The word Moneras is derived from Monos - means single hence moneras are unicellular, primitive organisms found without the nuclear membranes. The origin of Monera was first proposed by Ernest Haeckel in the year 1866, later on, in the year 1925, a complete taxonomical position was set by Edouard Chatton. According to Greek mythology, moneros means simple, it is the very basic forms of life. The characteristics of monera are as follows.
Table of Contents
2. Characteristics of Monera
3. Classification of kingdom Monera
3. 1 Archaebacteria
3. 3 Cyanobacteria
4 4 Spirillum
4.5 Filamentous bacteria
4.6 Stalked bacteria
4. 7 Budded bacterium
5. Structure of a typical bacteria
5.2 Cell wall
5.3 Plasma membrane
5.7 Pili or Fimbriae
Characteristics of Monera
They are single-celled organisms with no envelope around their genetic material.
They have only cell walls but not the cell membranes.
Monera contains very few necessary organelles such as ribosomes and simple chromatophore. Organelles like plastids, mitochondria, Golgi complex, lysosomes, endoplasmic reticulum and the centromeres are absent.
Monera forms gas vacuole instead of sap vacuoles .
Few monera organisms perform photosynthetic (holophytic) and chemosynthetic processes but their primary mode of nutrition is absorptive.
Moneras are characterized by the flagellar movement but they are not the actively motile organisms.
They measure about a few microns' in length.
Reproduction in Monera is primarily asexual; binary fission or budding.
The mitotic apparatus is not formed during cell division.
Classification of kingdom Monera
Kingdom Monera is divided into 3 sub-categories; Archaebacteria, Eubacteria, and Cyanobacteria.
1. Archaebacteria: Archaebacteria live in the extreme salty habitats, hot springs, and marshy areas. They are the most primitive organisms than any other bacterium. Their cell wall is very strong helping them to survive in any type of harsh environmental conditions. They are autotrophic in their nutrition as they can synthesize their own food. They have unique nucleotide sequences in their tRNA and rRNA are unique.
2. Eubacterium: Eubacterium is a highly variable group of species found in a variety of habitats. Eubacterium has a rigid cell wall made up of peptidoglycans. They are characterised by ciliary appendages called pili. Pili helping in their sexual reproduction as well as prey mechanism. By using the sticky projections-pili, they strongly stick against the hosts. Depending upon the nature of the cell wall and the stain they take, Eubacteria are divided into gram-positive and gram-negative. Some of the example are Rhizobium and Clostridium.
3. Cyanobacteria: Cyanobacteria are otherwise known as blue-green algae. They have chlorophyll hence they participate in photosynthesis. Eubacterium have carotenoids and phycobilins. They are found in the aquatic region. Some of Cyanobacteria help in fixing the atmospheric nitrogen. Most commonly found cyanobacterium are Nostoc, Anabaena, Spirulina.
Bacteria fall under Monera. Bacteria has a history of a solid 4 billion years on the earth. They were believed to be the first life forms on Earth. Bacterium vary in their structure, colonization, and ability to infect the hosts. They are classified based on the morphology, size, shape, structure, virulence and staining capacity. The most common classification is based on the shape as explained below.
1. Cocci exist in a spherical shape. They are further classified into micrococcus, diplococcus, pneumococcus, staphylococcus, and streptococcus. Being in the clusters, they can be seen under microscope.
2. Bacilli are rod-shaped with or without flagella. If they exist in single they are called simply bacillus but if they occur in pairs, they are called diplobacillus. Sometimes they occur in chain well known by the name streptococci.
3. Vibrios are comma(,) shaped and, very small in size. Under the ultramicroscope, they look like human`s kidney. Vibrios have a flagellum at one end helping in their motility. The most Well-known form of vibrio is Vibrio cholera.
4. Spirillum is a coil-shaped bacteria with 2 or more flagella, for example, Spirillum and spirochetes.
5. Filamentous bacteria is the one in which the body of the bacterium is filamentous for example; Beggiota and Thiothrix.
6. Stalked bacteria have a stalk for example; Caulobacter.
7. Budded bacterium is swollen for example; Rhodomicrobium
Structure of a typical bacteria
A typical bacteria with flagella
A typical bacteria have Capsule, cell wall, cell membrane, nucleus, Cytoplasm, ribosomes, plasmids, flagellum and nucleoid as shown in the diagram above. Let`s discuss each part in detail.
Capsule: It is the outermost thick coat made up of nitrogenous substances and amino acids. Bacteria with a strong coat are highly virulent in nature. For example, Bacillus, anthracite, Diplococcus pneumoniae and Mycobacterium tuberculosis.
Cell wall: It is a strong and rigid layer located between the cell membrane and the capsule. The cell wall is made up of proteins, polysaccharides, lipids, D-glutamic acid, and diaminopimelic acid.
Plasma membrane: It is located just beneath the cell wall. The plasma membrane is very thin and selectively permeable as it doesn't allow all the material through it.
Cytoplasm: It is an aqueous -fluid-filled compartment with a freely floating ground substance called matrix. Matrix provides nutritional support to the organelles by supplementing the necessary materials like water, proteins, vitamins, glucose, salts, enzymes and minerals. The organic matter found in the cytoplasm is colloidal in nature. It has a granular cytoplasm due to the presence of a large number of ribosomes. The membranous organelles such as mitochondria, endoplasmic reticulum, Golgi bodies, lysosomes, and vacuoles are absent in the bacterial cytoplasm. In some photosynthetic bacteria, the plasma membrane gives rise to large vesicular thylakoids rich in bacteriochlorophylls and proteins.
Nucleoid: It is also known as genophore, naked nucleus or incipient nucleus. Nucleoid encompasses nuclear material like DNA packed in the helical fashion
Plasmids: Plasmids are the extrachromosomal genetic elements in addition to the DNA. Plasmids are small, circular and double-stranded molecules.
Flagella: They are thin, stranded, fine, thread-like protoplasmic appendages. Flagellum extended through the cell wall and the slime layer of the flagellated bacterial cells help the bacteria to swim around within the liquid medium.
Pili or Fimbriae: Alongside flagella, some tiny or small hair-like outgrowths are present on the bacterial cell known as pili. Pili have a protein called pilin. A typical pili is about 0.5-2 mm in length and 3-5mm in diameter.
On the basis of mode of nutrition, bacteria are classified into autotrophic and heterotrophic bacteria. Autotrophic bacteria can synthesize food their own with the help of inorganic substances. The carbon required for their photosynthesis is derived from carbon dioxide. The hydrogen needed to reduce carbon to organic form comes from sources such as atmospheric H2, H2S or NH3. Heterotrophic bacteria doesn't synthesize their food so they prey on other organic materials, these are parasitic in nature as they can`t participate in photosynthesis.