Several previous posts have extolled the virtues of soil fungi for nutrient transport - especially phosphorous and nitrogen but also carbon and water - as well as their ability to sequester carbon in a durable form: a boon to the soil as well as our atmosphere. They do another neat trick too.

Fungal hyphae play a greater role in the spread of bacteria in the soil than was previously suspected. . . For the first time, scientists have been able to prove that bacteria are able to travel through the soil on the mucous membrane of living fungi. . .

. . . fungi are some of the world’s greatest biomass producers. A single gram of field soil can contain up to 100 metres of mycelium. . .

“For the bacterium a harmful substance is not harmful,” explains Wick. “It simply breaks down the carbon compounds, producing the energy and substances that it needs to live.” But before it can do this it has to get at its ‘food’. Air and lack of moisture present insurmountable obstacles. “This is why certain pollutants are broken down so slowly in the soil. Often it is not a lack of biochemical capacity, but rather a lack of contacts.” The scientists at the UFZ are therefore studying the paths followed by the bacteria.

Mycelia appear to act as a kind of underground highway for bacteria. This is the conclusion reached by Lukas Wick and his team. In the laboratory experiment they succeeded in demonstrating that the bacteria move through the soil on the mycelium. The ingredients: one pollutant, separating layers made of glass pellets, uncontaminated soil and a bacterium called Pseudomonas putida. The bacteria have to fight their way through all these layers to reach the phenanthrene, their ‘food’. This polycyclic aromatic hydrocarbon is a widespread pollutant produced during every combustion process: at petrol stations, in car exhausts, during forest fires, in cigarette smoke and in old municipal gas works.

“We deliberately make the bacteria work their way upwards against gravity so that people can’t say there could be a small amount of water trickling down and carrying the bacteria with it,” says Wick. “We have tried to rule out any doubts and objections from potential critics.” The bacteria made it to the top only in places where there was a mycelium running through the soil. In the identical parallel experiment without a mycelium the bacteria were unable to surmount the barriers. “With this paper we have shown that there is an infrastructure.”

The fungi used in the experiment, Fusarium oxysporum, is not the only one in soil, and the pollution gobbling bacteria studied isn't the only bacteria in soil. I suspect that this capability is general. It seems obvious once you think in those terms. Fungal hyphae in uncultivated soil form a lacework that in some places for some species extends for tens and hundreds of miles. They not only actively move nutrients around, we can now see that they have a passive role as well in providing paths for other species to travel about.

The more I learn about fungi the more it seems that I ought to be inoculating my lands with desirable fungi - just to be sure that I have a well functioning rhizosphere.