Bacteria are the microorganisms on the earth with unique features.
The external and internal characteristics of bacteria are a bit different from rest of the organisms on the earth.
They are prokaryotic in nature meaning they are earliest forms of cell without nucleus.
These characters make them immortal, omnipresent and also very versatile.
They are useful to nature, man and life on earth, Though some of them can cause diseases to humans.
Unique & Distinguishing Characteristics of bacteria
1. No nucleus: Unlike other eukaryotic cell, bacterial cell is the only cell which lacks prominent nucleus within. This feature has lead to the scientists to consider bacteria as primitive organisms i.e earliest forms of life on earth.
2. Presence of Cell wall: Bacteria has a cell wall which is distinct from other cells having cell wall. The wall is made of different substances like glycoproteins, lipopolysacharides and lipoproteins.
3. Cell membrane: This is present immediately below the cell wall. This has a small variation with that of plants and animals cell membranes. In plants and animals, it is mostly a single or double layer (bi-layer) of lipids. But bacteria especially the gram negative ones have an extra membrane i.e. an outer membrane called periplasm which lies bellow cell wall but above cell membrane.
4. Pilli: These are small and tube like projections from bacterial surface. They are the organelles of sexual reproduction and are involved in exchange of genetic material as part of reproduction between two bacteria.
5. Food dependence: All the organisms either live by their own or on other resources. But bacteria have different modes of food procurement. Some of them synthesize their own food like plants by use of sunlight.
Few of them are parasites which live on alive plants and animals. They cause diseases to the host in doing so.
Many bacteria are saprophytes which means, they live on dead and decaying matter.
While others are symbiotic. They live in a give and take relationships with other animals. Ex: rhizobium in roots, E-coli in intestine.
6. Reproduction: Most organism have one or two methods of reproduction. But bacteria have many.
a. Asexual reproduction: The bacteria cell undergoes to produce two bacteria by Binary fission and also by endospores.
b) Sexual reproduction:It is also by two distinct methods like transformation, conjugation and transduction. In transformation, one bacteria releases naked DNA strand into the surroundings. The other bacteria takes t up and incorporate into their genome. Transduction happens due to virus.
Read how do bacteria reproduce for more details.
7. Spore formation: When the environmental conditions around are harsh, the bacteria converts to a hard spore form. This spore is highly resistant to heat, chemicals and drought conditions.
When the conditions are favorable, these spores break open and release the bacteria.
8. DNA Gyrase: Gyrases are the enzymes involved in DNA transcription. They perform, nick and joint function in the DNA chains. They cut the strands, induce negative super-coils and also join the cut ends after the process. In Humans and other mammals, instead of DNA gyrase, there is DNA topoisomerase-II for similar function.
9. Ribosomes: The protein making machinery has 70S ribosome which is of two sub-units as 50S and 30S. While in other animals and plants, it is 80S ribosome consisting of two sub-units 60S and 40S.
10. Absence of Cell organelles: Other cell organelles like mitochondria, golgi bodies, endoplasmic reticulum are absent in a bacterial cell.
11. Flagella presence: Some of the bacteria are motile. They, especially the bacilli type have flagella. These are the organs of locomotion. They are long filamentous organs originating from cell membrane. You can learn more about flagella at bacteria classification. They are classified based on the number and arrangement of flagella on the cell.
12. Bacteria shape: The shape of bacteria is very characteristic to them. It is also easy for identification of bacteria by recognition of shapes. These bacterial structures have specific shape like stick (bacilli), spherical (cocci), coma (cholera bact.), spiral (spirochete), in a bunch or isolated etc.
13. Cosmopolitan distribution: Bacteria are the only organisms which show cosmopolitan distribution. They are present in air, water, soil, snow etc. They are present at very cold (minus degree) temperature regions and also very high temperature regions. They can live in acidic environment (helico bacter pyroli) and even basic environment (iron bacteria).
14. Resistance and tolerance: Some of the bacteria are highly resistant to adverse environments. Even they get tolerance to harsh chemical and other stuff which destroy them. Hence irrational use of antibiotics. THis has become so severe that World Health Organization warns of rampant prevalence of resistant bacteria which can be incurable by currently available drugs.