Eubacteria (true bacteria)

Back to Classification of Life

Bacteria typically have a cell wall outside the plasma membrane; it most commonly consists of peptidoglycan. Flagella may be present but have a different structure from those of the eukaryotes. Pili may occur; these are tubular extensions for attachment and the exchange of genetic material. Although there are nochloroplasts, photosynthetic membranes may be present. Sexual reproduction does not occur: the cells simply divide by binary fission, although exchange of genetic material in the form of plasmids is possible.

Bacterial taxonomy is in ferment because of the advent of new, molecular techniques of classification. A useful traditional classification is based on size and shape, which can be studied in bacteria that have been dried, fixed and stained with crystal violet. Bacteria can be divided into two groups according to whether they retain this stain (Gram positive) or not (Gram negative). Many gram-positive bacteria are important in the production of foods, including yoghurt and other milk products. Of historical interest is the production of acetone and butanol by means of a species of Clostridium; it was used in the production of explosives and synthetic rubber in the run-up to the First World War at the beginning of the twentieth century. Members of the genus Streptomyces are famous for their synthesis of a wide range of antibiotics, including penicillin.

Although most gram-positive bacteria are harmless, some are pathogenic to humans. These include members of the genus Streptococcus, various species being responsible for sore throats, pneumonia and dental caries. Staphylococcus causes pimples, boils, wound infections and other diseases, as well as spoiling food. A multiple-drug-resistant form of Staphylococcus causes a virulent form of septicaemia (‘blood poisoning’). Clostridium is a genus of bacteria that produce spores as part of the life cycle. Bacteria of this genus are associated with food spoilage and botulism. As the spores germinate, they produce neurotoxins which, if ingested, leads to paralysis and either respiratory or cardiac failure. A very important disease-causing bacterium in the Western Cape is Mycobacterium tuberculosis, the bacterium that causes TB. TB is reaching epidemic proportions, especially in the Western Cape, and drug-resistant strains are now common.

Gram-negative bacteria include Rhizobium, which grows symbiotically in the root nodules of legumes and fixes atmospheric nitrogen; legumes can thus be grown in crop rotations and ploughed into the soil to increase nitrogen levels. Thiobacillus is important in the mining industry, as it produces sulphuric acid, which degrades the matrix containing the ore, thus solubilizing the gold or copper. The light emitted by the light organs of certain fish is actually caused by bacteria such as Vibrio fischeri; in contrast, Vibrio cholerae is the pathogen responsible for cholera. Food contaminated with Salmonella typhimurium causes diarrhoea, while S. typhi is the causative agent of typhoid fever.

Unlike most bacteria, the Cyanophyta or blue-greens undertake photosynthesis. Their photosynthetic pigments include chlorophyll a but none of the other forms of chlorophyll found in plants. The chlorophyll is bound to infoldings of the cell membrane. Many blue-green algae exist as groups of cells arranged as long filaments. Some are capable of nitrogen fixation.

Text © University of Cape Town Zoology Department

Genera

Acetobacter

Acid-producing, nitrogen-fixing bacteria that are associated with plants. They are able to fix atmospheric nitrogen under aerobic (oxygen present) conditions. Acetobacter also plays a role in the fermentation of vinegar from rice (komesu in Japanese).

Acinetobacter

Aerobic, non-fermentative bacteria that occur widely in water, soil and living organisms. They occur naturally on the human skin but can cause disease, especially through open wounds contaminated by soil. This has been a problem in war situations where these types of wounds occur. Acinetobacter species also exist in hospitals where they can be a source of infection for patients with low disease resistance thresholds. In general, Acinetobacter species do not cause disease in healthy individuals but in immunocompromised patients they can cause pneumonia, meningitis, bacteremia (bacteria in the blood), and skin and wound infections.

Aeromonas

Termed a facultative anaerobe, because it can exist in the presence of oxygen and use oxygen  for aerobic respiration, but it can also exist in anaerobic (non-oxygenated) conditions where it derives its energy from fermentation of organic substances such as carbohydrates. Found abundantly in fresh and brackish water, as well as in food. Can cause disease in humans in that it is one of the bacteria that can cause gastroenteritis (inflammation of the gut) with accompanying diarrhea, and wound infections. Can also cause disease in fish and frogs that are exposed to stressful conditions. About 14 species have been described.

Agrobacterium

 

Alcaligenes

 

Alcanivorax

 

Anabaena

 

Aquifex

 

Arthrobacter

 

Azoarcus

 

Azotobacter

 

Bacillus

 

Bacteroides

 

Bartonella

 

Bdellovibrio

 

Beggiatoa

 

Bifidobacterium

 

Bordetella

 

Borrelia

 

Bradyrhizobium

 

Brucella

 

Burkholderia

 

Campylobacter

 

Candidatus

 

Chloracidobacterium

 

Caulobacter

 

Chlamydia

 

Chlorobium

 

Chloroflexus

 

Chroococcus

 

Clostridium

 

Corynebacterium

 

Coxiella

 

Dehalobacter

 

Deinococcus

 

Desulfosarcina

 

Desulfovibrio

 

Desulfuromonas

 

Enterobacter

 

Enterococcus

 

Epulopiscium

 

Erysipelothrix

 

Erythrobacter

 

Erythromicrobium

 

Escherichia

 

Flavobacterium

 

Flexibacter

 

Frankia

 

Fusobacterium

 

Gallionella

 

Gemmata

 

Geobacter

 

Halomonas

 

Helicobacter

 

Klebsiella

 

Lactobacillus

 

Legionella

 

Leptospira

 

Leptospirillum

 

Leptothrix

 

Listeria

 

Marinobacter

 

Magnetotactic

 

Merismopedia

 

Methylobacterium

 

Micrococcus

 

Mitochondria

 

Mycobacterium

There are numerous species of Mycobacterium and some species are found just about everywhere, such as in water (including drinking water and swimming pools) and soil. Some are beneficial such as Mycobacterium austroafricanum, which breaks down a toxic petroleum additive. However, there are many that do cause disease in both animals and humans. The most important human disease species are Mycobacterium tuberculosis (the main causitive agent of tuberculosis), Mycobacterium leprae (causes leprosy) and Mycobacterium ulcerans (causes Buruli ulcer). There are a number of species found in water and soil that cause Nontuberculous Mycobacteria (NTM) lung disease, mainly a problem with immunosupressed individuals such as people infected with HIV.

Mycoplasma

 

Myxococcus

 

Neisseria

 

Nitrosococcus

 

Nitrosomonas

 

Nitrospira

 

Nostoc

 

Pasteurella

 

Petrotoga

 

Pirellula

 

Planctomyces

 

Pleurocapsa

 

Porphyromonas

 

Prevotella

 

Prochlorococcus

 

Prochloron

 

Propionibacterium

 

Prosthecobacter

 

Prosthecomicrobium

 

Proteobacteria

 

Providencia

 

Pseudomonas

 

Psychrobacter

 

Rhizobium

 

Rhodobacter

 

Rhodopseudomonas

 

Rhodospirillum

 

Rickettsia

 

Roseobacter

 

Ruminobacter

 

Ruminococcus

 

Salmonella

 

Shigella

 

Sinorhizobium

 

Sphaerotilus

 

Sphingomonas

 

Spirillum

 

Spirulina

 

Staphylococcus

 

Streptococcus

 

Streptomyces

 

Succinomonas

 

Succinivibrio

 

Synechococcus

 

Thermodesulfobacterium

 

Thermotoga

 

Thermus

 

Thiobacillus

 

Thiocapsa

 

Thiomargarita

 

Treponema

 

Trichodesmium

 

Verrucomicrobium

 

Vibrio

 

Wigglesworthia

 

Wolbachia

 

Xanthomonas

 

Yersinia

 

 


Contact us if you can contribute information or images to improve this page.

Biodiversity Explorer home   Iziko home   Search