Late last year, my colleague Silke W and I went to Denmark for a short field trip to collect ciliates, where we were hosted by Lasse Riemann of the University of Copenhagen. The site where we collected our material was Nivå Bay, which is famous among environmental microbiologists for the several decades of studies there on sulfur-cycling by microorganisms.
Nivå Bay (above, view from birdwatching tower on a sunny day) is a shallow, sheltered bay where the water is only knee- to waist-height at low tide. Scattered between the tufts of seaweed and seagrass were some off-white, slimy films on the surface of the sediment. These are actually bacterial “veils”, which are sheets of mucus produced by bacteria that embed themselves in them. Like a veil made of lace, each sheet is punctuated by many holes. Unlike a wedding veil, these veils are not meant to hide anything. Instead, you can think of them as a sort of natural-born environmental engineering – the holes allow water to flow through, and the bacteria actively circulate water by beating their flagella. By working together in these colonies, the bacteria can set up a continuous flow of water through the veil. This flow mixes sulfide-rich water coming from below with oxygenated water from above, bringing together the chemicals that they use to generate energy.
There are different species of bacteria that have such behavior. One of them has the wonderful name Thioturbo danicus – the sulfur whirl of Denmark. It has flagella on both poles of its rod-shaped cells. In this video you can see what happens when a single cell is detached from the mucus veil – it ends up tumbling like a propeller, which probably was the inspiration for its name!
Here is a somewhat degraded veil that had been sitting around in a Petri dish for too long. Taken from its natural environment, it soon becomes overgrown with grazing protists and small animals that methodically eat up the bacteria: