Introduction

Kingdom Monera comprises unicellular and prokaryotic organisms, specifically bacteria. The term ‘Monera’ means ‘single’ or ‘solitary.’ H.F. Copeland first coined the term in 1866. R.H. Whittaker placed Monera as the first and most primitive kingdom in its highly acceptable five-kingdom classification. The organisms of this kingdom are prokaryotes, i.e., they lack a well-defined nuclear membrane. They also lack other double-membraned cell organelles like mitochondria, ER, chromatophores, dictyosomes, and vacuoles. Bacteria, the sole member of the kingdom Monera, are the most abundant microorganisms. If you take a handful of soil, you will get hundreds or even thousands of bacteria in it. The study of Salient features and classification of Monera comes under the zoology branch of science.

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Salient Features of Kingdom Monera

The salient features of Kingdom Monera that differentiate it from other kingdoms are as follows:

• Kingdom Monera only comprises prokaryotic, simplest, and primitive organisms
• Bacteria are the single member of this kingdom. However, there are different forms of bacteria
• They are usually present in moist environments
• They do not have a nuclear envelope. Only naked circular DNA is present as their genetic material
• They lack sap vacuoles. However, gas vacuoles are present in them
• Most of the Kingdom Monera members possess an absorptive mode of nutrition. However, some may be photosynthetic or chemosynthetic
• They may be motile or non-motile. The motile organisms have flagella for locomotion
• They possess 70s ribosomes

Bacteria- The Sole Member of Kingdom Monera

Bacteria are microscopic organisms that are present abundantly in the environment. They are present in different habitats like soil, water, acidic hot springs, wastes, and inside the earth’s crust. They are also present as symbiotic and parasitic relationships with plants. They are both harmful and beneficial for the environment. The bacteria reproduce mainly by fission (binary or multiple). However, the bacteria may reproduce by spores due to some unfavourable conditions. Animals and humans carry thousands to millions of bacteria in their gut and even on the skin. Thus, we can say bacteria are omnipresent. 

Shapes of Bacteria

Different bacteria vary in their shapes. These shapes are as follows:

• Cocci– These bacteria have an oval to spherical shape. There is micrococcus (single), diplococcus (pairs), trilococcus (three in number), Streptococcus (multiple in chains), and Staphylococcus (multiple in clusters) bacteria

An example of cocci bacteria is Streptococcus pneumonia. This bacterium is the causative agent of pneumonia in humans.  

• Bacilli– The bacilli bacteria are rod-shaped. They may or may not have flagella for locomotion

An example of bacilli bacteria is Bacillus cereus. 

• Vibrio– Vibrio-shaped bacteria resemble the ‘comma.’ They have a single flagellum at one end

An example of vibrio bacteria is Vibrio cholerae. The bacteria causes cholera disease in humans. 

• Spirillum– As the name suggests, the spirillum bacteria have a spiral body resembling the corkscrew. They have multiple flagella on one or both ends

An example of a spirillum bacteria is Campylobacter jejuni. 

Classification of Kingdom Monera

Kingdom Monera is subdivided into two other parts. These three sub-kingdoms are as follows:

• Archaebacteria– Archaebacteria is present in extremely harsh conditions or habitats. They are the oldest living organisms. They are often seen in extreme salty areas (halophiles), hot springs (thermoacidophiles), and marshy areas (methanogens). They have a distinct cell wall that enables their survival in such extreme conditions 

Examples of archaebacteria are Sulfolobus, Halococcus, Methanococcus, etc.

They have three distinct groups; Methanogens, Halophiles, and Thermoacidophiles. 

• Eubacteria– Eubacteria, often called true bacteria, have thousands of different bacteria in them. They can be unicellular to multicellular organisms. They can have different structures like spherical, oval, and rod-shaped. They have a rigid cell wall. They can be motile or non-motile. The motile eubacteria have flagella to grant motility

The photosynthetic eubacteria are called cyanobacteria (blue-green algae). They have chlorophyll, just like plants. Thus, they are autotrophs. These cyanobacteria are unicellular. They may be colonial or filamentous. The colonies of them are often surrounded by a gelatinous sheath. They may be present in freshwater, marine water, or even terrestrial habitats. 

Some of the eubacteria are capable of nitrogen fixation. These bacteria are called heterocysts (e.g., Nostoc). 

Besides, these autotrophic cyanobacteria, heterotrophic bacteria are abundant in the environment. They mostly act as decomposers. They are very helpful in our daily activities. These bacteria (lactobacillus) convert milk into curd. They are used in the pharmaceutical industry and in making several antibiotics. 

However, many bacteria cause severe damage too. They cause several diseases to humans as well as plants. Cholera, typhoid, and tetanus are common diseases by the specific bacterium in humans. In plants, they cause diseases like bacterial wilt, citrus canker, scab, etc. 

Conclusion 

The salient features and classification of Monera is an interesting topic that states the characteristics and classifications of bacteria. Monera contains primitive, prokaryotic organisms that lack a well-membrane nucleus and other well-developed organelles. There are two basic sub-division of this kingdom. They are Archaebacteria and Eubacteria. The bacterium has different shapes. It may be cocci, bacilli, vibrio, or spirillum. They are both harmful and beneficial for the environment.