Chemoautotrophic organisms

Chemoautotrophs organism that obtains its energy from the oxidation of chemical compounds and only uses organic compounds as a source of carbon. 

Photosynthetic organisms plants, algae, bacteria Chemoautotrophic organisms nitrifying bacteria, some sulfur oxidizers, iron oxidizers, hydrogen oxidizers... 

In addition to the pigmented bacteria, some colorless bacteria are able to fix carbon dioxide in the absence of light. These colorless bacteria, known as chemosynthetic or chemoautotrophic organisms, obtain energy for assimilating and reducing CO2 by oxidizing NH3, H2S, and H2. 

Chemoautotrophic organisms, such as bacteria or Archea living in the dark and in hostile environments such as the deep sea, which obtain their energy through the oxidation of inorganics such as H2S, elemental sulfur, metal ions (Fe Mn ", ammonia, or nitrite ... 

Many organic reactions are slow at low temperatures but are considerably accelerated by temperature increases (I). In addition, living organisms themselves, such as chemoautotrophic bacteria, may accelerate reactions involving dead organic matter. 

Thiobacillus ferrooxidans is an obligate chemoautotrophic and acidophilic organism and is able to oxidize Fe2+, S°, metal sulfides, and other reduced inorganic sulfur compounds. Thiobacillus thiooxidans has also been isolated from acid mine wastes and has been determined that can oxidize both elemental sulfur and sulfide to sulfuric acid (S° + 1.502 + H20 - H2S04 and S2 + 202 + 2H+ - H2S04) (Brierley, 1982 Lundgren and Silver, 1980). However, T. thiooxidans cannot oxidize Fe2+ (Harrison, 1984). 

The chemoautotrophic fixation of C02 connected with this activity, only minimally contributes to the carbon cycling in most ecosystems. Notable exceptions to this include the deep-sea hydrothermal vent ecosystems, where the whole vent community is supported by the chemoautotrophic oxidation of reduced sulfur, primarily by Beggiatoa, Thiomi-cropira, and other sulfur oxidizers. In environments other than these, the generation of reduced minerals used in chemolithotrophic production is directly tied to the oxidation of photosynthetically produced organic matter. Therefore, sustainable primary production without solar energy input is unthinkable even in the case of chemolithotrophs. 

FIGURE 72.2. Arsenic detoxification mechanisms (reduction, oxidation, methylation, and resistance) in prokaryotes. (A) Respiratory arsenate reductase (Arr) is involved in the reduction of As(V) by the dissimilatory arsenate respiring organisms. (B) Arsenite oxidase (Aox/Aso) is responsible for oxidation of As(III) by chemoautotrophic or heterotrophic arsenite oxidizers. 

When we subtract the costs of all other metabolic processes by the chemoautotrophs and photoautotrophs, the organic carbon that remains is available for the growth and metabolic costs of heterotrophs. This remaining carbon is called net primary production (NPP) (Lindeman, 1942). From biogeochemical and ecological perspectives, NPP provides an upper bound for all other metabolic demands in an ecosystem. If NPP is greater than all respiratory consumption of the ecosystem, the ecosystem is said to be net autotrophic. Conversely, if NPP is less than all respiratory consumption, the system must either import organic matter from outside its bounds, or it will slowly mn down—it is net heterotrophic. 

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