Geometry vs Bacteria and Fungi… Who will win?


Breaking down the microbiology world one bite at a time

Geometry vs Bacteria and Fungi… Who will win?

Soil microbiology is an exciting part of environmental microbiology and science. Researchers in this area mainly study microorganisms that live in the soil, and how they impact plant growth and composition of soil in general. In addition, microbes have vital roles in many biogeochemical cycles, and any disturbances in their ecosystem can accelerate or delay such cycles. Microbial pathways as well as nutrient generation and recycling go hand in hand with plant growth, and scientists are, therefore, eager to study the complex relationships of microbes and plants in the soil. This can be important for the development of new agricultural practices, which will offer a more sustainable and more eco-friendly approach. 

As simple as it sounds, one of the factors that complicate the life of microbes is often an uneven distribution of nutrients in the soil. Microorganisms have to scavenge for them by using quorum sensing and/or utilizing their motility skills (if they have any) until they physically bump into a pool of nutrients. Some researchers hypothesize that certain naturally occurring blockages, like turns, sharp angels, or animate and inanimate objects can prevent the microorganism from accessing simple but highly nutritious molecules. 

To understand how microorganisms overcome those obstacles, Arellano-Caicedo and his colleagues set up an experiment, in which they built an artificial microstructure and inoculated it with the bacterium Pseudomonas putida and the fungus Coprinopsis cinerea. The microstructure had an elaborate shape with many long channels that differed in length, width, and angles of turns. Besides monitoring the progression of growth of these microorganisms, the researchers were also interested in observing interactions that occur between two species in a small, contained structure. Therefore, the experiment consisted of three parts: 1) examining the growth of the bacterium only; 2) examining the growth of the fungus only; 3) examining the growth of the bacterium and the fungus together. What is also interesting about this microstructure is that the channels had different turn angles (45°, 90°, and 109°). This not only created an additional interference for the microorganisms, but also somewhat imitated naturally occurring habitats. 

Types of channels built in the microstructure to observe the growth of the microorganisms (here: C. cinera). Source: article by Arellano-Caicedo et al. 

Clear channels of the microstructure made it easy for the researchers to visualize interactions that took place. At an acute angle of 45°, the first differences in growth appeared. P. putida was more successful in overcoming sharp turns than the fungus. The result can be explained by the fact that this angle is in the natural range of the bacterium’s movement. In a free-swimming environment, bacterial species with innate mechanisms for motility usually move at this angle. For C. cinerea, however, this condition caused problems. As you might know, fungal hyphae like wide spaces, so the angle of 45° drastically constrained the growth. 

Fungi never miss an opportunity to extend their hyphae in all directions! Source:

At wider angles (90° and 109°), both bacterial and fungal growth took an unexpected turn! While the motility and growth of the bacterium was significantly slowed down, the fungus finally got all the space to itself, and started to expand. However, the researchers noticed an interesting phenomenon. When the fungal hyphae hit the walls of the channel, they started to branch out and grow towards both sides. Eventually, one of the sides reached the continuation of the path, while the other grew towards its origin. Such branching resulted in a localized accumulation of biomass in the beginning of the 90° and 109°-angled channels. 

At an angle of 90° and 109°, growing fungal hyphae bumped into the walls of the channel, causing the hyphae to grow in both directions. This event increased fungal biomass at one spot (red circles show the increasing density of the fungal biomass). Source: article by Arellano-Caicedo et al. 

As mentioned earlier, the researchers also wanted to observe interactions that occur between the fungus and the bacterium. When any two organisms grow together, competition for nutrients and space is unavoidable, and this study was not an exception. The results showed that the advancement of fungal hyphae physically changed the environment, causing the bacteria to grow slower. The bacteria were not able to physically push through the fungus, and that stagnated the growth, leading to the depletion of nutrients in places where bacteria accumulated. On the other hand, the fungus had no problem with pushing through bacterial colonies. This observation suggests that bacteria do not alter their spatial habitat in a way that would interfere with fungal growth.

This experiment represents the first step in understanding the dynamics between soil and soil microorganisms. Of course, this research is simplified, and, in real life, many other physical parameters define soil composition than just a turning angle. In nature, soil is often saturated with water or contains gas bubbles that can challenge the movement and growth of bacteria and other microorganisms. In addition, nutrients that microbes encounter in nature are more dispersed and often found in patches. 

Nevertheless, a better understanding of soil microbial ecology can lead to new developments in agriculture. Imagine, for example, a more efficient way of delivering nutrients to a plant root system. By applying the knowledge of soil microbiology and microbial interactions, researchers can develop a more accurate technique of delivering those nutrients, which in the end will benefit microbes and plants. Instead of spending money on extra fertilizers and nutrients, why not develop a way that will be faster and more efficient, based on soil microbiology? Work smarter, not harder! 

Link to the original post: Arellano-Caicedo, C., Ohlsson, P., Bengtsson, M. et al. Habitat geometry in artificial microstructure affects bacterial and fungal growth, interactions, and substrate degradation. Commun Biol 4, 1226 (2021).
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