Microbes are not a luxury item.

Why microbial considerations are every bit as critical as the rest of any growing program.

Written by Marie Turner, Ph.D.

Did you know? So called “germ-free” mice suffer a myriad of physical problems, and then, they die. Young, small, sick, and malformed. 

Maybe you are wondering what on earth a germ-free mouse is, or why am I telling you this in an article about agriculture and horticulture? Let’s start with the first question.

A germ-free mouse is a mouse that is raised in a sterile environment, mice that are deliberately cleansed of all microbes. Extreme care is taken to prevent microbes from ever entering their bodies; all food, water, and bedding are sterilized before the mice get them. This is done in order to study the impact of microbes on host organisms and answer a wide variety of research questions, but one thing is clear: without the diverse microbial communities mice have adapted to over time, they aren’t in good shape. Here are just a few of their problems:

They have underdeveloped immune systems. The lymph nodes, a chief organ in the immune system, are small, and numbers of sickness-fighting cells (like T-cells and B-cells) are reduced.

They have malformed brains and guts and their metabolism is strange. They have anxious, repetitive behaviors. They eat more calories, but gain less weight; they don’t have the microbes that would usually break down and absorb nutrition or synthesize essential vitamins. 

Their hormone pathways are skewed. They have high levels of stress hormones, and they don’t grow and develop to the full extent normal mice do.

They get sick. Alot. In addition to their own underdeveloped immune system, all bodily “niches” in these mice like the gut are empty and thus prime real estate for the explosion of pathogen populations. Normal gut microbiota also produce a myriad of antimicrobial compounds that fight infection. Not so in germ-free mice.

Okay, okay, so why the mice in an article about growing?

Well, in some ways, the ways in which we grow crops in the modern world are a little like rearing germ-free mice in the lab. That is, we often go out of our way, especially in controlled environments, to rid the space of microbes. In field agriculture, of course, we can never do this, but we do use broad spectrum chemicals that eliminate good and bad bacteria, and many of the agronomic practices we are accustomed to (like tillage) destroy microbial habitat. So while fields might not ever be truly “germ-free”, countless studies show conventional fields are definitely “germ-altered” with both reduced numbers and diversity of microbes.

 

Why should we care?  

Well, just like in other host organisms like mice, plants have co-evolved over long periods of time to optimize their performance and health via microbes. We know that microbes:

Modify plant stress and immune systems. Just like in mice, microbes help plants withstand all kinds of biotic and abiotic stress, and improve plant ability to continue to uptake water and nutrients in challenging environments.

Cycle all kinds of nutrients. Just like microbes metabolize food for mice, microbes “feed” organic material to plants by breaking it down into forms the plant can use. They chelate (bind) other unavailable nutrients and make them plant-accessible.

Influence plant hormone pathways. Microbes enable normal development of mice, and likewise, microbes enable prime growth of plant structures like the ever-critical root system. We might not always look under the “hood” in this way, but ask any young-plant grower who deals in rooting about the difference between microbe-inoculated and uninoculated root growth. A lack of microbes equals stunted roots. 

Without microbes, plants get sick. In addition to supporting a plant’s innate immune systems, microbes have the exact same mechanisms in plant bodies that they have in mouse bodies: they produce a wide range of compounds that actively prevent infection and they take up space and resources that would otherwise be vulnerable to pathogen population explosions.

 

All this is to say, whether in mice or crop plants, microbes are not a luxury. They are a long-standing adaptation that all living macro organisms have in order to survive and to thrive. Like mice, in order to be robust, fully developed, at their prime, plants need microbes.