A transformed version of the energy source, such as elemental sulfur or ferric iron. A commonly used example equation for chemosynthesis shows the transformation of carbon dioxide into sugar with the help of hydrogen sulfide gas:. This equation is sometimes reduced to its simplest possible ratio of ingredients. This shows the relative proportions of each ingredient necessary for the reaction, although it does not capture the full quantity of hydrogen sulfide and carbon dioxide necessary to create a single sugar molecule.
Chemosynthesis allows organisms to live without using the energy of sunlight or relying on other organisms for food. Like chemosynthesis, it allows living things to make more of themselves.
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By turning inorganic molecules into organic molecules, the processes of chemosynthesis turn nonliving matter into living matter. Today it is used by microbes living in the deep oceans, where no sunlight penetrates; but it is also used by some organisms living in sunny environments, such as iron bacteria and some soil bacteria. Some scientists believe that chemosynthesis might be used by life forms in sunless extraterrestrial environments, such as in the oceans of Europa or underground environments on Mars. It has been proposed that chemosynthesis might actually have been the first form of metabolism on Earth, with photosynthesis and cellular respiration evolving later as life forms became more complex.
The example equation for chemosynthesis given above shows bacteria using a sulfur compound as an energy source. The bacteria in that equation consumes hydrogen sulfide gas 12H 2 S , and then produces solid, elemental sulfur as a waste product 12S. Some bacteria that use chemosynthesis use elemental sulfur itself, or more complex sulfur compounds as fuel sources, instead of hydrogen sulfide. Iron bacteria can actually pose a problem for water systems in iron-rich environments, because they consume dissolved metal ions in soil and water — and produce insoluble clumps of rust-like ferric iron, which can stain plumbing fixtures and even clog them up.
However, iron bacteria are not the only organisms that use metal ions as an energy source for chemosynthesis. Other types of bacteria use arsenic, manganese, or even uranium as sources of electrons for their electron transport chains! Nitrogen bacteria are any bacteria that use nitrogen compounds in their metabolic process. While all of these bacteria use electrons from nitrogen compounds to create organic compounds, they can have very different effects on their ecosystem depending on what compounds they use. Nitrifying bacteria grow in soils that contain ammonia.
Ammonia is an inorganic nitrogen compound that is toxic to most plants and animals — but nitrifying bacteria can use it for food, and even turn it into a beneficial substance. Nitrifying bacteria takes electrons from ammonia and converts the ammonia into nitrites, and ultimately nitrates. Nitrates are essential for many ecosystems because most plants need them to produce essential amino acids. Nitrification is often a two-step process: one bacteria will convert ammonia into a nitrite, and then another bacteria species will convert that nitrite into a nitrate. Nitrifying bacteria can turn otherwise hostile soils into fertile grounds for plants, and subsequently for animals.
Denitrifying bacteria use nitrate compounds as their source of energy. In the process, they break these compounds down into forms that plants and animals cannot use. This means that denitrifying bacteria can be a very big problem for plants and animals — most plant species need nitrates in the soil in order to produce essential proteins for themselves, and for the animals that eat them.
Denitrifying bacteria compete for these compounds, and can deplete soil, resulting in limited ability for plants to grow. These bacteria are very beneficial to ecosystems, including human agriculture. They can turn nitrogen gas — which makes up most of our atmosphere — into nitrates that plants can use to make essential proteins. Historically, fertility issues and even famine have happened when soil became depleted of nitrates due to natural processes or overuse of farmland.
Many cultures learned to keep soil fertile by rotating nitrogen-consuming crops with nitrogen-fixing crops. The secret of nitrogen-fixing crops is that the plants themselves do not fix nitrogen: instead, they have symbiotic relationships with nitrogen-fixing bacteria. Modern fertilizers are often made of artificial nitrates, like those compounds made by nitrogen fixing bacteria. Both archaeabacteria and true bacteria are single-celled prokaryotes — which means they look pretty similar under the microscope.
But modern methods of genetic and biochemical analysis have revealed that there are important chemical differences between the two, with archaeabacteria using many chemical compounds and possessing many genes not found in the bacteria kingdom. Only archaeabacteria species can combine carbon dioxide and hydrogen to produce methane. Methanobacteria live in a variety of environments — including inside your own body! Methanobacteria are found at the bottom of the ocean, in swamps and wetlands, in the stomachs of cows — and even inside human stomachs, where they break down some sugars we cannot digest in order to produce methane and energy.
Biology Dictionary. Chemosynthesis Definition Chemosynthesis is the conversion of inorganic carbon-containing compounds into organic matter such as sugars and amino acids. Chemosynthesis Equation There are many different ways to achieve chemosynthesis. However, all equations for chemosynthesis typically include: Reactants: A carbon-containing inorganic compound, such as carbon dioxide or methane. An organic compound such as a sugar or amino acid. Answer to Question 1. B is correct. Chemosynthesis does NOT require energy from sunlight.
For this reason it can be used by organisms in lightless ecosystems, such as the bottom of the ocean. Color code indicates which fatty acids were more likely to be indicative of chemoautotrophy red or photoautotrophy green. Incubations in the dark as a function of time 6, 12, 24, or 48 h and sediment depth 0—2, 2—4, 4—6, 6—8, or 8—10 cm were performed to obtain further insights into the chemosynthetic activity at different redox interfaces. This suggests that microbially mediated iron cycling plays an important role in the biogeochemistry of the Dominica shallow hydrothermal system, which would be in accordance with other iron-enriched shallow-water hydrothermal systems off Santorini Greece or Tutum Bay Papua New Guinea Handley et al.
The most well documented marine iron oxidizer is Mariprofundus ferrooxydans belonging to the Zetaproteobacteria Emerson et al. This is in accordance with the cultivation conditions of Mariprofundus , which grows as an oxygen-dependent obligate lithotroph at a pH range of 5. Iron-oxidizing Zetaproteobacteria have previously been found mainly at deep-sea hydrothermal vents Emerson and Moyer, ; Kato et al.
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In addition to iron-oxidizers, we could also identify numerous taxa potentially capable of reducing iron, mainly Deltaproteobacteria. Although Shewanellaceae of the Gammaproteobacteria are among the most commonly identified iron-reducing bacteria Zhang et al. In contrast, the thermophilic genus Geothermobacter , originally isolated from a deep-sea hydrothermal vent Kashefi et al.
Geothermobacter was among the five most abundant genera of the whole dataset, indicating its importance for iron cycling at the studied vent system. We further detected other less abundant iron-reducing taxa that are also known to be able to use sulfur as electron acceptor, like Deferribacteres, Desulfobulbus , and Desulfuromonas. This is in accordance with previous studies of hydrothermal ecosystems, including shallow-water vents Takai et al. Other highly abundant chemolithotrophic genera that obtain energy via oxidation of reduced chemical species other than iron were detected in our study.
In line with these findings, all of these taxa have been previously found at thermally active sites or deep-sea hydrothermal vents e. The autotrophic bacterial community composition of the Dominica shallow-water vents varied with sediment depth, with a clear dominance of a mixed photo- and chemoautotrophic community in the surface layer and exclusively chemoautotrophic microorganisms in the deeper layers. This is consistent with the findings at another iron-enriched shallow-water hydrothermal systems off Santorini Greece Handley et al. To further investigate the process of chemoautotrophic carbon fixation, we combined the DNA-based diversity analysis with SIP of lipid biomarkers, which provides information on the metabolic and physiological state of microbial communities in environmental samples Wegener et al.
Increase of 13 C-incorporation into diagnostic lipids, for instance 10Me- C , points to the activity of iron reducers because this fatty acid has previously been reported to be a specific biomarker for deltaproteobacterium Geobacter sp. Lovley, ; Zhang et al. This is consistent with previous literature describing the branched fatty acids i C and ai C as deriving from sulfate reducing bacteria SRB; Hinrichs et al.
Our bacterial analysis would be consistent with the possibility of linking these fatty acids to microbial sulfur cycling e. In marine shallow-water hydrothermal systems, chemosynthesis could be enhanced by the increased availability of oxygen as an electron acceptor due to its production by diatoms or cyanobacteria during oxygenic photosynthesis.
Nonetheless, our fatty acid results did not support the possibility of active diatoms in the system, as we did not detect long-chain polyunsaturated fatty acids known to be produced by diatoms Volkman et al. In contrast, the high relative abundance of sequences belonging to the phylum Chloroflexi detected in our study suggests that they could play an important role in the Dominica shallow-water hydrothermal system.
Chloroflexi function either as heterotrophs or as anoxygenic photoautotrophs.
Reports about the fatty acid inventory of Chloroflexi vary in the literature with either ai C , ai C , i C , and C Yamada et al. Interestingly, we classified the former set of fatty acids known to be present in thermo- and mesophilic Chloroflexi Yamada et al. We argue that Chloroflexi are unlikely to perform anoxygenic photoautotrophy in the Dominica system, and that most of the fatty acids with high 13 C-bicarbonate incorporation i.
Accordingly, the Chloroflexi classes identified in our study, i. This would be consistent with the high relative abundance of Anaerolinea thermophila in surface and subsurface layers of the iron-rich Santorini shallow-water hydrothermal system, where Chloroflexi were also proposed to be heterotrophs, and not contributing to primary production Handley et al. However, our incubations were performed for a maximum of 48 h and previous studies have shown that incubation times shorter than one to 2 weeks seem to prevent labeling of heterotrophic organisms due to cross-feeding Knief et al.
Therefore, our experiments are likely to have primarily targeted autotrophic microorganisms, but co-assimilation of CO 2 by autotrophs and active members of the heterotrophic community, including thermo- or mesophilic Chloroflexi , cannot be fully excluded e. However, recent studies concluded that dark carbon fixation by chemoautotrophic bacteria can be a major process in the carbon cycle of coastal sediments Middelburg, ; Boschker et al.
At marine shallow-water hydrothermal systems, chemosynthesis driven by the availability of reduced chemicals is a process that co-occurs with photosynthesis Tarasov et al. However, longer incubations lead to slower incorporation rates, especially in the deeper layers, most likely due to the limited supply of both reduced substrates, e.
This is supported by the observation that chemosynthesis was initially present at similar depths in our study as in another study focusing on intertidal permeable sediments e. In contrast, in sulfidic marine coastal sediments from the North Sea dominated by diffusion, chemoautotrophy was restricted to the oxygenated top 0. This supports the critical role of hydrothermal circulation in the permeable sediments of the Dominica shallow-water hydrothermal system in driving chemosynthesis in deeper sediment layers.
Given the relevance of chemosynthesis in the carbon cycle e. To our knowledge, very few studies have quantified rates of chemoautotrophic production in marine coastal environments or brackish lake sediments not influenced by hydrothermal activity Enoksson and Samuelsson, ; Thomsen and Kristensen, ; Lenk et al. Therefore, global estimates of chemoautotrophy are currently limited e. In the present study, we combined SIP of lipid biomarkers with DNA-based bacterial community structure analysis to investigate the relative importance of chemoautotrophy in a light-exposed, iron-enriched marine shallow-water hydrothermal system off Dominica Lesser Antilles.
Relatively elevated 13 C-incorporation under dark conditions allowed classification of branched and odd-chain fatty acids ai C , C and i C as potential lipid biomarkers for chemoautotrophic bacteria in the Dominica system.
Furthermore, our study identified the Dominica marine shallow-water hydrothermal system as a hotspot for microbes involved in iron cycling e. GG-S and SB designed the research. GG-S analyzed data and wrote the manuscript with help and input from all co-authors. The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.
Amend, C. Kleint, A. Koschinsky, T. Pichler, M. Sollich and S. Thanks to the Dominican Department of Fisheries, especially to A. Magloire for granting sample permission, O. Lugay for providing logistical support and A. Madisetti for joining the sampling with underwater photography. Special thanks to B. Dieterich, X. Prieto-Mollar, and J. Wendt for laboratory assistance and to L.
Schubotz for valuable advices. Friedrich for providing facilities to perform molecular laboratory work. We also thank the two reviewers whose comments helped to improve an earlier version of this manuscript. National Center for Biotechnology Information , U. Journal List Front Microbiol v. Front Microbiol. Published online Apr Gonzalo V.
Stefan M. Solveig I. Author information Article notes Copyright and License information Disclaimer. Reviewed by: Sean M. Gomez-Saez, ed. This article was submitted to Microbiological Chemistry and Geomicrobiology, a section of the journal Frontiers in Microbiology. Received Jan 30; Accepted Apr 5. The use, distribution or reproduction in other forums is permitted, provided the original author s or licensor are credited and that the original publication in this journal is cited, in accordance with accepted academic practice.
No use, distribution or reproduction is permitted which does not comply with these terms. This article has been cited by other articles in PMC. Abstract The unique geochemistry of marine shallow-water hydrothermal systems promotes the establishment of diverse microbial communities with a range of metabolic pathways. Keywords: chemoautotrophy, marine shallow-water hydrothermal systems, lipid biomarker, stable isotope probing SIP , fatty acids, Dominica Lesser Antilles , Zetaproteobacteria , Geothermobacter. Open in a separate window.
Bacterial Diversity Analysis The bacterial diversity of the five sediment depth layers 0—2, 2—4, 4—6, 6—8, and 8—10 cm was analyzed from one of the cores incubated in the dark for 48 h, which might bias the results if interpreted as natural community composition. Lipid Biomarkers Analysis Total lipids were extracted from freeze-dried sediment samples following a protocol based on Bligh and Dyer and modified by Sturt et al.
Statistical Analysis A non-metric multidimensional scaling NMDS analysis was performed in order to assess how incubated samples during 6—48 h in the dark were similar or differ from each other based on the incorporation of 13 C-bicarbonate into different fatty acids. Results Bacterial Community Composition Bacterial community analysis of the incubated samples revealed variations in the taxonomical composition as a function of sediment depth. Linking Lipid Signatures to the Microbial Carbon Metabolism To further investigate the process of chemoautotrophic carbon fixation, we combined the DNA-based diversity analysis with SIP of lipid biomarkers, which provides information on the metabolic and physiological state of microbial communities in environmental samples Wegener et al.
Conclusion In the present study, we combined SIP of lipid biomarkers with DNA-based bacterial community structure analysis to investigate the relative importance of chemoautotrophy in a light-exposed, iron-enriched marine shallow-water hydrothermal system off Dominica Lesser Antilles. Conflict of Interest Statement The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.
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