The agricultural revolution of 10,000 years ago was thought to be a unique hallmark of Homo sapiens. Now, we know that termites cultivate monocultures of fungi and damselfish farm algae. Humans and animals aren’t the only ones farming – microbes are doing it, too, according to researchers who discovered that a fungus can farm bacteria.

The soil fungus Morchella crassipes, also known as thick-footed morel, is a decomposer as well as a beneficial mycorrhizal fungus that forms symbiotic relationships with plants. The thick-footed morel is also a bacterial farmer. Here are five characteristics of human agriculture that the thick-footed morel also uses to farm the bacteria Pseudomonas putida.

1. Cultivation

In human agriculture, improving a crop’s growth conditions is cultivation. Researchers saw that the thick-footed morel was producing compounds that helped P. putida grow. In fact, P. putida grew significantly more with the help of the thick-footed morel than without it.

2. Harvesting

Researchers found that the fungus was harvesting bacteria when conditions favored resource storage. The fungus are also likely eavesdropping on signals between bacteria to detect how dense the bacteria are growing before harvesting them. To prove the fungus was receiving a benefit from the bacteria, the scientists labeled carbon molecules in glucose and observed the labeled molecules moving from bacteria to fungus. This study is the first to demonstrate carbon transfer from bacteria to fungi.

3. Storage

The thick-footed morel develops structures called sclerotia, which aid in survival by allowing the fungus to store harvested carbon from the bacteria. The fungus can access these nutrient stores when external resources are scarce, much like a grain silo for humans. The researchers washed the storage structures repeatedly and discovered that hundreds of thousands of bacteria are attached to each of the structures. In fact, scientists observed that the thick-footed morel benefited with a reduced stress response.

4. Dispersal

Just as farmers choose certain crops they propagate across their fields, fungi also physically aid in dispersing the bacteria they are cultivating. Fungi have hyphae, which are root-like filaments that extend out in the soil. Bacteria can use these hyphae as “fungal highways”. Most bacteria can’t move efficiently through soil, so bacteria being cultivated by the fungus are able to hitch a ride on the hyphae. This is a huge advantage for the bacteria, who are able to outcompete other species unable to disperse through soil. Scientists even saw that the bacteria were able to cross an air barrier with the help of the fungal highway.

Hyphal highways.Getty

5. Division of labor

Much like division of labor in human societies, parts of the thick-footed morel fungus cultivate the bacteria while other parts help store the carbon for future use. This source-sink system is similar to human agricultural systems, where we move food from the fields to be processed and sold at grocery stores.

These five characteristics were confirmed experimentally using cell counting and 13C isotopic labeling. Much like humans, fungi can use cultivation, harvesting, storage, dispersal, and division of labor to farm bacteria. Don’t fear, hallmarks of agriculture that we can still claim as unique to humans include artificial selection or development as well as cultural transmission of agricultural innovations.

Bacteria and fungi are the main components of the soil microbiome. Soil microbiome research is finishing a rapid discovery phase thanks to relatively cheap next-generation sequencing technology. Now, scientists want to unlock more mechanistic understandings of what is happening between microbes in the soil. This study is an important step in that direction.

Source: Forbes