Kingdom Monera

• @@Bacteria@@ are the sole members of the Kingdom Monera.
    * They are the %%most abundant microorganisms.%%
    * Bacteria occur almost everywhere.
• Hundreds of bacteria are present in a $handful of soil$$.$
    * They also occur in extreme habitats such as hot springs, deserts, snow, and deep oceans where very few other life forms can survive.
• Bacteria as a group show the %%most extensive metabolic diversity.%%
    * Bacteria are grouped under four categories based on their shape:
      * Coccus: spherical
      * Bacillus: rod-shaped
      * Vibrio: comma shaped
      * Spirillum: spiral.

Some of the bacteria are:

• Autotrophic, i.e., they synthesize their own food from inorganic substrates. They may be photosynthetic autotrophic or chemosynthetic autotrophic.
• Heterotrophic, i.e., they depend on other organisms or on dead organic matter for food.

Archaebacteria:

• They live in some of the harshest habitats such as extreme salty areas (halophiles), hot springs (thermoacidophiles), and marshy areas (methanogens).
• They differ from other bacteria in having a different cell wall structure which helps them to survive in extreme conditions.
    * Methanogens are present in the ^^gut of several ruminant animals^^ such as cows and buffaloes
• These are responsible for the ==production of methane== (biogas) from the dung of these animals.

Eubacteria:

• They are also referred to as %%‘true bacteria’.%%
    * They are characterized by the presence of a $rigid cell wall,$ $and if motile, a$ $flagellum$$.$

Photosynthetic Autotrophs:

The @@cyanobacteria@@ (also referred to as blue-green algae) have chlorophyll similar to green plants and are @@photosynthetic autotrophs.@@

• The cyanobacteria are %%unicellular, colonial, or filamentous, and freshwater/marine or terrestrial algae.%%
    * The colonies are generally surrounded by a @@gelatinous sheath@@@@.@@
    * They often form a bloom in %%polluted water bodies%%%%.%%
    * @@Some of these organisms can fix atmospheric nitrogen in specialized cells called heterocysts.@@
• Examples: $Anabaena and Nostoc.$

Chemosynthetic Autotrophs:

• These 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 sulfur.

Heterotrophic Bacteria:

• The majority of these are important decomposers.
• They are helpful in making curd from milk, production of antibiotics, fixing nitrogen in legumes, etc.

• Some are pathogens causing damage to human beings, crops, farm animals, and pets.
    * $Cholera, typhoid, tetanus, and citrus canker$ are well-known diseases caused by different bacteria.

Mycoplasm:

• These are organisms that completely %%lack a cell wall.%%
    * They are the ==smallest living cells== known and ==can survive without oxygen (anaerobic).==
    * Many mycoplasmas are $pathogenic$ in animals and plants.

Reproduction:

• Bacteria reproduce mainly by $fission.$
    * 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.^^