Microbial Co-Culture Part One: The Concepts

Look up “co-culture” and you will find many meanings, often to do with human culture and groups. But what is Impello talking about when we talk about “co-culturing” microbes? And what does microbial culture have in common with humans?

By Marie Turner, PhD, Creative Director & Head of Science Communications at Impello Biosciences 

For human communities, diverse skills and relationships make our world go round. For example, a company needs people with different abilities such as writers, craftsmen, scientists, and negotiators. A company also needs people with different roles; not everyone can be a boss or have a strong opinion on every topic; there must be a balance. We also might not think of a company as an ecology, but it is: it is a group of living things that interact and thrive (or don’t) in an environment like, say, a brick-and-mortar office or even a virtual space. In any such human group, there might also be trouble makers (people who pick fights, people who hog the snacks, people who never take responsibility). But there are also the peacemakers, the empathetic listeners; the breadwinners and caretakers. However, even more so than any of these individual qualities, what might be most important to a company (or any human team, really,) is how well they know each other and how well they get along. This is why “team-building” is a buzzword in human organizations. What ultimately drives the success or failure of a company is its co-culture, or the way in which individual members interact. 

These concepts make intuitive sense in humans, but what about in other organisms? What about plants? What about microbes?

Microbes work together. 

Anyone who farms in any capacity knows intuitively that, for better or worse, the lives of living things on our croplands or in our greenhouses are inextricably linked. And, we’ve known for a long time that microscopic relationships are critical to plant health and productivity. For example, as early as the 1800s, we recognized that certain organisms like rhizobium were crucial to processes such as the fixation of atmospheric nitrogen, a mechanism by which some plants get their N from the air rather than the soil or synthetic fertilizer. 

However, something we are only recently beginning to understand and put to use is that interactions between and among microbes are just as crucial to overall crop health and productivity as microbe-plant interactions. That is, it is not just what a specific microbial species does, but also what a microbial community does together that ends up mattering for the effectiveness of soil amendments or the crop health of any farm or a growing operation. 

For a long time, the industry has focused on making microbial products look a great deal like our existing agricultural products. For example, microbes that effectively solubilize phosphorus, can be considered good complements or substitutes for organic fertilizers (or non-organic fertilizers), or, if microbes produce insect-killing toxins, like the famous Bacillus thuringiensis (Bt), they can be subbed in for equivalent pesticides. But despite our desire to make individual bacterial species equivalent to individual agricultural chemical inputs, we very quickly discovered that microbes were a far more dynamic and sometimes unknown quantity. That is, we certainly see that organisms like PGPBs (Plant Growth-Promoting Bacteria) have very powerful agricultural effects, but the reasons are often either not clear, or are not easily attributable to one single mechanism. Gradually, we are beginning to understand more of the multiple mechanisms by which individual microbial species create the benefit of biostimulants, biofertilizers, and biopesticides. However, trying to describe what a multispecies biostimulant does by only describing the talents of its individual members, is like trying describe what a human team does by simply presenting a stack of their resumes; it doesn’t really capture anything about what that group of humans is able to accomplish or produce, together. 

So, what is a co-culture and why do microbes make for complicated ingredients? 

As I alluded to earlier, “co-culture” gets defined in a number of ways, but for the purposes of this article, we are going to define a co-culture as two or more microbial types grown together for a particular purpose. Microbial co-cultures are used in a wide variety of technological applications and sectors, from pharmaceuticals, to bioenergy, to environmental remediation. Even things like beer and cheese are microbial co-cultures in which a particular microbial community is used to create a certain flavor profile or texture. In our next article installment about the science of fermentation, we will dive a little more deeply into the science of bioreactors and what makes co-culturing such a challenging (and from our view, necessary) endeavor. For now we’ll just say that microbes can be tricky. So what makes them so? And why do we, at Impello, feel that this scientific challenge is worth contending with, or even must be contended with for the sake of the future of agriculture?

Microbes are social beings.

It might seem kind of strange to think about microbes as social beings, but in fact that is exactly what they are. Obviously, they aren’t social in the exact same way as humans, but what I mean by social is this: microbes “speak” to one another (and to plants), a phenomenon that we have come to call microbial cross-talk (sometimes cross-feeding), and through these communications microbes are able to behave differently when they get together in groups which is a phenomenon we have come to label quorum sensing. So what does this mean in a practical, agricultural sense, what does it have to do with co-culturing, and why, as growers, should we care?

Microbial communications = valuable compounds for plants.

When microbes interact with other microbes in nature, they communicate primarily through the production and release of chemical signals such as lactones, VOCs (volatile organic compounds), and small enzymes, many of which have huge benefits to plant life. Just like there are tens of thousands of words in the English language that human groups can use to shape their conversations, there are also tens of thousands of such molecules that microbes use to talk among themselves and other organisms (like our crop plants!) So, for our purposes here in this blog, it isn’t necessarily important to understand all of these molecules from a biochemical perspective. However, what is important to understand is the kind of messages that these molecular “words” can encode and how they benefit the crop ecosystem around them.

Micro and Macro relationships. 

What are microbes saying to each other? Microbes can make compounds that help them compete with other microbes, which is one reason microbial consortia are effective tools for keeping pathogens at bay without being behaving as biopesticides. But microbes can also have very cooperative relationships. Often, one species or taxonomic group of microbes will produce one biochemical compound that will go on to “collaborate” with other compounds that other microbes make, which means that as a complex multispecies community microbial consortia  are able to produce valuable biochemicals together that they would not be able to on their own. One way to think of these collaborative group communications is as a factory line in which one group of microbes makes a certain part, and then the next microbe makes a different part, and so on and so forth. Just as many multi-talented humans working together are able to build a car or an iPhone, microbial communities, together, are able to make really complex biochemicals! (And, microbes can also work together to break things down. For example, some microbial communities can eat plastic, or take apart and get rid of some nasty, complex molecules as well.) 

In the end, just like a team of humans with diverse talents, microbial communities accomplish far more together than they do alone. It is also important to note that microbial crosstalk does not stop at the microscopic level. Many of the compounds that microbes produce in their “conversations” are the direct result of millions of years of co-evolution with larger macroorganisms (like plants!), meaning that often microbes and plants trade communications back and forth in mutually beneficial ways.  

Bringing nature into the bottle.

The definition of synergy in any system is when a group is more than the sum of its parts. Human teams are so much more than their individuals, and the most inspiring and effective businesses or organizations are always a product of collaboration and synergistic interaction. Likewise, when we expect agricultural microbial products to operate as though they are the same as static agricultural chemicals, we miss out on all of the amazing action and benefit that comes from their dynamic, synergistic relationships. 

In contrast, co-culturing many species of microbes together in a bioreactor gives us back the power of synergy found in natural plant-microbe communities. When we co-culture a community of microbes together in a bioreactor, they must negotiate the space by chemical signaling and in doing so, they re-establish these valuable systems of communication. Also, when we co-culture multiple species together, microbial “crosstalk” and all the plant-beneficial compounds it yields, happens well in advance of when it gets applied to our crops in the field. This means that a co-cultured product, (e.g., continuum) is not only a useful group of individual microbes, but the bottle also contains the “conversation” that it is having among its members. That is, it is a pre-adapted ecosystem in a bottle. By co-culturing, we are able to take advantage of the microbial team getting to know one another (pre-adaptation), and all of the amazing biochemical things they “say” to one another. These biostimulant compounds have a wide range of beneficial effects on plant life, from stimulating growth, to affecting fruit flavor, to boosting natural immunity against bugs and other pathogenic microbes. In future installments, we will dive more deeply into many of these benefits, and also explore some of the science behind microbial team-building (or, as it is more commonly known, co-culture fermentation). 🦠