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K. Turnau

This complex microbial warfare is taking place in a single drop of water

Deep in the churning pools of a wastewater treatment plant, microbiologists have uncovered stealth alliances and intrigue that rival human guerilla warfare. The instigator is a microscopic fungus, and its target is rotifers, tiny common aquatic animals that also thrive in wastewater sludge.

Using light and electron microscopes, as well as techniques for staining bacteria, DNA, and other substances, the team has pieced together how the fungus, Zoophagus insidians, does its dirty work. Viewed in a single drop of water (seen above), the fungus first forms a net of thin threads called mycelia, which form a web that sprouts short, lollipop-shaped branches that trap rotifers. Bacteria gather on and inside these threads, concentrating at the tops of the lollipop surfaces, and phages and some of their DNA coat this film.

Prepped for the rotifer ambush, this sticky concoction prevents the rotifer’s escape. In what seems like a coordinated assault, fungal threads (stained green) grow into and throughout the dangling rotifer, bringing with them bacteria that begin to digest the rotifer, the researchers report this week in the International Journal of Molecular Sciences. The threads feast on the fat droplets released, then withdraw, leaving just a shell and bacteria in the depleted rotifer body. The microbes finish degrading down what’s left of the unlucky prey.

The scientists counted up to 50 dead rotifers dangling from a single fungus. They have much left to learn, but once again it seems, microbes have proved themselves way more complicated than their size implies.