The Domain Bacteria

1. The Domain Bacteria

3. Kingdom I: the proteobacteria. This is the largest and most diverse group. It has 5 clusters of species, a, b, g, d e. Key genera Chromatium, Ectothiorhodospira, Rhodobacter, Rhodospirillum.

5. The major genera of proteobacteria. The major groups are Purple phototrophic bacteria Nitrifying bacteria Sulphur and iron oxidisers Hydrogen oxidisers Methanotrophs and methylotrophs Pseudomonas and Pseudomonads Acetic acid Free living aerobic N fixers Neisseria, Chromobacterium Enteric Vibrio and Photobacterium Rickettsias Spirilla Sheathed proteobacteria Budding and Prosthecate Gliding myxobacteria Sulphate and sulpur reducing proteobacteria

6. The Purple phototrophic bacteria carry out anoxygenic photosynthesis and are highly pigmented with bacteriochlorophyll’s and carotenoids.

7. They are split up into sulphur and non-sulphur purple bacteria. They grow photoheterotrophically, needing an organic carbon source. They grow in the anoxic layers in lakes and ponds, below cyanobacteria.

8. Nitifying bacteria These are chemolithotrophs, the key genera are nitrosomas and nitrobacter which are chemolithotrophs that oxidise ammonia to nitrate. They are widespread in soils, in particular where there is a lot of ammonia or protein decomposition eg sewage plants and water receiving sewage. Sulphur and iron oxidisers Thiobacillus and beggiatoa. These are two chemolithotrophs that oxidise sulphur and iron compounds.

9. Beggiatoa filaments in a stream Thiothrix growing in a mineral rich spring

10. Methanotrophs (can grow on methane solely), methylotrophs. These are aerobic bacteria that oxidise methane and other C1 compounds as both electron donors and as the sole carbon source. Widespread in aquatic and terrestrial environments wherever stable methane is present. Methane is produced for example in the anoxic sediments of lakes. Also found symbiotically associated with mussels around hydrothermal vents. Pseudomonas, Pseudomonads. Straight or slightly curved chemoorganotrophic or aerobic rods. Some of these species can grow on a wide range of compounds. Some are important environmentally in water and soil.

13. Free living aerobic N fixers. Azotobacter and Azomonas. These primarily inhabit soils and can be important Nitrogen fixers.

14. Enteric (Intestinal )Bacteria. These include Escherichia, Salmonella, Proteus and Enterobacter. . Among these are many strains pathogenic to humans animals and plants as well as industrial sources. E. coli is the most studied bacterial species. They can be broadly divided into two classes based on their (anaerobic) products, mixed-acid fermentation and 2,3 butanediol fermentation.

16. Escherichia genus are almost exclusively inhabitants of the GI tract of warm blooded animals. Many play a role is synthesising vits, eg. vit K and also using up oxygen thus keeping tract anoxic (facultative). Some strains can cause things like diarrhoea and food poisoning H157. Salmonella have ~ 50% seq. homology. They are almost always pathogenic. Shigellas have 70-100% homology with Escherichia’s and can cause fairly severe forms of gastroenteritis.

17. Sulphate and sulphur reducing proteobacteria. Desulfovibrio, Desulfobacter. Sulphate and sulphur can serve as electron acceptors in anoxic conditions, utilising H2 or organic compounds as e donors. H2S is the product. 20 genera are known. They are widespread in aquatic and terrestrial environments.

18. Kingdom II Gram positives. These are divided into two groups. Low GC and high GC.

19. The non sporulating Low GC G+. Staphylococcus, Micrococcus (This one is high GC, but shares morphology), Streptococcus, Lactobacillus. Staphylococcus and Micrococcus. Both aerobic and catalase positive. Staph are common human and animal parasites. And sometimes cause serious infection. S. epidermidis and S. aureus associated with boils and pimples etc.

20. Lactic acid bacteria. Those below. G+ rods and cocci that produce lactic acid as main/sole fermentation product. They grow anaerobically and are mostly aerotolerant anaerobes. Mostly get energy from sugars. Streptococcus and other cocci. Wide varieties of homofermentitive species. Some are pathogens, fermentors of buttermilk and silage and tooth decay. Lactobacillus are mostly homofermentitive rods. Used to make yoghurt, buttermilk, fermented foods like sauerkraut, silage. They are rarely pathogenic.

21. Endospore forming Low GC G+ Bacillus, Clostridium, heliobacterium. They are mostly saprophytic soil organisms, forming resistant spores helps them survive. Those that cause infections do so opportunistically. Bacillus grows well on defined media. Many produce antibiotics (coupled to sporulation). Some species are thermophilic and some infect insect larvae (B. thu toxin). Clostridium. Lack a cytochrome system and a mech for e transport phosphorylation. Obtain ATP by substrate level phosphorylation only. They are anerobic fermenters the smell of putrefaction is due to them. They live in anoxic pockets in soil. C. botulism and C. tetani and gas gangrene C. perfringens. In these cases producing toxins. Heliobacter are anoxic phototrophs. They fix N in some paddy fields.

22. Cell wall less Low GC: The mycoplasmas. The cells are small and because they don’t have a cell wall, different morphologies can be exhibited in a pure culture. Genome can be as small as 580kb. A lot of pathogens. Hi GC Mycobacterium. Cause TB

23. Filamentous Hi GC G+ the actinomycetes. Large group of filamentous bacteria forming a network of filaments, similar to those formed by fungi. Streptomyces and actinomyces. Many can form spores. Mostly soil organisms, easy to isolate and metabolically versatile, producing hydrolytic enzymes. Known for making antibiotics.

24. Kingdom III. Cyanobacteria, prochlorophytes. Both very closely related. Prochlorophytes don’t have phycobilisomes. They perform oxygenic photosynthesis like plants and alga and are thought to be the forerunners of chloroplasts. They are thought to be responsible for transforming the earths early anoxic to oxic atmosphere. Many different morphological forms and some can differentiate. Some can fix N. As a whole they are very ecologically important.

25. Kingdom IV. Chlamydia. Obligate parasites. Some cause various sorts of pneumonia and trachoma. And STD’s. Very simple metabolically. Kingdom VII Green Sulphur bacteria. Chlorobium. Non motile anoxygenic phototrophs. Unique light harvesting structure called the chlorosome. (also found in green non-sulpur chloroflexus Kingdom X). Found in the depths of lakes and ponds below the purples. Kingdom XI, XII and XIII the hyperthermophiles.