The Kingdom Monera includes organisms that are single-celled known as bacteria. The microorganisms in Kingdom Monera are considered as the most ancient living forms on earth. The kingdom is divided into two groups Archaebacteria and Eubacteria. All the organisms of this kingdom are prokaryotes. These cells do not have nuclear membrane, the chromosome is a single and circular, they also lack membrane bound cellular organelles. This kingdom includes bacteria, cyanobacteria, mycoplasma etc. They are unicellular organisms and do not have specific mode of nutrition. They can be either aerobic or anaerobic.These organisms have cell wall which is made up of peptidoglycans. The cell organelles are not membrane bound. Cell organelles like endoplasmic reticulum, mitochondria are absent. Reproduction is by spore formation and binary fission.
General characteristics of the kingdom Monera are as follows:
- They are primitive organisms.
- All organisms of the kingdom are prokaryotes.
- They are present in both living and non-living environment.
- They can survive in harsh and extreme climatic conditions like in hot springs, acidic soils etc.
- They are unicellular organisms.
- Membrane bound nucleus is absent.
- DNA is in double stranded form, suspended in the cytoplasm of the organism,referred as nucleoid.
- A rigid cell wall is present.
- Membrane bound cellular organelles like mitochondria are absent.
- Habitat - Monerans are found everywhere in hot springs, under ice, in deep ocean floor, in deserts and on or inside the body of plants and animals.
- Nutrition - autotrophs - can prepare their own food, heterotrophs - depend on others for food, saprophytes - feed on dead and decaying matter, parasitic - live on other host cells for survival and cause, symbiotic - in mutual relation with other organisms, commensalism - it is where one organism is benefited and the other is not affected, mutualism - where both the organisms are benefited.
- Respiration - respiration in these organisms vary, they may be obligate aerobes - the organisms must have organisms for survival; obligate anaerobes - the organisms cannot survive in the presence of oxygen; facultative anaerobes - these organisms can survive with or without oxygen.
- Circulation - is through diffusion.
- Movement - is with the help of flagella.
- Reproduction is mostly asexual, sexual reproduction is also seen. Asexual reproduction is by binary fission, sexual reproduction is by conjugation, transformation and transduction.
Kingdom Monera has been classified into two groups - Archaebacteria and Eubacteria.
Archaebacteria are microbes that live in extreme and harsh conditions, they are known as extremophiles. These bacteria lack cell wall, their cell membrane is made up of different lipids, and their ribosomes are similar to that of eukaryotes.
Archaebacteria are of three major groups of bacteria based on their habitat i.e., thermophiles, halophiles and methanogens.
Some extremophiles live in boiling water like geysers of Yellowstone National Park and and in volcanoes. These are known as 'thermophiles'.
Some extremophiles live in extremely salty water, the salt loving bacteria are known as 'halophiles'.
Some bacteria are present in the guts of ruminants and are responsible for production of methane gas from their dung. These bacteria are known as 'methanogens'.
Eubacteria are true bacteria. The characteristic feature is the presence of rigid cell wall and if present a motile flagelllum that aids in locomotion.These organisms are characterized based on their nutrition and their shapes.
Classification based on Shape
Bacteria can be classified in four groups based on shape : Spherical or round shaped bacteria are called cocci, Rod-shaped are bacilli, Comma-shaped bacteria are vibrio and spiral shaped bacteria are spirilla.
Classification Based on Mode of Nutrition
Based on the mode of nutrition bacteria are broadly classified into Autotrophic and Heterotrophic.
Autotrophic bacteria - Bacteria which prepare their own food are autotrophic. (Example Cyanobacteria)
Heterotrophic bacteria - Bacteria which are dependent on other organisms for their food are heterotrophic.(Example Escherichia coli)
Autotrophic bacteria can be Chemosynthetic or Photosynthetic.
Chemosynthetic bateria are those which prepare their food with the help of inorganic substrates. Photosynthetic bacteria are autotrophic bacteria which prepare their own food by the process of photosynthesis.
Cyanobacteria (Blue-green algae) - They have chlorophyll similar to plants and hence they are photosynthetic autotrophs. The marine and terrestrial and they may be unicellular, colonial or filamentous. The colonies are surrounded by gelatinous sheath. They can also fix atmospheric nitrogen.
Example: Nostoc and Anaebena.
Chemosynthetic autotrophs - these organisms oxidise substances like nitrites, nitrates, ammonia etc. The help in recycling substances like nitrogen, sulphur, iron etc.
Heterotrophic bacteria are those which are dependent on other organism either directly or indirectly for their nutrition. They are most abundant and are important decomposers. Some are helpful in curdling milk, production of antibiotics, in nitrogen fixation and some are pathogens.
Heterotrophic bacteria can be parasitic and saprophytic. Parasitic bacteria are those which depend on the host for nutrition and cause harm to the host. Saprophytic bacteria feed on dead and decaying matter.
Symbiotic - it is a type where the bacteria are in mutual relation with other organisms. Symbiosis is of two types mutualism and commensalism. Mutualism is where the bacteria and the other organism are benefited due to the relationship. Commensalism is a relationship where the bacteria is benefited while the other organism is not affected by the relationship.
Classification based on Gram's staining
Gram's staining is a test on cell walls developed by Hans Christian Gram. This method helps classifying bacteria into Gram positive bacteria and Gram negative bacteria.
Gram Positive Bacteria - The bacteria's cell wall is made up of protein-sugar complex that takes on purple color during gram staining.
Gram Negative Bacteria - The gram negative bacteria has an extra layer of lipid on the outside of the cell wall and appear pink during the Gram staining procedure.
Reproduction in Bacteria
Reproduction in bacteria is mainly by fission.Under unfavourable conditions they reproduce by spores. Sexually bacteria reproduce by a primitive mode of DNA transfer from one bacterium to another i.e., by conjugation, transduction or transformation. Mycoplasma
Mycoplasma are the known to be the smallest living cells. They completely lack cell wall and can survive without oxygen. Most of the mycoplasma are pathogenic in nature in animals and plants.
Economic Importance of Bacteria
Lactic acid bacteria like Lactobacillus
have been used in fermentation
process for thousands of years.
The ability of the bacteria to degrade variety of organic compounds has been used in waste management processing and biorememdiation.
In pest control
, bacteria can be used in the place of pesticides as these pesticides are regarded environmentally friendly.
Example: Bacillus thuringenesis.
The ability of the bacteria in dividing rapidly and by studies on the bacterial genome, these bacteria can be bio-engineered for the production of therapeutic proteins
like insulin, growth factors and antibodies, etc.
The Monerans comprises of mostly bacteria. Following are a few well known examples.Blue-green algae
, Cocci shaped bacteria
, Bacilli shaped bacteria
, Vibrio shaped
- Vibrio cholerae
(cholera), Spiral shaped bacteria - Treponema pallidum
(syphilis). Gram positive bacteria
- Mycobacterium; Gram negative bacteria
(coliforms)Escherichia coli, Pseudomonas aeruginosa, Proteus vulgaris, Streptococcus pyogens, Clostridium botulinum, Listeria monocytogenes, Salmonella enterica, Vibrio cholerae, Bacillus anthracis, Bacillus cereus.