Let’s start off by clearing a longstanding myth – no, bacteria don’t outnumber human cells by a 10-fold in the body. Scientists have recently found that our bodies contain roughly the same number of bacteria as there are human cells. A vast number of microbes have colonised our bodies, and they’re collectively known as the human microbiota. These microbes affect many aspects of the human health from digestion to mental health and metabolism to immunity. Further research into the human microbiota and their genetic content (the microbiome) will help us understand how our bodies function in conjunction with these beneficial microbes. We can use this information to become healthier and fight diseases.
While the human microbiome has been making headlines recently, most people aren’t even aware that, like humans, plants also host a population of a diverse range of microbes. The plant microbiota includes bacteria, fungi and archaea. Knowledge of the plant microbiome could help us produce more food to feed the growing population, discover new medicines to cure diseases, and even help reverse anthropogenic environmental pollution.
Before we’re able to make these changes, it’s important to understand the function and roles of these microbes both individually and collectively. When scientists find new species, they usually classify them. And scientists have been categorising microbial communities into different classifications based on their evolution and genetic make-up. New initiatives are bringing scholars together from all over the world to build extensive microbial datasets. For example, researchers are collecting microbial samples throughout the world for the Earth Microbiome Project, which will allow us to understand patterns of microbiome distribution relative to their habitat as well as building database.
The problem is that merely classifying microbes doesn’t give us a thorough insight into their function and the roles of their genes. Microbes that live inside plants are also difficult to collect and grow in the lab, so the plant microbiome is an area that remains largely unexplored. Researchers are developing new approaches to collect beneficial microbes in plants. Recent advances in genome sequencing, powerful computational programming and other high-throughput scientific technology are shedding some light on plant microbiome.
Wonders of the plant microbiome
Plant microbiome has many beneficial effects on plant growth and development – the best-known plant-microbe mutualism is the relationship between plants and mycorrhizal fungi (which is technically not a microbe, but hey-ho!). Like the good microbes in the human gut, the mycorrhizal relationship is also hugely beneficial to plants. Here, the fungi associated with the roots supply nutrients, such as nitrogen and phosphorus, to the host plant helping them grow faster. Meanwhile, the plant provides the fungus with sugar. There is also a large population of microbes that reside in plant leaves. Even though the roles of these microorganisms are mostly unknown, some of them show properties that could be good for the plant and the environment.
The plant microbiome could be an untapped source that may help us reduce current air pollution levels.
As well as consisting of a diverse array of microbes, the microbiome varies in different plant species; this is also influenced by the life-stage of plant development and the environment. Plants and the environment share an eternal link. This relationship is critical in the face of the eminent global threat from climate change. Air pollution, mostly generated by rising urban population, is accelerating the rise of average global temperature. It’s contributing to the melting of Antarctic and Arctic ice caps. Cleaner, sustainable energy-source for industry and transportation, and proper city planning can reduce emission. But we also need new ways to get rid of existing air pollution, and quick!
Contaminated air contains many several categories of pollutants that cause significant harm to human health and killing many. The plant microbiome could be an untapped source that may help us reduce current air pollution levels. For example, American grass already contains bacteria that can degrade crude oil but their number increases sharply in grass grown on oily soil. Ivy plants grown in urban areas, with high air pollution, have more bacteria that can break down road traffic-generated particulate matters. Likewise, poplar trees can be hosts to bacteria that can break down organic solvents.
Natural air purifiers
Plants can degrade harmful particles in the air as well break down carbon dioxide through photosynthesis process to produce oxygen. Likewise, several microbes also break down toxic chemicals, including the ones that are present in the atmosphere. We can introduce (inoculate) these microbes into plants to give them an added advantage. The right plant-microbe combo may help us increase food production or clean up the environment.
Recently, scientists inoculated blue pea plants with bacteria that can remove formaldehyde. This volatile organic compound is released as a pollution by-product from industry and is also present in cigarette smoke. Remarkably, the plants colonised by these bacteria grow better in the presence of formaldehyde than plants without bacteria. Although some studies suggest that plants have an innate ability to break down formaldehyde and use them as a carbon source to make sugars, it seems that the bacteria make the plants more efficient in this process. Therefore, plants grown inoculated with these bacteria grow better in the presence of formaldehyde.
Challenges we face to purify contaminated air using plants include identifying plants that already breakdown harmful pollution chemicals, and grow them in the right place. There are (almost) countless numbers of microbes on Earth; many have unique, wacky features that we can, and should exploit to our advantage. Once we identify microbes that break down harmful particles present in air, we can introduce them to plants. Scientists are trying to categorise the most efficient combination of plant and microbe to decontaminate air.
Knowledge of plants and their microbiome content can help us breathe cleaner air both indoors and outdoors. Entire cities may also be planned in the future around plants with the right microbiome. Plants will play a central role in our attempt to curb the effect of climate changes. But we shouldn’t rule out the role plant microbiome may play in this, too.