#FEMSmicroBlog: Co-culturing microbes for sustainability


To convert plant biomass into sustainable biofuels, we rely on microbes and their metabolic activities. Many approaches so far focused on cultivating one bacterial strain, while in nature different microbes work together to produce one specific compound. The study “An artificial coculture fermentation system for industrial propanol production” published in FEMS Microbes coupled the synthesis of 2-propanol to the metabolisms of two bacterial species, Propionibacterium freudenreichii and Clostridium beijerinckii. In a #BehindThePaper interview, Michael Sauer explains for the #FEMSmicroBlog, how we could use this synergistic fermentation process in the future.


Can you summarise the significance of your paper for microbiologists outside of your field?

Industrial microbiology is one of the key technologies for fighting climate change. Many problems encountered in our industrial production processes have already been solved by nature and evolution. We just need to open our eyes and understand how nature works to solve our industrial problems.

For example, we can use microorganisms to produce sustainable chemicals which help to keep our standard of living high without an undue use of resources or emission of green-house gases. The special case, presented in our paper, shows that two species of microorganisms working together can achieve remarkable results, which cannot be achieved by one species alone.

Propanol is a useful solvent, which is a natural product of certain microorganisms, but it is usually just a side product, accumulated only in small amounts. We could show here, that by combining two microbial species propanol can become the main product of the process, opening new possibilities for industrial production of this solvent.


What can policymakers learn from your research results?

There are a number of aspects here. I want to start with a philosophic message: Working together is not only more fun than working alone, but the outcome of putting one and one together can be much more than two.

In our study, we started with two microbial species out of which only one produces solvents. We then showed that the overall solvent production of these two species supersedes the possibility of that species alone in the microbial fermentation process.

The non-solvent producer supports the solvent producer in a remarkable way. However, not only the overall amount of solvent increased, but also the product pattern changed. In fact, new products were synthesized by this successful co-working effort. This translates to our macro world quite well, I think.

2-Propanol production from two microbial species. From Hocq et al. (2022).

The second message is that we are just starting to see the real potential of microbial consortia in industrial microbiology. Most of the established processes focus on single species fermentation. However, this is quite an unnatural state for microorganisms.

We show, that combining just two species opens the space of producing new metabolites and we can even think about adding more species. This is a clear indication of how many opportunities have not even been looked at. Much more effort is required to understand microbial communication and co-working with the promise that our own capabilities to use microbes in industry will multiply!


Why are your results important for society or non-scientists?

As I said above: Working together is required. This is not only true for humans but already for organisms in the microbial world. In nature, co-working and antagonism are all around.

Right now, we know hardly anything about how microbial “societies” work. On the one hand, this lack of knowledge is detrimental to our attempts to use microorganisms in industry, because we are not really grasping their true potential.

On the other hand, it is clear that climate change affects not only the visible parts of nature such as plants or animals but also the invisible microbial world. We don’t really know how this world works, so we know even less what climate change might do to it. What we know for sure is that life as we know it entirely depends on the microbial world.

Furthermore, I strongly believe, that industrial microbiology has great potential to reach sustainability. Our study is a nice example for that. Even though it is not an industry-ready process yet, we could show that there is potential to use microbes to produce chemicals sustainably on large scale.


Why did you choose to dive into the topic of this paper? What fascinates you about bacterial co-culture fermentation?

I am fascinated by the world of microbes. I always have been.

Microbiologists study isolated species growing in liquid culture or on solidified liquids like agar. We have gained an incredible amount of knowledge with such studies. However, it more and more turns out that true microbial life in nature is very different from what we studied. A great fraction of all microbes live in much more complex structures. Biofilms for example resemble multicellular organisms in many aspects in which cells have divided tasks to fulfil.

Even in single-species biofilms, cells in different places have different roles with different metabolisms etc. However, unlike higher organisms in which all cells are genetically identical, microbial structures in nature comprise multiple species. Some cells are genetically different while genetically identical cells can also fulfil different functions.

The level of complexity seems therefore unlimited. Trying to understand how two species work together in liquid culture in our study was a first step in understanding that complexity. This simple step already led to remarkable and unexpected results. The prospect of so many more possibilities really excites me!


Why did you choose the transparent peer-review process for your publication?

I see the current system of peer review as problematic in many respects. In an ideal world, a researcher publishes a paper when they have an interesting story to tell and want to share exciting news. Our actual reality is quite different.

Very similar to the microbial world, our behavior is under constant selection. A scientist is expected to publish papers on a regular basis with the number of published papers being decisive for career steps and professional appointments. Yet, most people easily agree that the number of papers published by a person does not really tell a lot about the quality of that person as a scientist.

The decision to submit a publication is therefore not often triggered by a good story, but by the need to publish a paper. Hence, the number of submitted manuscripts is constantly increasing but the quality not necessarily.

This leads to a crisis in our publication system and particularly for peer review, an increasing need for reviewers and increasing conflicts of interest. Our academic lifestyle is more and more characterized by stress and an extreme limit of time, resulting in decreasing quality of the reviews.

Unfortunately, I am not sure how we can solve this issue or IF we can solve it at all without changing our “selection” system in the first place. However, I feel the need to try new ways. I am not sure that the transparent peer-review process is the best solution, but it is an alternative, worthwhile to test and evaluate. So I need to try!


About the author of this blog

Michael Sauer is Associate Professor at the Institute of Microbiology and Microbial Biotechnology of the University of Natural Resources and Life Sciences in Vienna. His research is dedicated to microbial chemical production from renewable resources. The philosophy of his research team is to combine synthetic biology with nature’s diversity and to develop processes as close as possible to industrial realities. One focus is on the characterization and optimization of natural producers, thus exploiting natural diversity. A second line of research is focused on membrane transport processes as metabolic engineering tools.

About this blog section

#BehindThePaper posts on the #FEMSmicroBlog aim to bring the science closer to different audiences and to tell more about the scientific or personal journey to come to the results.

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