Monera : Bacteria Cell Structure ,Nutrition , Respiration and Economic Importance
Monera:
It includes all the simple, primitive organisms which lack a well-developed nucleus and membrane-bound organelles.They contain circular double stranded naked DNA as the nuclear body in the cytoplasm.They are microscopic and made up of a prokaryotic cell.They are cosmopolitan in distribution and found in all type of habitat.Most of them have a rigid cell wall.They have an autotrophic and heterotrophic mode of nutrition.Reproduction is primarily asexual.The gas vacuole is present instead of true sap filled vacuoles.
The kingdom monera contains three major groups:
- Bacteria
- Cyanobacteria
- Archaebacteria
Bacteria
Occurrence:
Bacteria are found everywhere in air, soil, water. They are most adaptative organisms which can grow in very cold climate like arctic region, hot spring, desert, on and inside organisms body.
Characters:
- Bacteria are microscopic prokaryotic organisms.
- The incipient nucleus is present which lacks nucleolus and nuclear membrane. Chromatin body forms long naked circular DNA without histone protein which is also called nucleoid.
- Double membrane-bound cell organelles like mitochondria, endoplasmic reticulum, Golgi body, and plastids are absent.
- 70's type of ribosome is present.
- The cell wall is made up of muramic acid or peptidoglycan.
- Reserve food material is found in the form of lipid and glycogen.
- The gas vacuole is present.
- Flagella is a primitive type which is single stranded.
- Mode of nutrition is parasitic, saprophytic and autotrophic.
- Reproduction mainly takes place by binary fission.
- Sexual reproduction is almost absent if present it takes place by conjugation.
Types of bacteria:
On the basis of shape or morphology, bacteria are of following types:
Spherical bacteria( coccus or cocci):
Spherical bacteria are round-shaped bacteria. They lack flagella and are the smallest form of bacteria. It has different types they are:
Monococcus: They occur singlely.
Diplococcus: They are found in paired.
Tetracoccus: They are found in the group of four.
Streptococcus: They are found in a chain.
Staphylococcus: They are found in a cluster.
Rod- shaped bacteria(Bacillus):
They are short straight or slightly curved with a blunt end. Most of them contain flagella and few are without flagella. They are of following types:
Monobacillus: They are found in single.
Diplobacillus: They are found in a pair.
Streptobacillus: They are found in a chain.
Palisade: They occur parallelly.
Spiral bacteria (Helical):
Spiral bacteria are of following types:
Spirillum:
They are spirally twisted bacteria. They are larger in size than Bacillus and coccus. They contain flagella of one or both end.
Vibrio:
They are C-shaped or coma shaped bacteria. They contain single flagellum at one end.
Filamentous:
They are filamentous in shape. They have long thread-like(filamentous) structure.
Pleomorphic bacteria:
They can change their shape according to the environment. Eg; Azotobacter
Stalk bacteria:
They contain stalk. Eg: Caulobacter
Budding bacteria:
They have swollen structure at base end bud like outgrowth. Eg: Rhodomicrobacterium
Flagellation:
Flagella are small whips or hair like structures and acts as the organ of locomotion. Depending upon the presence and absence of flagella, the bacteria are of following types:
Atrichous: It is the type of bacteria without flagella.
Monotrichous: It is the bacteria having single flagellum at one end.
Amphitrichous: It contains single flagellum at both ends.
Cephalotrichous: It contains a group of flagella at one end.
Lophotrichous: It contains a group of flagella at both end.
Peritrichous: It contains a group of flagella found in all over the body surface of bacteria.
Gram positive and Gram negative Bacteria
| Gram positive(+) | Gram-negative(-) |
| They are those bacteria which retain the blue color of gram stain after they are washed with absolute alcohol. | They are those bacteria which lose the blue color of gram stain after they are washed with absolute alcohol. |
| The cell wall is thick, but lipid composition is less. | Cell wall is thin, but lipid composition is more. |
| The cell wall is single layered. |
Cell wall is double layered. |
| They are less resistant towards antibiotics. | They are more resistant towards antibiotics. |
| Few of them are pathogenic bacteria. | Most of them are pathogenic bacteria. |
| Eg; Bacillus, Clostridium |
Eg; Escherichia, Salmonella.
|
Cell Structure of Bacteria
The detailed structure of bacteria can be studied only under the electron microscope. The ultrastructure of bacterium reveals the following cell structure.
Mucilage layer:
It is the outermost layer present in the bacterial cell. If it is in the form of loose sheath then it is called slime layer and if it is found in the form of thick and tough sheath it is called capsule. It is made up of a type of polysaccharide. It is the protective layer. It protects the bacterial cell from drying, harmful chemicals acids, drugs etc.
Cell Wall
It is a rigid structure present inner to mucilage layer. It is made up of murein or peptidoglycan. It gives shape and structural support to the cell.
Protoplasm
It is differentiated into three parts;
Cell membrane
Cytoplasm
Nuclear body
Cell membrane:
It is a semi-permeable membrane present inner to the cell wall and works as outer covering layer of cytoplasm. It is made up of lipid, protein and a small amount of carbohydrate.
Cytoplasm
It is viscous, granular substance present between the cell membrane and nuclear body. It contains ribosomes, mesosome, chromatophore, extra circular DNA, RNA and food reserved material in the form of glycogen, lipid, and volutin granule. Double membrane-bound cell organelles like mitochondria, endoplasmic, reticulum, Golgi bodies and plastids are absent.
Nuclear body
The nucleus is an incipient type which lacks a well-organized nucleus. It lacks nuclear membrane and nucleolus which is also called nucleoid. DNA is long, double-stranded and without histone protein. Such DNA is also called naked DNA or circular DNA. DNA is commonly called bacterial chromosome. DNA carries all genetic information.
Extra circular DNA or plasmid is found in the cytoplasm which is a short fragment of circular DNA. It carries genetic information about fertility factor and resistance factor.
Ribosomes:
They are of 70s type. They are of two type;
- Free ribosome
- Fixed ribosome
Free ribosomes are found freely in the cytoplasm and fixed ribosomes are found attached to the cell membrane. It helps in protein synthesis. Sometimes the chain of ribosomes is found which are called polyribosomes.
Chromatophores
They are single membrane bound sac-like thylakoids which are found freely in the cytoplasm. Chromatophores are the site for photosynthesis. They are found only in photosynthetic bacteria.
Mesosomes:
They are finger-like infolding or projection of cell membrane. They increase the surface area for respiration. They contain respiratory enzymes. Mesosomes are present in gram-positive bacteria and absent in gram-negative bacteria. In gram-negative respiration occurs directly from the inner surface of cell membrane.
Gas vacuole:
The gas vacuole is found in bacteria. They help in floating in liquid.
Food reserved material is found in the form of lipid and glycogen. Volatingranule is also found which is inorganic granule and store phosphate.
Flagella
Flagella are the long fine thin thread like protoplasmic extension or appendages. They help bacteria to swim in liquid.
Pilli:
They are a short fine thin thread like protoplasmic appendages. They help in the attachment of bacteria with other at the time of conjugation.
Nutrition in Bacteria
Most of the bacteria do not contain chlorophyll. They are unable to synthesise their own food, but a small group of bacteria are capable of synthesising their own food. So, nutrition in bacteria is both autotrophic and heterotrophic.
Autotrophic
These bacteria can prepare their food by using raw materials and external energy. They are of following types:
Photoautotrophic:
They can prepare their food by using solar energy in the presence of photosynthetic pigment bacteriochlorophyll and chlorobium chlorophyll. Photosynthesis in bacteria differs from other green plants photosynthesis because there is no release of oxygen in photosynthesis. Such photosynthesis is called anoxygenic photosynthesis.
C02 ( or another compound)(+ H2S ? C6H12O6 + S ( Conditions required: Bacteriochlorophyll or chlorobium chlorophyll)
It is of following types they are:
Green sulphur bacteria
In this bacteria, the photosynthetic pigment is chlorobium chlorophyll and sulphur is by- product. Eg; Chlorobium
Purple sulphur bacteria
In this bacteria, the photosynthetic pigment is bacteriochlorophyll and sulphur are by- product. Eg; Chromatium
Non- sulphur bacteria
They have photosynthetic pigment bacteriochlorophyll and sulphur is not a by-product. Eg; Rhodopseudomonas
Chemoautotrophic
These bacteria prepare their food by using chemical energy in the absence of photosynthetic pigment. This process is called chemosynthesis. It is of following types:
Sulphur bacteria
They use chemical energy while there is oxidation of sulphur compound. Eg; Thiobacillus
2H2S or S2 + O2? 2S + 2H2O + energy
Iron bacteria
They use chemical energy while there is oxidation compound ( Fe2+? Fe3+). Eg; Leptothrix
4FeCO3 + O2+ 6H2O ? 4Fe(OH)3 + 4CO2+ Energy
Hydrogen bacteria
They use chemical energy while there is oxidation of molecular hydrogen. Eg; Pseudomonas
H2 + 1/202? H2O + Energy
Nitrifying bacteria
They use chemical energy while there is oxidation of nitrogen compound. Eg; Nitrosomonas, Nitrobacter
2NO2 + O2 ? 2NO3+ Energy ( Conditions required: Nitrosomonas)
Heterotrophic
These bacteria cannot prepare their food themselves. They obtain their food or nutrition from an outside source. It is of following types:
Parasitic
Parasitic bacteria live on and within other organisms(host) and they obtain their nutrition from the host. If the parasitic bacteria cause diseases and harmful for their host they are called pathogenic. If the parasitic bacteria cannot cause diseases and harmless for their host they are called non-pathogenic. Eg;
Cholera? Vibrio Cholerae
Pneumonia? Diplococcus pneumoniae
Saprophytic
These bacteria live and grow in dead and decaying organic matters and they obtain their nutrition from dead and decaying organic matters. Firstly they secrete decomposing enzymes which convert complex organic matter into simple and soluble form. These simple and soluble organic matters are absorbed by body surface of saprophytes. Eg; Pseudomonas
Symbiotic
Symbiotic bacteria live in close association with other living organisms so that they both are benefited to each other, neither of them is harmed. Eg; Rhizobium
Economic Importance of Bacteria
Bacteria have both harmful and beneficial effect. Both harmful and beneficial effect are described below.
Harmful effects
The harmful effects of bacteria are described below;
Spoilage of food:
Saprophytic bacteria decay or spoil our food, vegetables, jam, jelly, pickle bread. Eg; Pseudomonas
Food poisoning:
Food poisoning is caused by bacteria named as Clostridium botulinum.
Deterioration of Domestic articles;
Domestic articles like furniture, leather, cotton clothes etc are deteriorated by bacteria. Eg; Spirochaete cytophage
Diseases
About 90% of diseases are caused by bacteria. Eg; Vibrio cholera
Decreases soil fertility:
Some bacteria converts phosphate and nitrate in the form of free sulphur and nitrogen due to which fertility of the soil decreases. Eg; Defulfovibrio desulfurican, Thiobacillus denitrification
Useful effects
Nitrifying bacteria
Nitrifying bacteria like Nitrosomonas converts atmospheric ammonia gas in the form of nitride compound and another bacteria Nitrobacter converts nitride into nitrate form. These activities increase the fertility of the soil.
Nitrogen-fixing bacteria
Nitrogen fixing bacteria like Clostridium and Azotobacter are free living nitrogen fixing bacteria. They fix atmospheric free nitrogen into the nitrogenous compound. Rhizobium is symbiotically occurring nitrogen fixing bacteria. They fixed atmospheric free nitrogen into the nitrogenous compound. In this way, the fertility of soil can be increased.
Ammonifying bacteria
Saprophytic bacteria like Bacillus Vulgaris converts amino acid into ammonia gas in soil.
Industries
Dairy industries used lactobacillus in the preparation of lactic acid and Acetobacter used in the preparation of acetic acid likewise bacteria can be used in the preparation of alcohol.
Medicines
Bacteria can be used in medicine. Some antibiotics are prepared by using bacteria. Eg; Streptomyces Vitamin K and Vitamin B complex can be prepared by using bacteria.
Nature's Scavenger
Saprophytic bacteria decompose dead bodies and organic wastage and clean nature. This activity of bacteria balance ecosystem also. They are called as nature's scavenger.
Respiration in Bacteria
Both aerobic and anaerobic respiration occurs in bacteria.
Aerobic respiration
In aerobic respiration, respiration occurs in the presence of oxygen and a complete breakdown of glucose takes place in this respiration. It is of following types;
Obligate aerobic
There must be the presence of oxygen for obligate aerobic respiration. They die in the absence of oxygen. Eg; Bacillus subliles
Facultative aerobic
In facultative aerobic bacteria, respiration normally takes place by anaerobically but when there is a presence of oxygen they can change into aerobes. Eg; Rhodopseudomonas
Anaerobic respiration
In anaerobic respiration, respiration occurs in the absence of oxygen and incomplete breakdown of glucose takes place in this process.
Obligate anaerobic
In obligate anaerobic bacteria, respiration occurs anaerobically and they die in the presence of oxygen. Eg; Clostridium botulinum
Facultative anaerobic
In facultative anaerobic bacteria, respiration normally takes place by anaerobically but they can change into anaerobes in the absence of oxygen. Eg; Halophiles
Bug bounty – According to the online encyclopedia Wikipedia, the United States and India are the top countries from which researchers submit their bugs. India... Read Now
Bug bounty – According to the online encyclopedia Wikipedia, the United States and India are the top countries from which researchers submit their bugs. India... Read Now
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