Note on Bacteria

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The kingdom monera contains three major groups:

  • Bacteria
  • Cyanobacteria
  • Archaebacteria

Bacteria

Occurrence:

Bacteria are found everywhere in air, soil, water. They are most adaptative organisms which can grow in very cold climate like arctic region, hot spring, desert, on and inside organisms body.

Characters:

  • Bacteria are microscopic prokaryotic organisms.
  • The incipient nucleus is present which lacks nucleolus and nuclear membrane. Chromatin body forms long naked circular DNA without histone protein which is also called nucleoid.
  • Double membrane-bound cell organelles like mitochondria, endoplasmic reticulum, Golgi body, and plastids are absent.
  • 70's type of ribosome is present.
  • The cell wall is made up of muramic acid or peptidoglycan.
  • Reserve food material is found in the form of lipid and glycogen.
  • The gas vacuole is present.
  • Flagella is a primitive type which is single stranded.
  • Mode of nutrition is parasitic, saprophytic and autotrophic.
  • Reproduction mainly takes place by binary fission.
  • Sexual reproduction is almost absent if present it takes place by conjugation.
Forms or shape of bacteria
source:raise science.wordpress.com
fig:Forms or shape of bacteria

Types of bacteria:

On the basis of shape or morphology, bacteria are of following types:

Spherical bacteria( coccus or cocci):

Spherical bacteria are round-shaped bacteria. They lack flagella and are the smallest form of bacteria. It has different types they are:

Monococcus: They occur singlely.

Diplococcus: They are found in paired.

Tetracoccus: They are found in the group of four.

Streptococcus: They are found in a chain.

Staphylococcus: They are found in a cluster.

Rod- shaped bacteria(Bacillus):

They are short straight or slightly curved with a blunt end. Most of them contain flagella and few are without flagella. They are of following types:

Monobacillus: They are found in single.

Diplobacillus: They are found in a pair.

Streptobacillus: They are found in a chain.

Palisade: They occur parallelly.

Spiral bacteria (Helical):

Spiral bacteria are of following types:

Spirillum:

They are spirally twisted bacteria. They are larger in size than Bacillus and coccus. They contain flagella of one or both end.

Vibrio:

They are C-shaped or coma shaped bacteria. They contain single flagellum at one end.

Filamentous:

They are filamentous in shape. They have long thread-like(filamentous) structure.

Pleomorphic bacteria:

They can change their shape according to the environment. Eg; Azotobacter

Stalk bacteria:

They contain stalk. Eg: Caulobacter

Budding bacteria:

They have swollen structure at base end bud like outgrowth. Eg: Rhodomicrobacterium

Bacteria - Different kinds of flagellation in bacteria
source:notestrip11biology2.weebly.com
fig:Bacteria - Different kinds of flagellation in bacteria

Flagellation:

Flagella are small whips or hair like structures and acts as the organ of locomotion. Depending upon the presence and absence of flagella, the bacteria are of following types:

Atrichous: It is the type of bacteria without flagella.

Monotrichous: It is the bacteria having single flagellum at one end.

Amphitrichous: It contains single flagellum at both ends.

Cephalotrichous: It contains a group of flagella at one end.

Lophotrichous: It contains a group of flagella at both end.

Peritrichous: It contains a group of flagella found in all over the body surface of bacteria.

Gram positive and Gram negative Bacteria

Gram positive(+) Gram-negative(-)
They are those bacteria which retain the blue color of gram stain after they are washed with absolute alcohol. They are those bacteria which lose the blue color of gram stain after they are washed with absolute alcohol.
The cell wall is thick, but lipid composition is less. Cell wall is thin, but lipid composition is more.
The cell wall is single layered.

Cell wall is double layered.

They are less resistant towards antibiotics. They are more resistant towards antibiotics.
Few of them are pathogenic bacteria. Most of them are pathogenic bacteria.
Eg; Bacillus, Clostridium Eg; Escherichia, Salmonella.

  • Bacteria are found everywhere in air, soil, water. 
  • Bacteria are most adaptative organisms which can grow in very cold climate like arctic region, hot spring, desert, on and inside organisms body.
  • Bacteria are microscopic prokaryotic organisms.
  • Chromatin body forms long naked circular DNA without histone protein which is also called nucleoid.
  • Gram-positive bacteria are those bacteria which retain the blue color of gram stain after they are washed with absolute alcohol.
  • Gram-negative bacteria are those bacteria which lose the blue color of gram stain after they are washed with absolute alcohol.
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