Last Updated on February 12, 2021 by Sagar Aryal
Syntrophism or syntrophy is a special kind of interaction between two metabolically different organisms where they interact by short-distance metabolite transfer.
- This type of association enables the organisms involved to carry out a metabolic function that neither of them can perform alone.
- The growth of one organism depends on nutrients, growth factors, and the substrate provided by the other.
- The degree of dependence among different species can vary considerably where one of the organisms depends on the other for nutrient supply while aiding in the removal of metabolic products.
- Syntrophy can be described as a resource-service type mutualism as one of the partners provides a chemical compound to the other in exchange for a reward.
- The definition and concept of syntrophy have been a topic of discussion for a long time. The term is now restricted to indicate interactions where the partners depend on each other to perform the metabolic activity and the dependence cannot be overcome by simply adding a co-substrate or a particular nutrient.
- Syntrophism is often used in microbiology to indicate the symbiotic relationship between different bacterial species.
- Hydrogen transfer between microorganisms is considered the heart of syntrophy as it serves as an efficient carrier in reductive metabolism.
- The transfer of electrons can occur in different ways, either by the transfer of chemical compounds or organic and inorganic mediators.
- Different studies have indicated that microbes involved in syntrophic association often have evolved molecular mechanisms to establish communication leading to efficient metabolic cooperation.
- Syntrophism is more common in anoxic environments which helps study the workings of microbial life at minimum energy gains.
- The association works by converting endergonic reactions into exergonic in order to exploit minimal resources and support the survival and proliferation of the species involved.
- One of the partners keeps the concentration of the intermediate products low via active consumption so that the other can further degrade the substrate.
Examples of Syntrophism
1. Syntrophic degradation of hexoses
- The anaerobic degradation of hexose sugars is an exergonic process, but the process doesn’t yield enough energy to support the growth of the bacteria.
- In order to achieve a sufficient energy level, the hydrogen pressure in the system is to be reduced.
- In anoxic environments with complex microbial communities consisting of methanogens and homoacetogens, these bacteria work together to maintain a low hydrogen pressure while increasing energy per mole of the substrate.
- The increase in energy yield facilitates complete fermentation of hexoses into acetate, CO2, and H2. These end products are then further metabolized by methanogenic and homoacetogenic partners.
- In the absence of such interactions, the fermentation shifts towards the production of butyrate, ethanol, and lactate.
2. Syntrophic degradation of amino acids
- Degradation of proteins yields a mixture of amino acids and smaller peptides which are then subsequently metabolized by anaerobic microbes.
- Under anoxic conditions, degradation of amino acids is obtained by coupling of oxidation and reduction of amino acids to produce carboxylic acids.
- During this process, hydrogen production can occur in the absence of electron acceptors. In a complex microbial community, however, the electrons are removed by transferring it to sulfate-reducing, homoacetogenic or methanogenic bacteria.
- The transfer help maintain the level of hydrogen, thus, facilitating the degradation of further amino acids.
3. Bacteria in the rumen
- Rumen in ruminants consists of a complex group of microorganisms, most of which are syntrophic.
- The anaerobic degradation of organic compounds in the rumen results in the production of fatty acids and hydrogen.
- The accumulation of hydrogen in the rumen then inhibits the ability of the microorganisms to continue the degradation of organic matter.
- However, the microbial community consists of hydrogen-consuming microbes in a syntrophic association in order to allow further degradation.
- The hydrogen-consuming microbes include methanogens, acetogens, and sulfate-reducers.
- Thus, the syntrophic association between the hydrogen-consuming microbes and the fermenters enables continuous degradation of organic compounds and growth of both the partners.
References and Sources
- Schink B., Stams A.J.M. (2013) Syntrophism Among Prokaryotes. In: Rosenberg E., DeLong E.F., Lory S., Stackebrandt E., Thompson F. (eds) The Prokaryotes. Springer, Berlin, Heidelberg. https://doi.org/10.1007/978-3-642-30123-0_59
- Morris BE, Henneberger R, Huber H, Moissl-Eichinger C. Microbial syntrophy: interaction for the common good. FEMS Microbiol Rev. 2013 May;37(3):384-406. doi: 10.1111/1574-6976.12019. PMID: 23480449.
- Kouzuma, Atsushi et al. “Microbial interspecies interactions: recent findings in syntrophic consortia.” Frontiers in microbiology vol. 6 477. 13 May. 2015, doi:10.3389/fmicb.2015.00477.
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