Leaf 6
One green leaf
Plant & human microbiomes

☝ Remember Leaf 5 ☘ from last week??

It addressed the #tannins that plants accumulate as precursors for the synthesis of lignin to fortify themselves mechanically.


Besides their utility as astringents and tanning agents, many of these tannins and related phenolics find their way into the soil where they have profound effects that are important for plant growth. 


Although plants can grow using only light for energy, CO₂, water and minerals, most plants depend on micro-organism for getting the minerals from the soil. Particularly important are the nitrogen-fixing bacteria that harvest nitrogen gas (N₂) from the atmosphere, converting it to nitrates needed by plants to make proteins, nucleic acids and other essential biomolecules.  


The soil micro-organisms (the microbiome) live on decaying plant matter and molecules actively secreted by the plant.

It is the nature of these molecules that determines the microbiome profile.  


Different plant species release different assortments of tannins and other molecules to support their own preferred microbiome, encouraging the micro-organism species that support healthy plant growth while deterring lurking opportunistic micro-organisms and pathogens.  


In completely analogous fashion, plant-derived molecules affect the microbiomes of animals and humans. Yes, we too are teaming with bacteria, most of them in the digestive system where they perform important functions in releasing vitamins and nutrients. 


In a healthy gut microbiome, positive bacteria predominate, and part of their activity is to keep harmful bacteria in check. The skin too has an active microbiome, with its bacteria working on dead skin, sweat and sebum secretions, and with beneficial microorganisms competing out harmful ones. 


👉This is where phytochemicals come in. Ingested plant molecules strongly affect the balance between different competing bacteria in the gut. Similarly, application of plant extracts to the skin has selective effects on the skin’s microorganisms. It how the same phytochemical precursors for lignin to fortify plant cells have such far reaching effects, and gives credence to age-old traditions of plant materials to enhance health and appearance. 

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