Sulfur-reducing bacteriaSulfur-reducing bacteria are microorganisms able to reduce elemental sulfur (S0) to hydrogen sulfide (H2S). These microbes use inorganic sulfur compounds as electron acceptors to sustain several activities such as respiration, conserving energy and growth, in absence of oxygen. The final product of these processes, sulfide, has a considerable influence on the chemistry of the environment and, in addition, is used as electron donor for a large variety of microbial metabolisms.
BacteriaBacteria (bækˈtɪəriə; : bacterium) are ubiquitous, mostly free-living organisms often consisting of one biological cell. They constitute a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria were among the first life forms to appear on Earth, and are present in most of its habitats. Bacteria inhabit soil, water, acidic hot springs, radioactive waste, and the deep biosphere of Earth's crust. Bacteria play a vital role in many stages of the nutrient cycle by recycling nutrients and the fixation of nitrogen from the atmosphere.
Groundwater pollutionGroundwater pollution (also called groundwater contamination) occurs when pollutants are released to the ground and make their way into groundwater. This type of water pollution can also occur naturally due to the presence of a minor and unwanted constituent, contaminant, or impurity in the groundwater, in which case it is more likely referred to as contamination rather than pollution.
Purple bacteriaPurple bacteria or purple photosynthetic bacteria are Gram-negative proteobacteria that are phototrophic, capable of producing their own food via photosynthesis. They are pigmented with bacteriochlorophyll a or b, together with various carotenoids, which give them colours ranging between purple, red, brown, and orange. They may be divided into two groups – purple sulfur bacteria (Chromatiales, in part) and purple non-sulfur bacteria.
Sulfate-reducing microorganismSulfate-reducing microorganisms (SRM) or sulfate-reducing prokaryotes (SRP) are a group composed of sulfate-reducing bacteria (SRB) and sulfate-reducing archaea (SRA), both of which can perform anaerobic respiration utilizing sulfate (SO42-) as terminal electron acceptor, reducing it to hydrogen sulfide (H2S). Therefore, these sulfidogenic microorganisms "breathe" sulfate rather than molecular oxygen (O2), which is the terminal electron acceptor reduced to water (H2O) in aerobic respiration.
Iron-oxidizing bacteriaIron-oxidizing bacteria (or iron bacteria) are chemotrophic bacteria that derive energy by oxidizing dissolved iron. They are known to grow and proliferate in waters containing iron concentrations as low as 0.1 mg/L. However, at least 0.3 ppm of dissolved oxygen is needed to carry out the oxidation. When de-oxygenated water reaches a source of oxygen, iron bacteria convert dissolved iron into an insoluble reddish-brown gelatinous slime that discolors stream beds and can stain plumbing fixtures, clothing, or utensils washed with the water carrying it.
Microbial metabolismMicrobial metabolism is the means by which a microbe obtains the energy and nutrients (e.g. carbon) it needs to live and reproduce. Microbes use many different types of metabolic strategies and species can often be differentiated from each other based on metabolic characteristics. The specific metabolic properties of a microbe are the major factors in determining that microbe's ecological niche, and often allow for that microbe to be useful in industrial processes or responsible for biogeochemical cycles.
Bacterial taxonomyBacterial taxonomy is subfield of taxonomy devoted to the classification of bacteria specimens into taxonomic ranks. In the scientific classification established by Carl Linnaeus, each species is assigned to a genus resulting in a two-part name. This name denotes the two lowest levels in a hierarchy of ranks, increasingly larger groupings of species based on common traits. Of these ranks, domains are the most general level of categorization. Presently, scientists classify all life into just three domains, Eukaryotes, Bacteria and Archaea.
Stable isotope ratioThe term stable isotope has a meaning similar to stable nuclide, but is preferably used when speaking of nuclides of a specific element. Hence, the plural form stable isotopes usually refers to isotopes of the same element. The relative abundance of such stable isotopes can be measured experimentally (isotope analysis), yielding an isotope ratio that can be used as a research tool. Theoretically, such stable isotopes could include the radiogenic daughter products of radioactive decay, used in radiometric dating.
Anaerobic respirationAnaerobic respiration is respiration using electron acceptors other than molecular oxygen (O2). Although oxygen is not the final electron acceptor, the process still uses a respiratory electron transport chain. In aerobic organisms undergoing respiration, electrons are shuttled to an electron transport chain, and the final electron acceptor is oxygen. Molecular oxygen is an excellent electron acceptor. Anaerobes instead use less-oxidizing substances such as nitrate (NO3-), fumarate (C4H2O42-), sulfate (SO42-), or elemental sulfur (S).
