Cyanobacteria were among the first organisms to produce oxygen, which meant they were a significant milestone in the evolution of plants and animals. Countless species of cyanobacteria inhabit almost all habitats around the world. For her doctorate at Eawag, Marie-Eve Monchamp analysed sediment cores from ten different lakes around the fringes of the Alps, thus gaining an insight into the communities of cyanobacteria living over the past 100 years.
The lakes in the perialpine regions of Europe are home to a particular community of cyanobacteria which Marie-Eve Monchamp investigated in connection with her doctoral thesis at Eawag. “We collected sediment cores from ten lakes in Switzerland, Italy and France, and analysed the cyanobacterial DNA extracted from these cores”, she explains. Monchamp and her team were able to use the data to then reconstruct the time and place that the bacterial communities lived. They established that although the overall number of different species in the lakes had not significantly decreased over the past 100 years, the communities across the various lakes became more and more homogeneous as time went on. The species that benefited the most from the changing conditions in the lakes were those that were able to adapt quickly. This can be problematical, as “it is these species, in particular, that are often toxic”, says Monchamp.
Temperature affects species diversity
The researchers have now drilled down further into the data to find out whether and how human activity affects the biodiversity of these cyanobacteria, and to investigate questions such as whether detergent and fertiliser run-offs affect the cyanobacteria communities, and how the bacteria react to rising temperatures.
The researchers represented the communities of cyanobacteria found in the sediment cores in the form of a phylogenetic tree. Monchamp explains: “Where the species are randomly distributed around the branches of the phylogenetic tree and no clear pattern can be identified, nothing seems to affect their diversity. However, where they are grouped, or distributed extremely evenly, this is an indicator that they are very susceptible to external influencing factors.”
The photosynthesizing cyanobacteria in the ten lakes seem to be moderately affected by external circumstances: In 44 out of 76 species, just over half of the family trees studied were grouped, and the rest were randomly distributed. Comparisons with data on water quality and temperature led the researchers to the conclusion that temperature, especially, was a factor that worked in favour of some species and led to the disappearance of others. “From earlier analyses, we had realised that the stability of the water stratification is also important”, Monchamp adds. Nutrients such as phosphorus and nitrogen on the other hand did not seem to have an impact on the diversity of the cyanobacterial community.