The deep waters of Lake Tanganyika lack oxygen, and are thus devoid of most life. However, they are home to bacteria that are essential to the lake's food web.Credit: Image Professionals GmbH / Alamy Stock Photo
The microorganisms that inhabit Africa’s Lake Tanganyika play a critical role in sustaining the lake’s ecosystem. The identity of these microorganisms and their exact roles in cycling nutrients throughout the lake has, however, gone unstudied. Now, scientists from the US, Germany, and Tanzania, have shone a light into the darkness of the lake’s waters.
Lake Tanganyika holds 16% of the world’s freshwater, and is the largest tropical freshwater lake on Earth. The sharp depth of the lake causes it to be stratified — meaning its layers of water don’t mix. This results in a ~70m-deep, oxygenated surface layer topping a ~1400m-deep abyss of oxygen-depleted water.
The microorganisms that inhabit these anoxic waters play a crucial role in the biogeochemical cycling of nutrients, such as carbon, nitrogen, and sulphur, throughout the food web of the ecosystem. “When microbes utilise these nutrients, they make them available to other organisms,” explains lead researcher, Patricia Tran, from the University of Wisconsin-Madison in the United States.
Tran and her team collected samples from two regions on Lake Tanganyika at differing depths. From the samples, the researchers reconstructed the genomes of more than 500 microorganisms. The team also reconstructed the nutrient metabolism of the microorganisms as a community and as single-microbes.
Tanganyika offers a “model ecosystem,” due to the vast species in its oxygenated surface waters, says principal investigator, Karthik Anantharaman, also at the University of Wisconsin-Madison. Their work has revealed the missing “microbial resolution” of the lake, and provides a baseline for future studies of the lake.
