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Topic Review
Sulfate-Reducing Microorganisms
Sulfate-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. Most sulfate-reducing microorganisms can also reduce some other oxidized inorganic sulfur compounds, such as sulfite (SO32–), dithionite (S2O42–), thiosulfate (S2O32–), trithionate (S3O62–), tetrathionate (S4O62−), elemental sulfur (S8), and polysulfides (Sn2−). Depending on the context, "sulfate-reducing microorganisms" can be used in a broader sense (including all species that can reduce any of these sulfur compounds) or in a narrower sense (including only species that reduce sulfate, and excluding strict thiosulfate and sulfur reducers, for example). Sulfate-reducing microorganisms can be traced back to 3.5 billion years ago and are considered to be among the oldest forms of microbes, having contributed to the sulfur cycle soon after life emerged on Earth. Many organisms reduce small amounts of sulfates in order to synthesize sulfur-containing cell components; this is known as assimilatory sulfate reduction. By contrast, the sulfate-reducing microorganisms considered here reduce sulfate in large amounts to obtain energy and expel the resulting sulfide as waste; this is known as dissimilatory sulfate reduction. They use sulfate as the terminal electron acceptor of their electron transport chain. Most of them are anaerobes; however, there are examples of sulfate-reducing microorganisms that are tolerant of oxygen, and some of them can even perform aerobic respiration. No growth is observed when oxygen is used as the electron acceptor. In addition, there are sulfate-reducing microorganisms that can also reduce other electron acceptors, such as fumarate, nitrate (NO3−), nitrite (NO2−), ferric iron [Fe(III)], and dimethyl sulfoxide. In terms of electron donor, this group contains both organotrophs and lithotrophs. The organotrophs oxidize organic compounds, such as carbohydrates, organic acids (e.g., formate, lactate, acetate, propionate, and butyrate), alcohols (methanol and ethanol), aliphatic hydrocarbons (including methane), and aromatic hydrocarbons (benzene, toluene, ethylbenzene, and xylene). The lithotrophs oxidize molecular hydrogen (H2), for which they compete with methanogens and acetogens in anaerobic conditions. Some sulfate-reducing microorganisms can directly utilize metallic iron [Fe(0)] as electron donor, oxidizing it to ferrous iron [Fe(II)].
  • 1.1K
  • 04 Nov 2022
Topic Review
Sand Dam Technology
Sand dam technology filters and protects water from contamination and evaporation with low to no maintenance cost. Sand dams improve the socio-economy of the community and help to cope with drought and climate change. However, success depends on the site selection, design, and construction. The ideal site for a sand dam is at a transition between mountains and plains, with no bend, intermediate slope, and impermeable riverbed in a catchment with a slope greater than 2°. The spillway dimensioning considers the flow velocity, sediment properties, and storage target, and the construction is in multi-stages. Recently, the failure of several sand dams because of incorrect siting, evaporation loss, and one-stage construction were reported. Revision of practitioners’ manuals by considering catchment scale hydrological and hydrogeological characteristics, spillway height, and sediment transport are recommended. Research shows that protected wells have better water quality than open wells and scoop holes. Therefore, the community should avoid open defecation, pit latrines, tethering of animals, and applying pesticides near the sand dam. 
  • 1.1K
  • 01 Jul 2021
Topic Review
Climate Change and Ecosystems
Climate change has adversely affected both terrestrial and marine ecosystems, and is expected to further affect many ecosystems, including tundra, mangroves, coral reefs, and caves. Increasing global temperature, more frequent occurrence of extreme weather, and rising sea level are among some of the effects of climate change that will have the most significant impact. Some of the possible consequences of these effects include species decline and extinction, behavior change within ecosystems, increased prevalence of invasive species, a shift from forests being carbon sinks to carbon sources, ocean acidification, disruption of the water cycle, and increased occurrence of natural disasters, among others.
  • 1.1K
  • 04 Nov 2022
Topic Review
Polycyclic Aromatic Hydrocarbons
Polycyclic aromatic hydrocarbons (PAHs) is an organic pollutant with persistence and carcinogenicity. They are universally present in the environment and food processing. Biological approaches toward remediating PAHs-contaminated sites are a viable, economical, and environmentally friendly alternative compared to conventional physical and/or chemical remediation methods. Recently, various strategies relating to low molecular weight organic acids (LMWOAs) have been developed to enhance the microbial degradation of PAHs. However, the remaining challenge is to reveal the role of LMWOAs in the PAHs biodegradation process, and the latter limits researchers from expanding the application scope of biodegradation.
  • 1.1K
  • 24 Feb 2021
Topic Review
Toward a Feminist Agroecology
Agroecology is gaining ground as a movement, science, and set of practices designed to advance a food systems transformation which subverts the patterns of farmer exploitation currently entrenched in dominant agricultural models. A feminist agroecology focuses on redressing unequal gender relations as well as other intersecting relations of marginalization such as race, class, caste, and ethnic identity. 
  • 1.1K
  • 20 Oct 2021
Topic Review
Wetlands in China
China has a wetland area of 53.42 million hectares, the fourth largest in the world; it includes all types of wetlands defined by the Ramsar Convention and has a carbon sink capacity of more than 1.71 million metric tons per year. Inland wetlands in China are mainly distributed in 10 major catchments, among which the Yellow River, the Yangtze River, the rivers in the northwest, and the rivers in the northeast each have more than 8 million hectares of wetlands. There are 4220 species of plants and 4015 species of animals in China’s wetland ecosystem. The wetland resources that have been developed and utilized include edible products, reeds for paper making, peat for fertilizer, fuel for power generation, and chemical, pharmaceutical, ceramic, and building materials. Wetland areas in China have shrunk by about 54% since 1980.
  • 1.1K
  • 18 Jul 2022
Topic Review
Scientific Opinion on Climate Change
Scientific opinion on climate change is a judgment of scientists regarding the degree to which global warming is occurring, its likely causes, and its probable consequences. A related—but not identical—term, "scientific consensus on climate change," is the prevailing view on climate change within the scientific community. The consensus is that:
  • 1.1K
  • 29 Nov 2022
Topic Review
The NifA–NifL System for Nitrogen Fixation
Nitrogen–fixing bacteria execute biological nitrogen fixation through nitrogenase, converting inert dinitrogen (N2) in the atmosphere into bioavailable nitrogen. Elaborating the molecular mechanisms of orderly and efficient biological nitrogen fixation and applying them to agricultural production can alleviate the “nitrogen problem”. Azotobacter vinelandii is a well–established model bacterium for studying nitrogen fixation, utilizing nitrogenase encoded by the nif gene cluster to fix nitrogen. In Azotobacter vinelandii, the NifA–NifL system fine–tunes the nif gene cluster transcription by sensing the redox signals and energy status, then modulating nitrogen fixation. 
  • 1.1K
  • 06 Feb 2023
Topic Review
Global Storm Activity of 2009
Global storm activity of 2009 profiles the major worldwide storms, including blizzards, ice storms, and other winter events, from January 1, 2009 to December 31, 2009. Wintery storms are events in which the dominant varieties of precipitation are forms that only occur at cold temperatures, such as snow or sleet, or a rainstorm where ground temperatures are cold enough to allow ice to form (i.e. freezing rain). It may be marked by strong wind, thunder and lightning (a thunderstorm), heavy precipitation, such as ice (ice storm), or wind transporting some substance through the atmosphere (as in a dust storm, snowstorm, hailstorm, etc.). Summer storms including flooding, severe thunderstorms and extratropical cyclones (which can occur in summer or winter) are also included in this list to a certain extent. As this occurred a heat wave and/or unforeseen monsoon weather also hit parts of Australia in 2009 and 2010. Victoria, the scene of horrific bushfires the year before, had a far colder summer, with hot weather arriving more than a month later than usual in 2009. August 17 saw a dust storm at Laguna Mar Chiquita as a major drought hit Argentina , and flooding and hailstorms hit southeastern Australia and Queensland in March 2010. The lack of winter precipitation in parts of China, however, contributed to a severe drought in the southwest. Bolivia, Venezuela, Mali, Mauritania, Morocco and Spain have also seen periods of drought in 2009 and 2010. On between May 12 and 26, both Mauritania, the Sénégal River Area and neighbouring parts of both Senegal and Mali faced both a drought and famine in 2010. A storm (from Proto-Germanic *sturmaz "noise, tumult") is any disturbed state of an astronomical body's atmosphere, especially affecting its surface, and strongly implying severe weather. Storms are created when a centre of low pressure develops, with a system of high pressure surrounding it. This combination of opposing forces can create winds and result in the formation of storm clouds, such as the cumulonimbus. Small, localized areas of low pressure can form from hot air rising off hot ground, resulting in smaller meteorological disturbances such as dust devils and whirlwinds.
  • 1.1K
  • 09 Nov 2022
Topic Review
Immobilized Algae Bioremediation Technology
A green technology that immobilizes algae through a carrier to improve biosorbent’s stability and adsorption performance is immobilization technology. An environmentally friendly technology is bioremediation, which uses the metabolic potential of microorganisms to remove heavy metals through a series of physicochemical interactions which occur between the functional groups of microorganisms and the heavy metals.
  • 1.1K
  • 27 Mar 2023
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