Life processes in Bacteria

Bacteria are grouped by how they respire: aerobic bacteria require oxygen as their terminal electron acceptor and cannot grow without it (e.g. Streptococcus), and some, called obligate aerobes (some Micrococcus species), must have oxygen to survive at all; anaerobic bacteria instead obtain energy from fermentation reactions without using oxygen (e.g. Clostridium); facultative anaerobes can switch between the two strategies as conditions demand - E. coli, for instance, can rapidly consume all the available oxygen at an infection site such as an abdominal abscess, creating an anaerobic environment that then lets other anaerobic bacteria present move in and cause further disease (E. coli and Salmonella are classic examples); and capnophilic bacteria (e.g. Campylobacter) specifically require carbon dioxide for growth. They are also grouped by how they feed. Autotrophic bacteria synthesise their own food, and split further into: photoautotrophic bacteria, which use sunlight as their energy source, either as photolithotrophs (using an inorganic hydrogen donor - green sulphur bacteria such as Chlorobium use H2S and the pigment bacterioviridin, while purple sulphur bacteria such as Chromatium use thiosulphate and bacteriochlorophyll) or as photoorganotrophs (using an organic acid or alcohol as hydrogen donor, e.g. the purple non-sulphur bacterium Rhodospirillum); and chemoautotrophic bacteria, which lack photosynthetic pigment and instead draw energy from oxidising organic or inorganic substances, split into chemolithotrophs (oxidising inorganic compounds - sulphur bacteria like Thiobacillus thiooxidans, iron bacteria like Ferrobacillus ferrooxidans, hydrogen bacteria like Hydrogenomonas, and nitrifying bacteria like Nitrosomonas and Nitrobacter) and chemoorganotrophs (oxidising organic compounds - methane bacteria like Methanoc …