Bacteria is a group of microscopic, single-celled microorganisms that inhabit virtually all environments, including water, soil, organic matters, and the bodies of plants and animals.
Classifying bacteria on the basis of their morphology is extremely difficult; bacteria are generally quite small and have simple shapes, though there are some bacteria, notably the cyanobacteria and actinomycetes, with sufficiently complex morphology to permit classification by shape. In addition to shape, bacteria have traditionally been identified and classified on the basis of their biochemistry and the conditions under which they grow. The advent of molecular biology has made it possible to classify bacteria on the basis of similarities among DNA sequences.
Domain Bacteria contains 5 major groups: proteobacteria, chlamydias, spirochetes, cyanobacteria, and gram-positive bacteria.
The proteobacteria are subdivided into five groups, alpha through epsilon. Species in these groups have a wide range of lifestyles. Some are symbiotic with plants, others live in hot vents deep under the sea, and others yet cause human diseases
Bacteria of Phylum Proteobacteria
Some species are photoautotrophic but some are symbionts of plants and animals and others are pathogens. Eukaryotic mitochondria are thought be derived from bacteria in this group.
|Rhizobium: Nitrogen-fixing endosymbiont associated with the roots of legumes.
Rickettsia: Obligate intracellular parasite that causes typhus and Rocky Mountain Spotted Fever (but not rickets, which is caused by Vitamin C deficiency)
This group of bacteria is diverse. Some species play an important role in the nitrogen cycle.
|Nitrosomonas: Species from this group oxidise ammonium into nitrite
Spirillum minus: Cause rat-bite fever.
Many are beneficial symbionts that populate the human gut, but others are familiar human pathogens. Some species from this sub group oxidize sulfur compounds.
|Escherichia coli: Normally beneficial microbe of the human gut, but some strains cause disease.
Salmonella: Certain strains causes food poisoning or typhoid fever.
Yersenia pestis: Causative agent of Bubonic plague.
Psuedomonas aeruginosa: Causes lung infections.
Vibrio cholera: Causative agent of cholera.
Chromatium: Sulfur- producing bateria that oxidise sulfur, producing H2S.
Some species generate a spore-forming fruiting body in adverse conditions. Others reduce sulfate and sulfur.
|Myxobacteria:Generate spore-forming fruiting bodies in adverse condition.
Desulfovibrio vulgaris: Anerobic, sulfate reducing bacterium.
Many species inhabit the digestive tract of animals as symbionts or pathogens. Bacteria from this group have been found in deep-sea hydrothermal vents and cold seep habitats.
|Campylobacter: Causes blood poisoning and intestinal inflammation.
Helicobacter pylori: Causes stomach ulcers.
The other four major groups of bacteria are similarly diverse. Chlamydias are pathogens that live inside host cells, while cyanobacteria are photosynthesizers that make much of earth’s oxygen. Spirochetes include both harmless bacteria and harmful ones, like the Borrelia burgdorferi that cause Lyme disease. The same is true of Gram-positive bacteria, which range from probiotic bacteria in yogurt to the Bacillus anthracis that cause anthrax.
All members of this group are obligate intracellular parasites of animal cell. Cell walls lack peptidoglycan.
|Chlamydia trachomatis: Common sexually transmitted disease that can lead to blindness.|
Most members of this species, which has spiral-shaped cells, are free living anaerobes, but some are pathogenic. Flagella run lengthwise in the periplasmic space between the inner and outer membrane.
|Treponema pallidium: Causative agent of syphilis
Borrelia burgdorferi: Causative agent of Lyme diseases.
Also known as blue-green algae, these bacteria obtain their energy through photosynthesis. They are ubiquitous, found in terrestrial, marine and fresh water environments. Eukaryotic choroplasts are thought be derived from bacteria in this group.
|Prochlorococcus: Believed to be the most abundant photosynthetic organism on the earth; responsible for generating half the world’s oxygen.|
Soil-dwelling members of this subgroup decompose organic matter. Some species cause disease. They have a thick cell wall and lack an outer membrane.
|Bacillus anthracis: Causes anthrax
Clostridium botulinum: Causes Botulism
Clostridium difficile: Causes diarrhea during antibiotic therapy.
Streptomyces: Many antibiotics, including streptomyocin, are derived from these bacteria.
Mycoplasmas: These tiny bacteria, the smallest known, lack cell wall. Some are free-living and some are pathogenic.