Bacteria
These unicellular, prokaryotic organisms contain cell wall (feature of
plant cells only). These are approximately 4000 species of bacteria,
with cosmopolitan occurrence. Bacteria can be regarded both friends
and foes on the basis of interaction with human beings.
An average weight human (~ 70 kg) has about 2.5 kg of bacteria in the
form of gut microflora to supplement the proper digestion and other
metabolic functions
(i) Archaebacteria
These are the group of most primitive prokaryotes. They have a cell
wall, made up of protein and non-cellulosic polysaccharides. The
presence of 16 srRNA, makes them unique and helps in placing in a
separate domain called archaea between bacteria and eukarya.
Archaebacteria can live under extreme hostile conditions like salt
pans, salt marshes and hot sulphur springs. They are also known as
living fossils, because they represent the earliest form of life on earth.
Archaebacteria can be used for
(a) Experimentation for absorption of solar radiation.
(b) Production of gobar gas from dung and sewage.
(c) Fermentation of cellulose in ruminants.
(ii) Eubacteria
Eubacteria are ‘true bacteria’ which lack nucleus and membrane bound
organalles like mitochondria, chloroplasts, etc. Eubacteria are usually
divided into five phylums– Spirochetes, Chlamydias, Gram- positive
bacteria, Cyanobacteria and Proteobacteria.
Nutrition in Bacteria
The process of acquiring energy and nutrients., is called nutrition.
On the basis of mode of nutrition, bacteria are of two types–
autotrophic and heterotrophic. About 1% bacteria show autotrophic
mode of nutrition and the rest are of heterotrophic habit.
Chemosynthetic bacteria oxidise various inorganic substances such as
nitrates, nitrites and ammonia and use the released energy for their
ATP production.
Respiration in Bacteria Other Monerans
These are as follows
1. Mycoplasma
● It was discovered by Nocard and Roux i
1898. These are cell wall
less, aerobic and non-motile organisms. Due to the absence of cell wall
and pleomorphic nature, they are commonly called as jokers of living
world.
● The mycoplasmas are also known as Pleuro Pneumonia Like
Organisms (PPLO). These are the smallest living cells, yet
discovered, can survive without oxygen and are typically about 0.1 µm in diameter
2. Actinomycete
● The members of a heterogeneous group of Gram-positive, are
generally anaerobic bacteria noted for a filamentous and branching
growth pattern. It results in most forms in an extensive colony or
mycelium
● Morphologically, they resemble fungi because of their elongated cells
that branch into filaments or hyphae. During the process of
composting, mainly thermophilic and thermotolerent Actinomyces
are responsible for the decomposition of the organic matter at
elevated temperature.
● Generally, Actinomycetes grow on fresh substrates more slowly than
other bacteria and fungi. During the composting process, the
Actinomycetes degrade natural substances such as chitin or
cellulose.
● Natural habitats of thermophilic Actinomycetes are silos, corn mills
3. Cyanobacteria/Blue-Green Algae (BGA)
● They are Gram-negative photosynthetic prokaryotes which perform
oxygenic photosynthesis. These can live in both freshwater and
marine habitats and are responsible for ‘blooms’ in polluted water
(eutrophication).
● They have photosynthetic pigments, chlorophyll-a, carotenoids
and phycobilins and food is stored in the form of cyanophycean
starch, lipid globule and protein granules.
● Cyanobacteria have cell wall formed of peptidoglycan, naked DNA,
70S ribosomes and the absence of membrane bound organelles like
endoplasmic reticulum, mitochondria, Golgi bodies, etc.
● The red sea is named after the colouration provided by red coloured
cyanobacteria i.e., Trichodesmium erythraeum.
● Cyanobacteria can fix atmospheric nitrogen through a specific
structure called heterocyst. These are modified cells in which
photosystem-II is absent hence, non-cyclic photophosphorylation
does not take place. Nitrogen-fixation is performed through enzyme
nitrogenase, present in it.
4. Rickettsia
● These are small, aerobic and Gram-negative bacteria. They belong to
phylum–Proteobacteria, which are capable of growing in low level of
nutrients and have long generation time relative to other
Gram-negative bacteria.
● Rocky Mountain Spotted Fever (RMSF) is a tick borne human
disease caused by Rickettsia rickettsii, an obligate, intracellular
bacteria. , . s . n Respiration occurs in the plasma membrane of bacteria. Glucose is
broken down into carbon dioxide and water using oxygen in aerobic
cellular respiration and other molecules such as nitrate (NO ) 3
in
anaerobic cellular respiration.
Reproduction in Bacteria
Bacteria reproduce asexually and sexually both.
Asexual Methods
Asexually, bacteria reproduce by following methods
● Fission Bacteria divide both laterally and longitudinally.
● Budding Vegetative outgrowths result into new organisms after
maturity.
● Spore formation Non-motile spores like conidia, oidia and
endospores are formed.
Sexual Methods
Although sexes are not differentiated in bacteria, following methods of
genetic recombination are categorised under sexual reproduction in
bacteria.
● Transformation F Griffith (1928), Genetic material of one
bacteria is transferred to other through conjugation tube.
● Conjugation Lederberg and Tatum (1946), Transfer of genetic
material occurs through sex pili.
● Transduction Zinder and Lederberg (1952), Transfer of genetic
material occurs by bacteriophage.
Economic Importance of Bacteria
Economically, some bacteria are useful in producing various useful
substances like curd, cheese, antibiotics and vinegar, etc. While other
bacteria cause several chronic diseases in humans, plants and other animals etc .
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