Trichodesmium filaments can combine to form aggregates called puffs
Florida Fish and Wildlife Conservation Commission
One of the most abundant and important types of photosynthetic bacteria in the ocean may owe its success to teamwork.
bacteria called Trichodesmiumcan actively combine to form larger aggregates or break apart in response to changing environmental conditions, Ulrike Pfreund of the ETH Zurich in Switzerland and colleagues found .
“This behavior is probably the key to why.” Trichodesmium Very plentiful and very successful,” says Pfreund.
Trichodesmium A group of cyanobacteria of several species. Because its members often form reddish-brown flowers, they are sometimes called sea sawdust, which may be the origin of the Red Sea name.
These bacteria not only provide food for other organisms, but also convert atmospheric nitrogen into chemicals that other photosynthetic organisms can use. According to Freund, these plants are fertilizing vast oceanic areas that would be too nutrient-poor to grow anything.
“Essentially, it’s a living fertilizer for the ocean,” she says. “They provide most of the sequestered nitrogen in the ocean, and many other organisms that sequester CO2 depend on this nitrogen.”
Trichodesmium It grows in hair-like filaments up to several hundred cells long. Filaments may be individually suspended, but often occur in colonies or aggregates, each containing up to several hundred filaments.
These aggregates can be 1-2 millimeters in diameter and are visible to the naked eye. Some aggregates, called puffs, have filaments that radiate from the center like pom-poms. In others, called tufts, the filaments are parallel like hair bundles.
Aggregation has been shown to help Trichodesmium You get the iron you need from the dust. But how the aggregates form has been a mystery, says Pfreund. There is also the idea that the filaments simply stick together if they hit each other, but this does not explain the organized appearance of the filaments. Another thing is that they grow up like this.
while growing up Trichodesmium In the lab to study the genome, Freund noticed that the appearance of the aggregates could change completely during the day, and suspected an active process was involved. She and her colleagues confirmed this and performed a series of experiments to show how it happens.
The filaments can slide along the surface, and when two filaments come into contact, they can start sliding along each other, much like two trains using each other as tracks. If this process continues indefinitely, Pfreund says, the filaments will completely slide off each other. Therefore, when the bacteria want to stay in the aggregate, they keep reversing direction.
To make the aggregates more tightly bundled, she found that reversal occurred more frequently, maintaining greater overlap of the filaments. Loosening them will reduce the frequency of reversals.
The researchers found that loosening and tightening of this aggregate can occur in just a few minutes in response to changes in light levels. Very bright light can damage the photosynthetic machinery, and tighter aggregates reduce the light level to which each filament is exposed.
At sea this might be useful Trichodesmium Deal with the sun coming out or hiding behind clouds.
Freund believes this loosening and tightening also helps the aggregates control buoyancy, allowing them to move up and down as needed. Trichodesmium When this nutrient is depleted at the surface, it is known to migrate deeper to obtain phosphate.
“The reversal mechanism is Trichodesmium Richard Kirby, an independent plankton scientist and author, said that loosening and tightening aggregates to affect density, buoyancy and light gain may have contributed to the success of this species. There is.”
Freund et al. also found that the puffs were not composed of different strains as previously thought, but rather formed by coalescing clusters. But many questions remain open, such as how the filaments slide and how they know when to flip.
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