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Bacteria are the microorganisms with single cells and are prokaryotes. These are most primitive unicellular microorganisms and are not enclosed in a nuclear membrane of the cell. Several number of bacterias are present everywhere like in water, air, food stuff or soil and even inside the human body like in genital tracts, in mouth, in intestines or in mouth etc. Bacteria are the microorganisms which upto some extent are useful in some cases; for example: in the intestine it is beneficial because it helps in synthesizing some vitamins like vitamin B while some of them are harmful or toxic which may cause disease to the living beings.
Size: Bacteria are one of the smallest living microorganisms having average size of approximately 0.5 micrometers thick and 2 micrometers long.
Structure of Bacteria
The structure of bacteria is described below;
It consists of the protoplasm/protoplast, the living substance which lies within the cell membrane (cytoplasm + bacterial chromosomes) and is surrounded by a cell wall (non-living stiff wall).
The thin cell membrane lies beneath the cell wall and surrounds the cytoplasm (gelatinous substance which contains ribosomes and genetic material).
The cell wall is the layer which is made up of peptidoglycan (a polymer) and is situated outside to that of plasma membrane [Gram positive bacteria have thick cell wall].
The chromatin (DNA) material is present in the central region which consists of the genetic information and it is in the form of a single circle and is not enclosed in a nuclear membrane but at some point it is attached to the cell membrane.
The cytoplasm contains granules, vacuoles and sometimes pigment.
A slimy protective layer outside the cell wall called a capsule is present.
It contains ribosomes where the proteins are synthesised.
Flagellum is the part which is responsible for the movement.
It also contains pilli (hair like structure) which helps in transferring the genetic material from one cell to another.
Types of Bacteria
The types of bacteria on the basis of their shape are as follows;
Cocci: It is a spherical shape bacteria which is further divided into diplococci (pair), streptococci (long chain bacteria) and staphylococci (cluster like structure). For example; pneumonia is caused by bacteria named Streptococcus pneumoniae.
Bacilli: It is rod shaped bacteria which may be single or a long chain.
Spirilla: It is a spiral or twisted bacteria and is a single bacteria.
Vibrio: It is a comma shaped bacteria. For example; cholera is caused by bacteria named Vibrio Cholerae.
The types of bacteria on the basis of staining are as follows;
Gram positive bacteria: This type of bacteria gives stain and a violet color is obtained on staining when observed under microscope. It has a peptidoglycan type cell wall.
Gram negative bacteria: This type of bacteria only exhibits the counterstain and a red color is obtained on staining when observed under microscope. It has a lipopolysaccharide type cell wall.
The types of bacteria on the basis of mode of nutrition are as follows;
Heterotrophic bacteria: for example, cyanobacteria. It subdivided into saprotrophic (drawing nourishment from decaying dead organisms) and parasitic (drawing nourishment from the body of their living hosts).
Autotrophic bacteria: for example; disease causing bacteria.
The types of bacteria on the basis of their mode of respiration are as follows;
Aerobic Bacteria: for example; mycobacterium.
Anaerobic Bacteria: for example; actinomyces.
Reproduction of Bacteria
Asexual reproduction is the only way to reproduce the bacteria and is done by means of cell division or fission. The circular DNA duplicates due to which the cell expands and the two DNA are pulled apart. The cell now constricts at the middle which will separate the two cells and depending upon the bacteria type, the 2 daughter cells may either separate from each other as independent cells or remain attached to each other. It is of two types;
Highly primitive type of sexual reproduction.
Spores to overcome unfavorable conditions.
Conclusion
A bacteria is a single cell microorganism which does not have chlorophyll. Bacteria are used in medicine in the production of antibiotics, vaccines and serums. It is also used in agriculture as nitrogen fixing bacteria etc. These are the most primitive form of living organisms and most of them are heterotrophic in nature which form spores to overcome the unfavorable conditions. It is useful in decay, nitrification, vitamin synthesis, cellulose digestion, fermentation and many more.
