other components.
Cell membrane: It is a biomembrane composed of phospholipid bilayer and protein. The hydrophilic head of phospholipid molecules faces the inner and outer sides of the membrane, and the hydrophobic tail is located in the middle of the membrane. Cell membrane has selective permeability, which can control substances entering and leaving cells, and also participate in important physiological processes such as signal transduction and energy conversion of cells.
Cytoplasm: it is a gelatinous substance in cells, including ribosomes, plasmids, storage particles and other structures. Ribosome is the site of protein synthesis. The ribosome of eubacteria is 70S, which consists of 50S and 30S subunits. Plasmid is a small circular double-stranded DNA molecule, which can carry some special genes, such as resistance genes, and can be transferred between cells, giving bacteria new characteristics. Storage particles are used to store nutrients, such as glycogen, poly-β-hydroxybutyric acid, etc., so as to be used by cells when nutrition is deficient.
Eukaryote: Eubacteria have a nucleus without a nuclear membrane, and its genetic material DNA is concentrated in a region of the cell, which is called eukaryote. The DNA in the pseudonucleus is usually a circular double-stranded molecule, which carries the main genetic information of bacteria and controls the basic life activities of bacteria such as growth, reproduction and metabolism.
Eubacteria cellular structure diagram
Eubacteria Morphology
Sphere: Cells are spherical or nearly spherical, which can be divided into monococcus, diplococcus, streptococcus, staphylococcus and so on according to the different arrangement of cells. For example, pneumococcus is diplococcus, and Staphylococcus aureus is Staphylococcus.
Rod-shaped: Cells are rod-shaped, which is a common form in eubacteria. The length and thickness of rod-shaped bacteria vary with species, and some bacilli have short oval cells, which are called Brevibacterium. Some bacilli have longer cells, such as Bacillus subtilis. There are also many ways to arrange bacilli, such as single bacilli and streptococci.
Spiral: Cells are spiral, which can be divided into Vibrio and Spirillum according to the degree and shape of spiral. The thallus of Vibrio has only one bend, which is arc-shaped or comma-shaped, such as Vibrio cholerae; The thallus of Spirillum has many bends and is spiral, and the number of spiral turns and pitch of Spirillum vary from species to species.
Size Range
The size of eubacteria varies greatly, but generally speaking, its cell diameter is usually between 0.5 and 5 μ m. The diameter of cocci is mostly 0.5-2 μm, for example, the diameter of Staphylococcus aureus is about 0.8-1 μm. The size of Bacillus is usually expressed by width × length, and the width is generally 0.5-1 μm and the length is about 1-5 μm, for example, the size of Escherichia coli is about 0.5-0.8 μm× 1-3 μm. Spirillum is more diverse in size, with a width of 0.2-2 μm and a length of 2-20 μm.
Where Does Eubacteria Live
The living environment of eubacteria is extremely extensive, covering almost every corner of the earth. Soil is an important habitat for eubacteria. Soil is rich in organic matter, such as animal and plant residues and humus, which provides sufficient carbon and nitrogen sources for eubacteria. Different types of soil are pregnant with diverse eubacteria communities due to differences in pH, texture, aeration and nutrient content. For example, acidophilic bacteria are abundant in acidic soil, while nitrogen-fixing bacteria and nitrifying bacteria are abundant in nitrogen-rich soil.
Water is also a place where true bacteria live in large numbers, whether it is fresh water rivers, lakes or vast oceans. As decomposers, eubacteria in water can decompose organic pollutants into inorganic substances and maintain the ecological balance of water. Some photosynthetic bacteria carry out photosynthesis to provide oxygen and organic matter for themselves and other aquatic organisms, which is the basic link of water food chain.
Eubacteria also exist widely in organisms and form symbiotic or parasitic relationships with organisms. There are a large number of beneficial bacteria in human and animal intestines, such as Bifidobacterium and Lactobacillus, which can help digest food, synthesize vitamins and maintain intestinal mucosal barrier function. In terms of plants, rhizobia coexist with leguminous plants, rhizobia fix nitrogen for plants, and plants provide them with living environment and nutrition. However, there are also pathogenic bacteria such as Streptococcus pneumoniae and Mycobacterium tuberculosis that parasitize organisms and cause diseases.
Eubacteria can also survive in some extreme environments. For example, thermophilic bacteria can survive in high-temperature hot springs, deep-sea hydrothermal vents and other environments, and their cell structure and metabolic mechanism adapt to high-temperature conditions; Halophilic bacteria can multiply in high salinity salt lakes, saltworks and other environments, and they cope with high salinity environment through special osmotic pressure regulation mechanism.
Taxonomy of the B. braunii bacterial community and selected functional categories encoded in reconstructed MAGs and complete genomes (Blifernez-Klassen et al., 2021)
Relationship Between Eubacteria and Ecosystem
Eubacteria play a key role in the ecosystem. As decomposers, they can decompose complex organic substances such as animal and plant residues into simple inorganic substances and promote material circulation; Some photosynthetic eubacteria can carry out photosynthesis and provide oxygen and energy for the ecosystem; Some of them are symbiotic with organisms, helping to transform nutrients, etc., which is of great significance to maintaining ecological balance.
Carbon Cycle
Decomposition of organic matter: A large number of heterotrophic eubacteria act as decomposers in the ecosystem. They can gradually decompose complex organic carbon compounds such as animal and plant residues and humus. For example, Bacillus, Clostridium in soil, etc., by secreting extracellular enzymes, degrade macromolecules such as polysaccharides, protein and fats into micromolecules such as sugars, amino acids and fatty acids, and then further oxidize and decompose them into carbon dioxide. This process promotes the transformation from organic carbon to inorganic carbon, which makes carbon return to the atmosphere and participate in a new round of carbon cycle.
Participate in photosynthesis (some bacteria): Photoautotrophic eubacteria such as cyanobacteria contain photosynthetic pigments such as chlorophyll, which can be used for photosynthesis. They use light energy to convert carbon dioxide and water into organic matter and release oxygen at the same time. Cyanobacteria are widely distributed in marine and freshwater ecosystems, and the amount of carbon fixed by photosynthesis is considerable every year, which plays an important role in the global carbon cycle, not only providing material basis for their own growth, but also providing organic carbon sources and oxygen for other organisms.
Physiological effect of the individual bacterial isolates on the microalgae during co-cultivation (Blifernez-Klassen et al., 2021)
Nitrogen Cycle
Nitrogen fixation: Nitrogen-fixing bacteria such as rhizobia and leguminous plants form a symbiotic relationship. Rhizobium invades plant root cells, which promotes the formation of root nodules. In the nodule, rhizobia use nitrogenase carried by themselves to convert the free nitrogen in the air into ammonia, and then synthesize organic nitrogen compounds such as amino acids for plants to use. In addition, there are some autotrophic nitrogen-fixing bacteria, such as azotobacter chroococcum, which can independently fix nitrogen in the soil, increase the nitrogen content in the soil and provide a key nitrogen source for plant growth, which is of great significance for maintaining the nitrogen balance of the ecosystem.
Nitrification: Nitrifying bacteria include nitrite bacteria and nitrate bacteria. Nitrite bacteria oxidize ammonia into nitrite, and nitrate bacteria further oxidize nitrite into nitric acid. This process transforms ammonia nitrogen in soil into nitrate nitrogen, which is more easily absorbed and utilized by plants. Nitrification plays a key role in soil nitrogen transformation, affecting plant growth and ecosystem productivity.
Essential cofactors (inter-)dependencies of the bacterial core community and isolates of B. braunii (Blifernez-Klassen et al., 2021)
Importance of Eubacteria to Ecological Balance
Adjusting the number of biological populations: Eubacteria can adjust the number of biological populations through symbiosis and competition with other organisms. Symbiosis promotes the interdependence and co-evolution among organisms, while competition restricts the excessive growth of some biological populations. For example, the symbiosis between rhizobia and leguminous plants promotes the growth and reproduction of leguminous plants, and in the same niche, the competition between bacteria controls the size of their respective populations, maintaining the relative stability of biodiversity and population structure in the ecosystem.
Stabilizing ecosystem functions: Eubacteria participate in various ecological processes, such as soil fertility maintenance and water self-purification, which are very important for stabilizing ecosystem functions. In sewage treatment, the organic pollutants in sewage are decomposed by bacteria, so that the water body is purified and the health of aquatic ecosystem is maintained. In soil, eubacteria participate in substance transformation and nutrient circulation, which maintains soil fertility, provides a suitable environment for plant growth, and then supports the stability of the whole terrestrial ecosystem.
In carbon cycling, fungal genome sequencing (e.g., lignin-degrading enzymes in white-rot fungi) complements eubacterial cellulose degradation. Metagenomic sequencing reveals synergistic networks between fungi and eubacteria in soil ecosystems. During nitrogen fixation, transcriptomic studies of arbuscular mycorrhizal fungi (e.g., Glomus spp.) highlight cross-kingdom gene regulation with nitrogen-fixing bacteria.
The Connection of Eubacteria to Human Beings
The relationship between eubacteria and human beings is complicated, which not only makes many positive contributions to human life, but also brings negative effects in some aspects. The relationship between eubacteria and human beings is elaborated in detail from two angles: beneficial and harmful.
Beneficial Aspect
Application in food industry: Eubacteria play an indispensable role in the field of food fermentation. Lactic acid bacteria is a typical representative, which can ferment sugar to produce lactic acid and is widely used in the production of yogurt, pickles, sauerkraut and other foods. In the production of yogurt, lactic acid bacteria convert lactose in milk into lactic acid, which reduces the pH value of milk, promotes protein coagulation and endows yogurt with unique sour taste and texture. In addition, Acetobacter can oxidize alcohol into acetic acid, which can be used for vinegar brewing and add unique flavor to vinegar.
Medical and health contribution: Many eubacteria provide key resources for the development of modern medicine. On the one hand, through genetic engineering technology, the gene of protein needed by human beings is introduced into bacterial cells, and drugs are produced in large quantities by taking advantage of the rapid reproduction of bacteria. On the other hand, the secondary metabolites produced by some bacteria have antibacterial and antiviral medicinal values.
Environmental purification: Eubacteria play an important role in the material circulation and environmental purification of the ecosystem. In the sewage treatment plant, aerobic bacteria and anaerobic bacteria work together to decompose organic pollutants in sewage. Aerobic bacteria use oxygen to completely oxidize and decompose organic matter into carbon dioxide and water, while anaerobic bacteria convert complex organic matter into methane and other gases under anaerobic conditions. Metatranscriptomics tracks fungal-bacterial consortia in bioremediation (e.g., Aspergillus-Pseudomonas synergy in oil degradation), combining long-read sequencing for pathway reconstruction.
The roles of gut microbiota and short-chain fatty acids (Wu et al., 2023)
Harmful Aspect
Cause human diseases: Some eubacteria are pathogenic and seriously threaten human health. Streptococcus pneumoniae is one of the main pathogens causing pneumonia. It can spread through airborne droplets and infect human lungs, resulting in fever, cough, dyspnea and other symptoms. Tuberculosis caused by Mycobacterium tuberculosis is a chronic infectious disease, which spreads through the respiratory tract and causes a large number of patients’ deaths worldwide.
Food spoilage: Many eubacteria can cause food spoilage and economic losses. Pseudomonas bacteria can still grow and reproduce in low temperature environment, which often leads to the deterioration of frozen food, making food appear odor, discoloration, texture change and other phenomena. Botulinum botulinum will produce botulinum toxin when it grows in anaerobic environment, which is a highly toxic neurotoxin. Even a very small amount can cause serious food poisoning and threaten the safety of consumers.
Affect industrial materials: In the industrial field, eubacteria may also bring harm. Sulfate reducing bacteria (SRB) is a common corrosive bacteria, which can grow on metal surface, produce acidic substances such as hydrogen sulfide through metabolic activities, accelerate metal corrosion, cause serious damage to metal structures such as oil pipelines, ships and bridges, increase maintenance costs, and even affect the safe operation of industrial facilities.
Bacteriophages contribute to the genetic and physiological traits of their hosts thereb influencing host-microbe interactions (Chatterjee et al., 2018)
Conclusion
Eubacteria, as prokaryotes, contain unique peptidoglycan in the nucleus and cell wall wrapped by nuclear-free membrane. Its metabolic types are diverse, including light energy, chemical energy autotrophic and heterotrophic. Breeding is mainly based on efficient binary fission, and spores can be formed when it is bad. In ecology, soil, water and organisms are all distributed, which is of great significance to the material cycle and energy conversion of the ecosystem, closely related to human production and life, and is an indispensable part of the earth’s ecology.
Learn More:
- Introduction to Eubacteria: Taxonomy, Reproduction, Metabolism and Research Methods
- Unraveling Fungi through Sequencing: Approaches and Applications
References
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