Темірді тотықтандыратын бактериялар және олардың қызметі

Bacteria deriving energy from dissolved iron

Iron 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. Organic material dissolved in water is often the underlying cause of an iron oxidizing bacteria population. Groundwater may be naturally de oxygenated by decaying vegetation in swamps. Useful mineral deposits of bog iron ore have formed where groundwater has historically emerged and been exposed to atmospheric oxygen. Anthropogenic hazards like landfill leachate, septic drain fields, or leakage of light petroleum fuels like gasoline are other possible sources of organic materials allowing soil microbes to de oxygenate groundwater. A similar reaction may form black deposits of manganese dioxide from dissolved manganese but is less common because of the relative abundance of iron (5.4%) in comparison to manganese (0.1%) in average soils. The sulfurous smell of rot or decay sometimes associated with iron oxidizing bacteria results from the enzymatic conversion of soil sulfates to volatile hydrogen sulfide as an alternative source of oxygen in anaerobic water. Iron is a very important chemical element required by living organisms to carry out numerous metabolic reactions such as the formation of proteins involved in biochemical reactions. Examples of these proteins include iron–sulfur proteins, hemoglobin, and coordination complexes. Iron has a widespread distribution globally and is considered one of the most abundant elements in the Earth's crust, soil, and sediments. Iron is a trace element in marine environments.

Iron oxidizing bacteria colonize the transition zone where de oxygenated water from an anaerobic environment flows into an aerobic environment. Groundwater containing dissolved organic material may be de oxygenated by microorganisms feeding on that dissolved organic material. In aerobic conditions, pH variation plays an important role in driving the oxidation reaction of Fe2+/Fe3+. Therefore, the microbial community has to inhabit microaerophilic regions where the low oxygen concentration allows the cell to oxidize Fe(II) and produce energy to grow. However, under acidic conditions, where ferrous iron is more soluble and stable even in the presence of oxygen, only biological processes are responsible for the oxidation of iron, thus making ferrous iron oxidation the major metabolic strategy in iron rich acidic environments. which are major players in marine ecosystems. Being generally microaerophilic they are adapted to live in transition zones where the oxic and anoxic waters mix. Large, heavily encrusted mats with a gelatinous texture are created by iron oxidizing bacteria as a by product (iron oxyhydroxide precipitation), and can be present around the vent orifices. The vents present at Kamaʻehuakanaloa seamount can be categorized into two types based on concentration and temperature of flow. Those with a focused and high temperature flow (above 50 °C) can be expected to show higher flow rates as well. These vents are characterized by flocculent mats aggregated around the vent orifices. Mat depth at focused, high temperature vents averages in the tens of centimeters, but can vary. In contrast, vents with cooler (10 30 °C) and diffuse flow can create mats up to one meter thick. These mats may cover hundreds of square meters of sea floor.

Iron oxidizing bacteria can pose an issue for the management of water supply wells, as they can produce insoluble ferric oxide, which appears as brown gelatinous slime that will stain plumbing fixtures, and clothing or utensils washed with the water carrying it. The dramatic effects of iron bacteria are seen in surface waters as brown slimy masses on stream bottoms and lakeshores or as an oily sheen upon the water. More serious problems occur when bacteria build up in well systems. Iron bacteria in wells do not cause health problems, but they can reduce well yields by clogging screens and pipes. Treatment techniques that may successfully remove or reduce iron bacteria include physical removal, pasteurization, and chemical treatment. Treatment of heavily infected wells may be difficult, expensive, and only partially successful. Recent application of ultrasonic devices that destroy and prevent the formation of biofilm in wells has been proven to prevent iron bacteria infection and the associated clogging very successfully. Physical removal is typically done as a first step. Small diameter pipes are sometimes cleaned with a wire brush, while larger lines can be scrubbed and flushed clean with a sewer jetter. The pumping equipment in the well must also be removed and cleaned. Iron filters have been used to treat iron bacteria. Iron filters are similar in appearance and size to conventional water softeners but contain beds of media that have mild oxidizing power. As the iron bearing water is passed through the bed, any soluble ferrous iron is converted to the insoluble ferric state and then filtered from the water. Any previously precipitated iron is removed by simple mechanical filtration. Several different filter media may be used in these iron filters, including manganese greensand, Birm, MTM, multi media, sand, and other synthetic materials. In most cases, the higher oxides of manganese produce the desired oxidizing action. Iron filters do have limitations; since the oxidizing action is relatively mild, it will not work well when organic matter, either combined with the iron or completely separate, is present in the water. As a result, the iron bacteria will not be killed. Extremely high iron concentrations may require inconvenient frequent backwashing and/or regeneration. Finally, iron filter media requires high flow rates for proper backwashing, and such water flows are not always available. Wildfires may release iron containing compounds from the soil into small wildland streams and cause a rapid but usually temporary proliferation of iron oxidizing bacteria complete with orange coloration, gelatinous mats, and sulfurous odors. Higher quality personal filters may be used to remove bacteria, odor and restore water clarity.