Bacteria can form specialized, morphologically differentiated structures. Describe them.
Bacteria can form specialized, morphologically differentiated structure: 1) forms that serve to reproduce 2) resting forms 3) cells with specialized metabolic functions
Reproduction forms
B
aeocytes
– formed by repeated multiple divisions of the mother cell
(Cyanobacteria)
For
example, It
starts out as a small, spherical cell. This cell is referred
to as a baeocyte (which
literally means ·small
cell·). The
baeocyte begins to grow, the cellular DNA is replicated over and
over, and the cell produces a thick extracellular matrix. The
vegetative cell eventually transitions into a reproductive phase
where it undergoes a rapid succession of cytoplasmic fissions to
produce dozens
or
even hundreds
of
baeocytes. The extracellular matrix eventually tears open,
releasing the baeocytes.
2) Hormogonium – adaptation in filamentous forms of Cyanobacteria for reproduction by fragmentation of filaments. Each Hormogonium can give rise to a new individual. If a group of cells, similar to Hormogonium, wearing thick coat, it is called gormospores (gormocysts), which also serves the function and reproduction, and the shifting of adverse conditions.
3) Gonidium – broad cell of Algae; each of which give rise to new growth, are produced within the mother cell, or are formed from the top of the mother cell. Gonidium is an obsolete form of conidium, also called Cocci or Planococci. Gonidium retain mucosa. Cocci lack clearly defined coats. Planococci too naked, but are capable of active movement.
4) Exospores (Actinomycetes)
single Exospores (Micromonospora)
Chains of spores on the end of hypha of aerial mycelium (Streptomyces)
Formed inside the sporangium (Streptosporangium)
Resting forms
Dormant form of bacteria
Cysts. Have two coats: Intine and Exine. Contain poly-beta-hydroxybutyric acid (Azotobacter). Cysts form some methanotrophic and oligotrophic bacteria, Spirochetes, Rickettsia
Microcysts(Mixocysts) Resting forms in Myxobacteria (Myxococcus, Chondromyces, Stigmatella). Have a thick coat. Aggregate, forming fruiting bodies. Fruiting bodies are a mass of mucus, which shipped cysts. Raised above the surface of the substrate by simple or branched stems. Fruiting body contains 10000-1000000 mixospores .
Akinetes -a form of resting spore. Large, thick-walled , resistant cells. Akinetes containing a food reserve: granules of cyanophycin, polyphosphates, glycogen in Cyanobacteria. Its thick cell wall allows it to withstand adverse conditions. They can germinate immediately after the formation, with no rest period, when placed in favorable conditions. In the absence of such conditions spores can survive for a long time.
Endospores. This structure resembles to the spore and found inside the cell hence called endospore. Endospores are small spores which develop asexually inside the bacterial cell. may be oval, ellipsoidal, spherical; in position: central, terminal, sub-terminal. Consist of Exosporium (EX), Spore coat (SC), Cortex (CX), Spore cell wall or core wall (CW), Core (Protoplast) (CR). Endospores are found in bacteria like Bacillus, Brevibacillus, Clostridium, Desulfotomaculum, Sporobacter, Sporomusa, Sporosarcina
Cells with specialized metabolic functions – nitrogen fixation
Heterocysts –thick coat, polar thylakoids, no nucleoid, lack of photosystem II
2) Bacteroides – are inside the knob, polymorphic, have leggemoglobin (binds oxygen)
Functions of resting forms
Preservation of DNA
2) Protect the population from the harmful effects of the environment
3) Are a way of transmitting infective host to host (pathogenic)
Spore structure the endospore structure is complex and consists of multiple layers which are: … Enumerate and describe
The endospore structure is complex and consists of multiple layers which are: 1. Exosporium (EX) - thin outer covering 2. Spore coat (SC) - composed of several protein layers - impermeable to most toxins and chemicals 3. Cortex (CX) - occupies most of the spore volume - made up from a unique, less cross-linked peptidoglycan 4. Spore cell wall or core wall (CW) - surrounds the protoplast or core 5. Core (Protoplast) (CR) - is metabolically inactive but contains ribosomes and DNA - contains DNA protecting acid-soluble DNA binding proteins - is dehydrated (explains high heat resistance) - contains DNA repair enzymes
-15% (in dry weight) of the molecule dipicolinic acid complexed with calcium
Endospores can survive environmental assaults that would normally kill the bacterium. These stresses include: …. The resistant nature is due to following reasons:…
Endospores can survive environmental assaults that would normally kill the bacterium. These stresses include:
high temperature,
high UV irradiation,
desiccation,
chemical damage and enzymatic destruction.
Some endospores have remained viable for more than 100,000 years!!
The resistant nature is due to following reasons:
1) Lowest metabolic activities.
2) Very few amount of water (cortex draws water).
3) Impermeable and protective nature of spore coat.
4) Lack of active enzymes.
5) High percentage of Ca+2 ion in spore composition.
6) Presence of stabilizer compound i.e. dipicolinic acid
Genetic Exchange in Bacteria are known to exchange genes in nature by three fundamental processes. Call them and explain why they are different from each other.
Bacteria are known to exchange genes in nature by three fundamental processes: transformation, conjugation, transduction.
Conjugation requires cell-to-cell contact for DNA to be transferred from a donor to a recipient. Two parental cells transfer their genetic material through a small tube like projection called conjugation tube.
Conjugation - commonest process of sexual reproduction in bacteria
In transformation, DNA is acquired directly from the environment, having been released from another cell. 3 steps of transformation: