Are fungi Bacteria
Credit: TheAlphaWolf Red parent bacteria and the green offspring of bacterial mating (conjugation) coat this filament of Pythium that bridges an air gap between parental bacterial cultures. Credit: Berthold et al. 2016
The scientists wondered how important fungal filaments are in facilitating bacterial sex in soil of differing navigability. To that end, they prepared laboratory agar gel in three different ways so as to make it easy, moderately hard, or difficult for the bacteria to travel on it. They then tested the ability of bacteria to mate on these surfaces in the presence or absence of Pythium. In environments where bacterial travel was easy, there were not much more horizontal gene transfer going in the presence of Pythium than without it.
But when the gel the bacteria were grown on made it harder to get around, bacteria piled on to Pythium’s filaments. As a result, they mated more, simply because they were much more likely to bump into each other. This experiment underscores the chief reason that the fungal highway encourages conjugation, the authors say: it reduces the volume of water in which bacteria can travel, and consequently increases the odds they will meet.