Bacteria are prokaryotic cells that contain unique rRNA sequences different from Archaea and Eukarya. They are encapsulated with cell membranes composed of peptidoglycan and unbranched fatty acid chains attached to glycerol molecules by ester linkages.
The different domain bacteria examples are as follows
- Aquificae
- Thermotogae
- Thermodesulfobacteria
- Deinococcus
- Chrysiogenetes
- Chloroflexi
- Nitrospira
- Deferribacteres
- Cyanobacteria
- Chlorobi
- Proteobacteria
- Firmicutes
- Actinobacteria
- Planctomycetes
- Chlamydiae
- Spirochaetes
- Acidobacteria
- Bacteroidetes
- Fusobacteria
- Fibrobacterota
Aquificae
The phylum Aquificae is considered the oldest branch of bacteria.
Aquifex pyrophilus is a Gram-negative rod-shaped, microaerophilic bacterium. This thermophilic bacterium can thrive in temperatures ranging from 85°C and 95°C. Aquifex is a lithoautotroph that utilizes hydrogen, thiosulfate, and sulfur along with oxygen as terminal electron acceptors.
Thermotogae
The second oldest branch is the phylum Thermotogae. This phylum includes Gram-negative, rod-shaped thermophiles enclosed in an envelope that is extended from both the ends as a balloon. They flourish actively in geothermal regions.
Contrastingly, Thermotogae is a chemoheterotroph that can survive anaerobically on carbohydrates and protein.
Thermodesulfobacteria
These are sulfur reducing bacteria that utilizes sulfate as electron acceptor for anaerobic respiration. These bacteria can breathe sulfate. Example Thermodesulfobacterium hydrogeniphilum is thermophilic sulfate-reducing bacteria.
Deinococcus
This group of bacteria is highly resistant to gamma rays and UV radiation. They have thick cell walls and can inhabit outer space for years. They have characteristic carotenoid pigment deinoxanthin which gives the bacterium pink color.
Deinococcus radiodurans is an important member of this phylum. It is a poly-extremophilic, non-endospore-forming bacterium that derives energy from organic compounds.
Chrysiogenetes
Chrysiogenes arsenatis is a member of this class that uses arsenate as a terminal electron acceptor. These anaerobic bacteria are usually found in arsenic-contaminated soils. They appear as rod-shaped motile cells with a single flagellum. They reduce arsenate to arsenite. It can utilize acetate, pyruvate, lactate, malate, and fumarate as its carbon source.
Chloroflexi
This phylum is now referred to as Chloroflexota which includes aerobic thermophilic bacteria, and anoxygenic phototrophs. They have a single membrane but appear as gram-negative after staining. These are green non-sulfur anoxygenic photosynthetic bacteria, that contain BChl a and c/d and carotenoids such as carotene, β—carotene, and myxocoxanthin as major photosynthetic pigments.
Nitrospira
It is a gram-negative bacterium that is capable of nitrite oxidation. It is helical in morphology and remains in aggregates. This chemolithoautotrophic bacterium is used in sewage water plants and reduces the emission of greenhouse gases. As it contains nitrite oxidoreductase genes thus it is mentioned as a nitrite oxidizer.
Deferribacteres
This group contains gram-negative anaerobic bacteria. They are rod-shaped and use iron, manganese, and nitrate for respiration. Geovibrio is a non-sporulating member of this class that uses sulfide, formate, and acetate as electron donors while sulfur, nitrate, and fumarate as electron acceptors.
Cyanobacteria
This group is the most diverse group of bacteria which contains about 2000 and more species. These gram-negative bacteria are also known as blue-green algae.
Cyanobacteria use chlorophyll a and photosystem I and II. The carbon reserve is glycogen and contains phycocyanin and phycoerythrin as pigments necessary for light reactions. These pigments are stored in specialized organelles called phycobilisomes which are similar to chloroplasts of plants.
Some important cyanobacteria are as follows
Nostoc
These are filamentous cyanobacteria distributed in both terrestrial and aquatic ecosystems. It is often involved in symbiotic interaction with plants and helps in nitrogen fixation. These bacteria have heterocyst, a specialized cell responsible for nitrogen assimilation. Nostoc is widely used as a biofertilizer.
Anabaena
Anabaena is another important genus of the cyanobacteria group that helps in nitrogen fixation. They contain heterocysts that convert nitrogen to organic ammonia and are often used as a biofertilizer in paddy fields.
Spirulina
This genus is a worldwide famous group of cyanobacteria which is referred to as superfood. It doesn’t contain a heterocyst. However, Spirulina is very popular as a dietary supplement as it stores a high amount of protein (65-70%). It is rich in chlorophyll and carotenoids which act as antioxidants and contain vitamins such as folic acid, Vit B2, and Vit B12 along with other necessary minerals.
Chlorobi
Representative members of this group are Chlorobium tepidum and Chlorobium vibrioforme. They are anaerobic photoautotrophs, green sulfur bacteria that utilizes reduced sulfur compounds for electrons and performs non-cyclic photosynthesis. They contain BChl c, BChl d, and BChl e.
Proteobacteria
Proteobacteria is also known as Pseudomonadota. This phylum includes gram-negative bacteria that perform anoxygenic photosynthesis.
- Alpha proteobacteria
- Beta proteobacteria
- Gamma proteobacteria
- Delta proteobacteria
- Epsilon proteobacteria
- Zeta proteobacteria
Alpha proteobacteria
The major photosynthetic pigments are BChl a/b and carotenoids such as lycopene, and rhodopsin. They utilize reduced hydrogen and sulfur compounds as electron donors and use photosystem II for photosynthesis.
Methylobacterium | Can utilize C1 compounds, normally present in soil and water, facultative-aerobe |
Rhizobium | Nitrogen-fixing soil bacteria associated with Leguminosae plant, motile cells |
Caulobacter | Heterotrophs and oligotrophs with rod or vibrio shaped cells |
Agrobacterium | Plant pathogen causes tumors, chemoorganotroph, aerobic motile non-sporing rods |
Rickettsia | Obligate intracellular parasites, pleomorphic |
Brucella | Pathogenic, coccobacillus with flagella |
Coxiella | Obligate parasites causes Q fever |
Rhodospirillum | Photoheterotrophs either aerobic or anaerobic |
Beta proteobacteria
These purple non-sulfur bacteria contain bacteriochlorophylls and carotenoids as major photosynthetic pigments. They can survive in a wide range of environments by using various metabolic strategies. They make use of reduced nitrogen and sulfur forms as electron donors.
Bordetella | Aerobic, nonmotile, coccobacillus parasites of mammals, need organic sulfur and nitrogen |
Neisseria | Pathogenic causes gonorrhea and meningitis, oxidases-positive, resident of mucosal membranes of mammals |
Burkholderia | Aerobic, straight rods with a single flagellum, with Poly-β-hydroxybutyrate as reserve material, causes cystic fibrosis |
Leptothrix | Aerobic straight rods covered with a sheath containing iron and manganese oxides, present in clogged pipes |
Nitrosomonas | Ammonia-oxidizing, obligate chemolithoautotroph |
Thiobacillus | Autotrophs, produce sulfate by oxidizing H2S, beneficial for plants |
Gamma proteobacteria
Azotobacter | Aerobic bacterium, form cysts and helps in nitrogen fixation |
Escherichia | Facultatively anaerobic in nature, oxidase-negative, converts formic acid to H2 and CO2, common parasites for mammals |
Methylococcus | Methane-utilizing aerobic bacterium, usually form cysts |
Haemophilus | Facultative or aerobic, oxidase-positive, fermentative bacterium, frequently present as parasites of mammals |
Pseudomonas | Chemoheterotrophs with aerobic respiration, common pathogens for animals and plants |
Delta proteobacteria
Bdellovibrio | This is an aerobic pathogenic bacterium that grows in the periplasmic space of other gram-negative bacteria. |
Desulfovibrio | Sulfur-reducing bacterium that inhabits polluted lakes and sewage lagoons |
Desulfuromonas | Sulfur-reducing bacterium mostly present in anoxic freshwater environments |
Myxococcus | Aerobic, motile bacterium usually present in soil and remain as dormant myxospores. These are micro predators and secret various digestive enzymes to lyse other bacterial cells. |
Epsilon proteobacteria
These are gram-negative rod-shaped microaerophilic proteobacteria.
Campylobacter | This genus comprises both pathogenic and non-pathogenic members. These are fermentative oxidase-positive bacteria often found in the intestinal tract and oral cavity of animals. |
Helicobacter | These are both catalase and oxidase-positive, usually found in the gastrointestinal tract of humans. |
Zeta proteobacteria
This group is represented by Mariprofundus ferrooxydans. This bacterium is found in deep sea specially at hydrothermal vents as iron-oxidizing microorganism.
Firmicutes
This phylum contain gram-positive bacteria. Based on 16S rRNA analysis, this phylum contains bacteria with low G+C content.
Class : Mollicutes | |
Acholeplasma | Mostly present in vertebrates, with optimum temp 30-37°C |
Anaeroplasma | Inhabit rumen of bovine and anaerobes |
Entomoplasma | Usually present in insects and plants with optimal growth at 30°C |
Mycoplasma | Present in humans and animals with 37°C optimal temperature, require sterol for its growth |
Spiroplasma | Helical filaments grow at 30-37°C in insects and plants |
Ureaplasma | Capable of hydrolysis of urea, present in human and animal |
Class : Clostridia | |
Clostridium | Anaerobic, chemoorganotrophs with oval or spherical endospores, rod-shaped pleomorphic, catalase negative |
Heliobacterium | Anaerobic, photoheterotrophs with BChl g |
Class : Bacilli | |
Bacillus | Aerobic or facultative chemoorganotrophs with straight rod-shaped, have endospores, catalase-positive |
Enterococcus | Facultative spherical or ovoid cells, catalase-negative and undergoes fermentation, produce lactate with any gas, present in fecal matter |
Lactobacillus | Facultative or microaerophilic, non-sporing, fermentative, catalase-negative |
Staphylococcus | Chemoorganotrophs, catalase-positive, pathogenic, present in the skin and mucosal membrane of humans |
Streptococcus | Fermentative, produce lactate without any gas, catalase-negative, hemolysis-positive, parasites of animals |
Actinobacteria
This is a fascinating group of bacteria that produces characteristic secondary metabolites with anticancer, and anti-helminthic properties. Their life cycle involves the development of filamentous hyphae that carry spores.
Arthrobacter | Aerobic, present as rod-shaped cells (young) or small cocci (old), catalase-positive, mostly present in the soil |
Corynebacterium | Facultatively anaerobes, fermentative, oxidase-positive |
Micrococcus | Aerobic, present as tetrads or irregular cocci, catalase-positive, mammalian skin resident and also present in soil |
Mycobacterium | Aerobic, slightly curved rods, catalase-positive, present in soil and water, sometimes pathogenic in nature |
Streptomyces | Aerobic, branched vegetative mycelium with aerial mycelium containing spore, can utilize various organic compounds |
Frankia | Aerobic or microaerophilic, branched vegetative mycelium with no aerial mycelium, usually present as symbionts with plants |
Planctomycetes
This group of bacteria is widely distributed in both aquatic and terrestrial environments. They play a significant role in carbon and nitrogen cycles and can survive under limited carbon and nitrogen sources. They lack the peptidoglycan layer and have separate internal compartments.
These anaerobes are capable of oxidizing ammonia to nitrogen inside a specialized organelle called anammoxosome which bears similarities with eukaryotic mitochondria.
Chlamydiae
This group comprises obligate intracellular parasites; some are pathogenic while others remain as symbionts of humans and animals. It also lacks a peptidoglycan layer. Example Chlamydia pneumoniae which causes pneumonia, and Chlamydia trachomatis that causes chlamydia.
Spirochaetes
These are double membraned gram-negative bacteria with distinct corkscrew shapes. This group has distinct flagella known as endoflagella that is anchored at the end of the bacteria cell. It has a twisting motion. Most of the species are pathogenic in nature.
Acidobacteria
This phylum represents gram-negative, acidophilic soil bacteria. Mostly present in hot springs and metal contaminated soils. In soil, it represents 52% of the total soil bacteria community. It contains bacteriochlorophyll a and carotenoids such as Echinenone, lycopene, ɣ- and β- carotene. It utilizes organic compounds such as acetate and succinate as electron donors
Bacteroidetes
These can be either pathogenic or symbiotic bacteria. These are gram-negative, rod-shaped bacteria. Some species can degrade complex polysaccharides of plants such as starch, and cellulose. They exhibit protease and urease activity.
Fusobacteria
These are obligate anaerobes with rod-shaped morphology. Species of this phylum colonizes the mucosal membrane of the humans and causes tonsilitis and peritonsillar abscess.
Fibrobacterota
This phylum includes bacteria that are capable of degrading cellulose and usually present in the rumen of bovine animals. This phylum is represented by two members Fibrobacter succinogenes and Fibrobacter intestinalis.
Summary
Domain bacteria comprises a diverse group of micro organisms that utilizes various metabolic strategies. Through such metabolic processes, these can thrive anywhere starting from deep sea hydrothermal vents to outer space. They can utilize organic and inorganic carbon sources. Some are pathogenic, commensal while others are beneficial to plants.
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I am a doctoral student of CSIR- CIMAP, Lucknow. I am devoted to the field of plant metabolomics and environmental science. I have completed my post-graduation from the University of Calcutta with expertise in Molecular Plant Biology and Nanotechnology. I am an ardent reader and incessantly developing concepts in every niche of biological sciences. I have published research articles in peer-reviewed journals of Elsevier and Springer. Apart from academic interests, I am also passionate about creative things such as photography and learning new languages.
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