The Kingdom Monera consists of prokaryotes that are unicellular microorganisms that are most abundantly found in the world.
Monera is made up of prokaryotic bacteria that are single-celled microorganisms. Monera has been classified under various classification systems: the three-kingdom system (by Haeckel 1866), the four-kingdom system (by Copeland 1956), the five-kingdom system (by Whittaker 1969), and the six-kingdom system (by Woese 1977). Monera has three subkingdoms: archaebacteria, eubacteria, and cyanobacteria. Archaebacteria can survive in harsh environments; eubacteria can be beneficial or harmful to other living organisms; and cyanobacteria are found in aquatic environments. Bacteria have a simple cell structure that lacks membrane-bound cell organelles and lacks a definite nucleus compared to eukaryotes. Therefore, they are prokaryotic organisms. There are some bacteria, like mycoplasma, that do not have a cell wall. However, most bacteria in this kingdom have a capsule that encloses the cell to protect the bacteria from damaging the cell.
Monerans are bacteria belonging to the Kingdom Monera that can survive in diverse conditions. They are abundantly found in various parts of the world. Monerans were the first single-celled microorganisms to evolve around 3.5 billion years ago. Most bacteria are unicellular, but some cyanobacteria species are filamentous and multicellular. They do not contain a definite nucleus and consist of only a few cell organelles.
The size of monerans ranges from 0.1 to 10 micrometers. The genetic material of the bacteria is a circular chromosome having DNA genes encoded for the bacterial traits. They replicate through binary fission, where the cell is divided rapidly and adapts to different conditions through genetic mutations. This is achieved by various methods like transduction, conjugation, and transformation. Since they can adapt to other conditions, they are found everywhere in the atmosphere and on the surface. Hence, they are a significant source of contaminated food. However, some beneficial bacteria can be utilized in the food, cosmetics, and pharmaceutical industries.
Monerans can be both harmful and beneficial. A few of the disease-causing bacteria are Salmonella typhi (cause of typhoid), Mycobacterium tuberculosis (cause of tuberculosis), Vibrio cholerae (cause of cholera), Clostridium tetani (cause of tetanus), and Corynebacterium diphtheria (cause of diphtheria). Lactobacillus (ferments lactose to lactic acid), Azotobacter (fertile soil and fixes atmospheric nitrogen), Rhizobium (fix atmospheric nitrogen and are found in plant roots), Streptomyces (antibiotic streptomycin), and methanogens (in sewage treatment) are examples of beneficial bacteria.
Characteristics of Monera
Monerans have four types of nutritional modes: autotrophic (ability to produce their own food), saprotrophic (feed on dead organic matter), symbionts (utilize food from the host and provide benefits to the host), and parasitic (gain nutrition from a host and cause harm). The respiratory methods of the bacteria are either aerobic (they require oxygen for growth) or anaerobic (they do not require oxygen). The primary form of reproduction is binary fission through asexual means. In binary fission, the cell is divided into two after the DNA is replicated. Some bacterial species can reproduce sexually by two bacteria coming close together and exchanging genes. The bacteria then separate to replicate and divide into two cells.
Unicellular bacteria consist of a rigid cell wall composed of peptidoglycan, polysaccharides, lipids, and some proteins. However, they do not contain membrane-bound organelles and have ribosomes that are in their 70s. The plasma membrane, the next layer to the cell wall, is composed of lipids and proteins enveloping the cytoplasm and other cell compounds. The genetic material is a chromosome containing DNA in the nucleoid. Some bacterial species have more than one DNA ring called plasmids, containing antibiotic resistance genes, acting as a sex factor, and replicating along with their chromosomes. Pili are short hair-like structures found at the outer surface of the bacterial cell that are responsible for attaching themselves to a host. The bacteria contain flagella that help in their locomotion towards nutrition and away from predators.
The bacteria are further divided based on their shape: Cocci (spherical or oval-shaped), Bacilli (rod-shaped and flagellated or non-flagellated), Vibrios (comma-shaped having flagella), Spirillum (spiral-shaped or like a corkscrew having more than two flagella on each end), Filament (the bacterial body is filamentous), Stalked (the bacterial body has a stalk), and Budded (some areas of the bacteria are swollen).
The Classification of Monera
The Kingdom Monera has been classified into Archaebacteria, Eubacteria, and Cyanobacteria.
This group of microorganisms has been considered ancient as they evolved separately from the cyanobacteria and eubacteria. Archaebacteria are capable of surviving in extreme and harsh conditions. Hyperthermophilic archaebacteria can survive under higher temperatures ranging from 80-110°C and are unable to thrive below 60°C. This type of archaebacteria is found in submarine hydrothermal areas, volcanic vents, hot springs, etc., such as Pyrodictium. Furthermore, archaebacteria can thrive in freezing temperatures, and the largest population of archaebacteria is found in cold environments, such as deep in the arctic glaciers. Archaebacteria can additionally survive in high-pressure environments, hypersaline environments (halophiles), acidic ph conditions, and methanogens that produce methane. Their ability to survive in such extreme conditions is due to their cell wall structure. They are autotrophic (make their food) and have unique tRNA and rRNA sequences.
Eubacteria consists of two types based on their ability to retain dye stain: gram-positive and gram-negative. This group of bacteria is also known as “true bacteria” and is found abundantly in nature
and other organisms. Eubacteria can be divided based on their reaction to gram-stain: gram-positive and gram-negative. The cell wall of eubacteria is composed of peptidoglycans, which are rigid to maintain the shape of the bacteria. This group of bacteria contains flagella that assist them with their locomotion to move towards nutrition and away from predators. Some eubacteria have pili, a small hair-like structure around the cell surface, which plays a role in sexual reproduction and attaching itself to a host; for example, rhizobium, lactobacillus, etc.
Cyanobacteria are known as blue-green algae as they are aquatic bacteria. They are photosynthetic, and with the help of chlorophyll, phycobilins, and carotenoids, they can produce their food. Some cyanobacteria species can fix atmospheric nitrogen. One of the contributions to the evolution of cyanobacteria is the origin of plants. The chloroplasts that prepare their food are the cyanobacterium inside the plants. A few examples of cyanobacteria are spirulina, nostoc, etc.