Parasitic fungi keep harmful blue-green algae in check

Date:
June 9, 2020
Source:
Forschungsverbund Berlin
Summary:
When a lake is covered with green scums during a warm summer,
cyanobacteria -- often called blue-green algae -- are usually
involved.

Mass development of cyanobacteria is bad for water quality. But
cyanobacteria can become sick, when for instance infected by
fungal parasites. Researchers found out that these infections do
not only kill cyanobacteria, they also make them easier to consume
for their natural predators. Fungal parasites thus help to slow
down the growth of blue- green algae.



FULL STORY ==========================================================================
When a lake is covered with green scums during a warm summer,
cyanobacteria - - often called blue-green algae -- are usually
involved. Mass development of such cyanobacteria is bad for water quality because they can deprive the water of oxygen and produce toxins. But cyanobacteria can become sick, when for instance infected by fungal
parasites. Researchers from the Leibniz-Institute of Freshwater Ecology
and Inland Fisheries (IGB) found out that these infections do not only
kill cyanobacteria, they also make them easier to consume for their
natural predators. Fungal parasites thus help to slow down the growth
of blue-green algae.


========================================================================== Blue-green algal blooms are an increasing problem in waterbodies
worldwide: Higher temperatures and growing nutrient loads lead to
excessive growth of cyanobacteria. These mass developments affect water
quality because many cyanobacteria produce toxins and reduce the oxygen concentration in the water, sometimes leading to death of fish and other aquatic organisms.

The international team led by IGB found that algal growth can
be controlled by parasitic fungi. "Many of these algae have long
filamentous shapes or grow in colonies, which makes them difficult
to be eaten by their natural predators," explains Dr. Thijs Frenken,
first author of the study and researcher at IGB and the University
of Windsor in Canada. Chytrids, a very common group of fungi, often
infect cyanobacteria. The researchers have now shown that, in addition
to infecting and killing algae, the fungi "chop" the algae into shorter
pieces, making them easier to be eaten by small aquatic organisms. "We
knew that fungal infections reduce the growth of cyanobacteria, but
now we know that they also make them easier prey," says IGB researcher
Dr. Ramsy Agha, head of the study.

Fungi as food supplements for zooplankton The researchers showed that in addition to "chopping" infected cyanobacteria filaments and making them
more vulnerable to predation by small organisms in the water, zooplankton, parasitic fungi themselves serve as a valuable food supplement. Chytrid
fungi contain various fats and oils that are an important part of the
diet of small freshwater organisms and are not present in blue- green
algae. Parasitic fungi therefore serve as an important dietary connection between different levels of aquatic food webs.

"These results show how parasites, although usually perceived as something
bad, also have important positive effects on the functioning of aquatic ecosystems," says Professor Justyna Wolinska, head of the IGB research
group Disease Evolutionary Ecology.


========================================================================== Story Source: Materials provided by Forschungsverbund_Berlin. Note:
Content may be edited for style and length.


========================================================================== Journal Reference:
1. Thijs Frenken, Justyna Wolinska, Yile Tao, Thomas Rohrlack,
Ramsy Agha.

Infection of filamentous phytoplankton by fungal parasites enhances
herbivory in pelagic food webs. Limnology and Oceanography, 2020;
DOI: 10.1002/lno.11474 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2020/06/200609111050.htm

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