Kingdom Monera

Bacteria are the sole members of the Kingdom Monera. They are the most abundant micro-organisms. Bacteria also live in extreme habitats such as hot springs, deserts, snow and deep oceans where very few other life forms can survive. Many of them live in or on other organisms as parasites.

Bacteria are grouped under four categories based on their shape:

· The spherical Coccus (pl.: cocci)

· The rod-shaped Bacillus (pl.: bacilli)

· The comma-shaped Vibrium (pl.: vibrio)

· The spiral Spirillum (pl.: spirilla)

Bacteria of different shapes

All prokaryotic organisms were grouped together under Kingdom Monera. Bacteria cell wall is made up of peptidoglycan.

Some of the bacteria are autotrophic, i.e., they synthesize their own food from inorganic substrates. They may be photosynthetic autotrophic or chemosynthetic autotrophic. The vast majority of bacteria are heterotrophs, i.e., they do not synthesize their own food but depend on other organisms or on dead organic matter for food.

Archaebacteria:

· These bacteria are special since they live in some of the most harsh habitats such as extreme salty areas (halophiles), hot springs (thermoacidophiles) and marshy areas (methanogens).

· Archaebacteria differ from other bacteria in having a different cell wall structure and this feature is responsible for their survival in extreme conditions. 

· Methanogens are present in the guts of several ruminant animals such as cows and buffaloes and they are responsible for the production of methane (biogas) from the dung of these animals.

Methane from Cow

· Archaea cell wall does not contain peptidoglycan.

Eubacteria:

· There are thousands of different eubacteria or ‘true bacteria’. They are characterized by the presence of a rigid cell wall, and if motile, a flagellum. The cyanobacteria (also referred to as blue-green algae) have chlorophyll a similar to green plants and are photosynthetic autotrophs.

· The cyanobacteria are unicellular, colonial or filamentous, freshwater/marine or terrestrial algae. The colonies are generally surrounded by gelatinous sheath.

· They often form blooms in polluted water bodies.

Algal bloom

· Some of these organisms can fix atmospheric nitrogen in specialized cells called heterocysts, e.g., Nostoc and Anabaena.

A filamentous blue-green algae – Nostoc

· Chemosynthetic autotrophic bacteria oxidize various inorganic substances such as nitrates, nitrites and ammonia and use the released energy for their ATP production. They play a great role in recycling nutrients like nitrogen, phosphorous, iron and Sulphur.

· Heterotrophic bacteria are the most abundant in nature. The majority are important decomposers.

· They are helpful in making curd from milk, production of antibiotics, fixing nitrogen in legume roots, etc. Some are pathogens causing damage to human beings, crops, farm animals and pets. Cholera, typhoid, tetanus, citrus canker are well known diseases caused by different bacteria.

· Bacteria reproduce mainly by fission.

A dividing bacterium

Sometimes, under unfavorable conditions, they produce spores. They also reproduce by a sort of sexual reproduction by adopting a primitive type of DNA transfer from one bacterium to the other.

The Mycoplasmas are organisms that completely lack a cell wall. They are the smallest living cells known and can survive without oxygen. Many mycoplasma are pathogenic in animals and plants.

Mycoplasma Tuberculosis

Mycoplasma conjunctivitis

Mycoplasma Pneumonia

Mycoplasma Rash