Akash Singh, Banaras Hindu University
In soil ecosystems, microorganisms play an important role in controlling organic matter breakdown and nutrient cycling. According to the enzyme latch hypothesis, under saturated water table conditions, the activity of oxidative enzymes (e.g. polyphenols) is suppressed due to a lack of oxygen (O2) as a necessary reactant, resulting in an accumulation of these oxidative enzymes and, as a result, decreased microbial activity. This notion has been debunked by a study team led by Kelly Wrighton, who has published their decoding of polyphenol metabolism in anoxic soil.
Polyphenols:
Polyphenols are a type of plant chemical that has a wide range of health advantages. They are one of the most common forms of secondary metabolites identified in plants, and they can be found in a variety of settings. They get into soil systems via litter decomposition or leaching. More than 8000 polyphenols have been found to date, and they are divided into four categories: flavonoids, phenolic acids, polyphenolic amides, and other polyphenols.
Polyphenols are processed extensively in human tissues or absorbed past the gut barrier, where they are acted on by the gut microbiota.
Enzyme latch hypothesis:
The Enzyme latch hypothesis is used to justify polyphenol metabolism, which is supposed to be an obligatory aerobic metabolism that cannot function in anoxia. Proposed by Freeman in 2001, claims that in undersaturated water table circumstances, the activity of oxidative enzymes (e.g., phenoloxidase) is suppressed due to a shortage of oxygen (O2) as a necessary reactant. These oxidative enzymes are important for carbon cycling because they help break down phenolic chemicals that inhibit hydrolytic enzymes that cycle carbon and nutrients. Low oxygen availability in the soil suppresses oxidative enzyme activity, resulting in an increase in polyphenols, which bind to hydrolytic enzymes and impede function. Polyphenols accumulate in anoxic soil and function as poisons to microbes, inactivating microbial extracellular enzymes or binding with substrates, depriving microorganisms of nutrition and reducing microbial activity, according to the theory.
Debunking Enzyme latch hypothesis:
Polyphenols are “locks” that stabilize soil carbon, according to the enzyme latch hypothesis. In their most recent study, a group of Colorado State University scientists found evidence for polyphenol breakdown in soils under anoxic conditions, backed up by numerous analytical methodologies. They employed condensed tannin (CT), a polyphenol that underwent abiotic changes and was found to contain CT oligomers, monomers, and other biodegradable compounds.
They demonstrated that the anoxic soil microbiome is capable of polyphenol metabolism, including depolymerization of the CT polymer and subsequent monomer breakdown. They even provided a new multi-omics picture of the soil microbiome’s response to a high molecular weight polyphenol in anoxia. Polyphenols in soils are not as microbially inert as previously thought, according to the research team.
Prospects:
This study adds to a growing amount of recent data debunking long-held beliefs about soil microbiomes’ intractable nature due to their chemical and biological heterogeneity. The study shows how modern soil microbiome technologies can be used to uncover the ecological and biochemical pathways that underpin long-held soil biogeochemical theories. Most of all their findings pave the way for these studies by offering a metabolite and enzyme framework for extracting processes from complicated systems.
Also read: A special chloroplast protein to combat environmental stress
Source:
McGivern, B.B., Tfaily, M.M., Borton, M.A. et al. Decrypting bacterial polyphenol metabolism in an anoxic wetland soil. Nat Commun 12, 2466 (2021). https://doi.org/10.1038/s41467-021-22765-1
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About the Author: Akash Singh is a first-year master’s student of Biochemistry at Banaras Hindu University. He plans to pursue a PhD in the future. He aims to research and teach the young minds of the country.
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