There’s More to Rain Than Water
Food for thought in the civilization of sterility
Macroorganisms — You, insects, plants — need microorganisms to thrive. Ed Yong brilliantly showed in I Contain Multitudes that all species we’ve studied transmit from one generation to the next not only their species DNA, but also the DNA from their microbial symbionts. It appears to be a key parameter for a healthy kick-off in life.
Introduction — a note of the importance of microbe-host cooperation
A good example to understand how species rely on their microbial counterparts is the case of aphids (sap-sucking insects) and their microbial host Buchnera. The bacterium infected aphids about 200 million years ago. They were both living in the same ecological niche, subsiding on phloem sap. For this reason, there was redundancy in their digestive enzymes: they both could use the same metabolic pathways.
Since then, the cohabitation has led both organisms to shed genes that the other symbiont possessed. This happens all the time, but when the genes are needed for survival, the mutation leads to death. When the genes are not needed any more, losing them is actually a gain of energy: there is less to replicate from cell to cell, and less to express.
In time, aphids and Buchnera became team players cooperating on the same production line, and now, they can only digest sap into the amino acids they need by collaborating, one bringing half of the enzymes to the cycle, and the other, the second part. Give an antibiotic treatment of aphids to eliminate Buchnera, and the aphids die of hunger.
So, let’s not think lightly of the collaborations in play across the living realm, between the macro-beasts and the micro-beasts.
The tragedy of impoverished ecosystems
One of the most terrible tragedies of our time is the impoverishment of ecosystems. We are living an unprecedented biological crisis, the 6th mass extinction, with roughly a third of all land vertebrates experiencing considerable losses and becoming at risk of extinction.
This is true also at the level of our gut microbiota: compared to the human ancestral state, the hunter-gatherer lifestyle, as represented by the Tanzanian Hadza, we have lost about 30% in microbial diversity. With consequences on our health at multiple levels.
What about plants’ microbiota?
Agriculture has changed too, and now a lot of vegetables are grown “off-ground” or “hydroponically”, in gigantic greenhouses, where they are grown in a substrate, without exposure to real soil, real sun, nor real rain.
Does it matter?
Well, a recent study pointed to the fact that rain doesn’t only deliver water. After observing greater densities of microbes on the leaves of rain-exposed tomato plants compared to those grown in the lab, the researchers led by Marco Mechan-Llontop and Boris Vinatzer wanted to determine if rainwater participated in the establishment of plants’ microbiome.
“Although this is a simple question, it is actually really hard to answer since plants outside are exposed to many bacteria that come from the soil, rain, and the air” — Boris Vinatzer
Vinatzer and his colleagues thus designed an experiment in which they collected rainwater and either concentrated its bacterial components, or sterilized them as a control group, before spraying the plant with this inoculum.
The analyses showed that spraying the plants with the microbial communities increased the abundance of over 100 bacterial taxa, demonstrating that rain is indeed a reservoir for plant microbiota exposure and colonization.
“The more we know about these bacteria, the better we can use them to our advantage to improve plant health,” Vinatzer explains, very much in line with the call for urgent microbial literacy in society.
“The more we know about these bacteria, the better we can use them to our advantage to improve plant health”
This is yet another example that thinking about the importance of microbes, or microbial literacy, is needed at all levels of society to design better practices and enhance our chance of survival as a species of superorganism interacting with other ecosystems, in the present global crisis.
Why do we think of this only now, when some of the very first microorganisms ever observed back in the 17th century were in raindrops?
