This article discuss the eubacteria examples, their classification and detailed facts.
Domain Bacteria contains a single kingdom of eubacteria having some members of monera except archaebacteria. Eubacteria are modern in comparison to archaebacteria. All Eubacteria are prokaryotes. They are also called true bacteria.
Biological Classification of Eubacteria
Some Eubacteria examples are:
- Bacillus spp
- Clostridium spp
- Pseudomonas spp
- Escherichia coli
- Staphylococcus aureus
- Treponema dendicola
- Mycoplasma pneumoniae
- Mycoplasma hominis
- Mycoplasma salivarium
- Mycoplasma orale
- Mycoplasma bovigenitalum
Morphologically, they are not very complex, the tiny bacteria have complex biochemical, cytological and genetical characteristics. Their small size favours many charcteristics like fast cell division, resistant to environmental factors and ease to get nutrition or food from the surroundings.
They are found everywhere and well adapted to all type of habitats where organic matter is present. They inhabits our body starting from oral cavity to the end of alimentary canal. Dominantly, they lives in soil, water and air. Some are beneficial to humans and live in a mutualistic relationship while most of them are pathogenic in nature.
Some live as mutualist with plants or commensals in alimentary canal of animals. Some bacteria may remain viable when cold upto minus 1970C while some live upto 1000C.
Bacteria are unicellular prokaryotic microorganism having simple internal structure. They lacks all membrane bound organelles like mitochondria, golgi apparatus, lysosome, endoplasmic reticulum, chloroplast and true vacuole. They do not have nucleus but having structure without true membrane called nucleoid.
Structure of typical bacterial cell
The outermost layer in bacteria is mucilage sheath. The next layer is cell wall and inner layer is living cell membrane.
Components of a bacterial cell
Cell envelope– contains layer of mucilage (glycocalyx) +cell wall+ plasma membrane
Cytoplasm – matrix in the cell
Nucleoid– genetic material of the cell
Plasmid – circular extrachromosomal genetic material
Flagella – thread like structure used for the motility
Pilli and Fimbriae – outgrowth present on outermost layer used for exchanging genetic material between two bacterium.
Glycocalyx– if it is a loose covering in bacteria, it is called slime layer. If thick and tough then it is called capsule. Protective in function such as helps bacteria to reduce dehydration.
Cell wall – It is rigid and solid in nature, protects the cells from bursting in hypotonic solution. Madeup of peptidoglycan. Peptidoglycan is made up of two sugar derivatives NAG (N-acetyl glucosamine) and NAM (N-acetyl muramic acid).
Plasma membrane– It is selectively permeable and metabolically active. It takes part in cell wall synthesis and respiration. The gap between plasma membrane and cell wall is periplasmic space.
Mesosomes – it is formed due to inwards folding of plasma membrane.
Ribosomes – Small membraneless ribonucleoprotein having 70S dimension where S reperesents Svedberg. Generally are of two types : Free or scattered in cytoplasm and fixed or attached to plasma membrane. Ribosomes generally occurs in groups called polysomes.
Chromatophores – This special organelle is found in photoautotrophic bacteria which uses sunlight to produce their food. In Blue-green algae it is called chlorosomes. Chlorosomes contain photosynthetic pigments ( Bacteriochlorophyll, Bacteriophaeophytin and Carotenoid).
Nucleoid – True nucleus is absent, they have a single molecule of DNA having covalently joint ends. Genetic material is naked and without bounded by histone protein as they lacks membrane therefore it is also called prochromosome. Nucleoid is bound to plasma membrane directly or indirectly with the help of mesosome.
Plasmid- Extrachromosomal circular segments of DNA present in the cytoplasm of bacterial cell. Some plasmids which are transferable provides extra benefit to the bacteria. However they are not essential for their survival but gives strength to the bacteria to combat environmental stress.
Types of plasmid
- F plasmid (having fertility factor)
- R plasmid (provides resistance to antibiotics such as tetracycline, streptomycin and penicillin)
- Col- plasmid ( produce colicins or bacteriocins that kill other related bacteria).
Flagella – Fine protoplasmic threads which occur in number of bacteria for motility in a aquatic habitat. Some bacterial flagella possess antigenic properties (e.g. Salmonella)
Pili and Fimbriae – Pilli are protoplasmic outgrowth formed of protein pilin. They are also called sex pili which forms a bridge between two bacterium during conjugation.
Fimbriae are small bristle like structure which helps the bacteria to attach them to the solid surfaces or to attach with host tissue. Neisseria gonorrhoea attaches to urinary tract using fimbriae.
Examples of Bacteria
Bacillus spp :
Gram-positive obligatory aerobes. They mainly represent soil and rhizospheric bacteria. Diverse group of bacillus spp. contains pathogenic and non-pathogenic bacteria. e.g. Bacillus subtilis
Clostridium spp :
Gram-positive obligatory anaerobes or facultative anaerobes. They are capable of forming endospores. Strains of Clostridium causes illness by proliferating or by releasing toxins. e.g. Clostridium difficle
Pseudomonas spp :
Gram-negative bacteria. They are commonly found in soil and water. Many species of Pseudomonas like Pseudomonas aeruginosa causes illness in humans like pneumonia. People acquire Pseudomonas mainly from nosocomial.
Escherichia coli :
Gram-negative, common intestinal pathogen. They have large diverse group of bacteria. Most of the strains of this bacteria are harmless but many are pathogenic i.e., secretes endotoxin. Responsible pathogen for causing UTI.
Soil dwelling and Symbiotic bacteria found in the root nodules of leguminous plants. Nodules forms by exchanging the chemical signals between plant and bacteria. Flavanoids secreted by plants activates the nod genes of rhizobia causes root hair curling and forms the bacteroids in nodule which fix atmospheric nitrogen using the enzyme nitrogenase.
Staphylococcus aureus :
Gram-positive ,found commonly on human skin and upper respiratory tract. They can be transmitted from one person to another directly or by fomites. Hospital patients and staff are most likely to acquire the colonization of Staphylococcus aureus.
Treponema dendicola :
Parasitic bacteria lives inside human body.
Mycoplasma or Mollicutes
Mycoplasma are wall-less pleomorphic gram-negative prokaryotes with smallest size 0.1-0.15μm. The term MLO (Mycoplasma like organism) is used to denote the parasitic nature in plants. While PPLO (Pleuropneumonia like organism) are parasites in animals.
Shape – coccoid, coccobacillar, helical, stellate, unbranched or branched filament.
Habitat –They are anaerobic in nature and mostly prefer to live as saprophytes in soil or parasites in humans or animals.
Cell membrane- They lacks cell wall
Mesosome – Mesosome is absent. Reproduction is by binary fission.
Mycoplasma are treated with tetracyclines. As it is deficient in cell wall, penicillin has no effect on it.
Examples of Mycoplasma
Mycoplasma pneumoniae :
Primary atypical pneumonia. Generally affects the lungs and lining of respiratory tract. Affected person can spread the bacteria in the environment by coughing or sneezing.
Mycoplasma hominis :
It is a common inhabitant of male and female genital tract. As mycoplasma do not have cell wall, so it becomes quite difficult to cure the ailment because most of the cell wall targeting antibiotic like penicillin does not work.
Mycoplasma salivarium :
This bacterium is mostly associated with eye, oral and ear disorders. It also plays a important role in slow down the immune response to other pathogens.
Mycoplasma orale :
Intracellular, opportunistic pathogen causes illne in immunocompromised patients. They are mostly found in human oral cavity.
Mycoplasma bovigenitalum :
Causes inflammation of genitals in cattle.
Cyanobacteria (Blue-green algae)
Cyanobacteria are gram-negative oxygenic photoautotrophs which have a prokaryotic organisations. They are also known as blue-green algae, myxophyceae and cyanophyceae.
- They have naked DNA which is compacted to form nucleoid like structure.
- Protective mucilage occurs over the cells.
- Absence of membrane-lined organelles, presence of 70S ribosomes.
- They have ability to do chromatic adaptation.
- Flagella and cilia are absent.
- Chromoplasm contains thylakoids.
- Thylakoids contain small structures called phycobilisomes.
- They contain photosynthetic pigments (chlorophyll a, carotenoids and phycobillins).
- They store food reserve in the form of lipid globules, cyanophycean starch,and cyanophycin granules.
- They perform nitrogen fixation by creating anaerobic conditions in a special cells called heterocysts.
Examples of Cyanobacteria
Contain single filament. It causes asthma and gastro-intestinal problems by its toxins. Species of Oscillatoria are seen to clog water filters thereby obstructing supply of drinking water.
Perform nitrogen fixation and have heterocyst. They increase nitrogen fertility of rice fields and provide certain growth promoting chemicals to crop plants.
It is a colonial filamentous cyanobacterium found in both aquatic and moist terrestrial habitats. Nostoc colonies are often called moonspits, fallen stars or star jelly.
They are found in moist soil, rocks, bottom of the lake and also rarely found in marine habitat. They secrete chemicals which are toxic to mosquito larvae.
They are rich in minerals, protein, vitamins and essential fatty acids. It strengthens immune system and builds blood. It also possesses anticancer and antiviral properties. Spirulina has soft muco polysaccharides and no cellulose in the cell wall so it is can be digested easily and used as SCP (single cell protein).
Actinomycetes are gram-positive bacteria with high G+C DNA. Formerly called Ray fungi. They form branching network of filaments or hyphae and produce spores which resembles fungi like structure.
An important characteristics of these bacteria is they can easily utilize the variety of substrates and some less degradable substrate like cellulose, chitin and hemicellulose.
They have special ability to synthesize secondary metabolites.
Shape – shape can be varied according to the classification: occur as rods, cocci, branched filaments, form aerial mycelium
Habitat – Soil, marine, found in compost and related materials
Importance – Actinomycetes have great importance in biotechnology as they are potential producer enzymes, antimicrobials, enzyme inhibitors, immunomodifiers and growth promoting substance for plants and animals.They secrete large number of antibiotics inlcuding beta lactams, aminolgycosides, chloramphenicol, macrolides etc.
Examples of Actinomycetes
They are aerobic, gram-positive mainly found in the soil forms filaments or mycelium. They have high G+C DNA. e.g. Streptomyces avermitilis which is used in the production of antiparasitic medicine like Ivermectin.
Mostly aerobic and Gram-positive bacteria. Most of the species are commensal in nature like Corynebacterium diptheriae which causes diptheria (ailment caused by inflammation of mucous membrane which hinders the swallowing and breathing process.
Gram-positive slow growing bacteria. They contain mycolic acid in their cell wall due to which require special staining technique (ZN staining) to identify them. They have a high G+C content. Mycobacterium tuberculosis is mainly responsible for causing TB in patients.
They are gram-positive bacteria having aerial mycelium with spores in a chain. e.g. Actinomadura madurae
FREQUENTLY ASKED QUESTIONS
Q1. Define Prochromosome.
Prochromosome is called the nuceoid of prokaryotes formed by joining the strands of DNA covalently without histone proteins.
Q2. What is Chromatic adaptation?
Cyanobacteria contain pigments, they can change their pigmentation according to the wavelength of light received by it. Oscillatoria looks green in red light, , yellowish in bluish-green light, red in green light and bluish-green in yellow light.
Q3. What is Heterocyst?
It is a specialized structure found in filamentous cyanobacteria. Heterocyst are thick walled and pale yellow in colour used for fixing nitrogen in the absence of oxygen. It is present between two vegetative cell i.e., intercalary
Q4. What is phycobilisome?
Phycobiliosme is a phycobilin (water soluble, protein bound accessory photosynthetic pigment) containing granular structure that is attached to thylakoid surface in cyanobacteria and red algae.