Eubacteria

Eubacteria (true bacteria)

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