The microorganisms in coastal waters are so small that they are usually not visible to the naked eye. It can therefore be difficult to understand their extremely important role for the entire marine ecosystem. Li Zhao has chosen to study these organisms, to find out how they react to climate change in the ocean. She has used advanced DNA technology to show the potential of the microorganisms as descriptors of changes in the marine environment.
Text: Kristina Viklund
Li Zhao has studied both phytoplankton and bacteria and has been able to describe them in detail both in terms of taxonomy and function. She has done comparative studies between DNA analyses and the more traditional microscope analyses, and her findings have demonstrated that DNA methods can serve as a valuable complement to traditional microscope analysis.
Li Zhao has studied how marine microorganisms can give us information on changes in the environment.
The basis of the food web
Phytoplankton and bacteria may be invisible to the naked eye, but they form the very basis of the marine ecosystem. Phytoplankton are primary producers and react quickly to changes in the environment. They are therefore considered good indicators of the status of the marine environment and are studied in environmental monitoring worldwide. Heterotrophic bacteria also play an important role in the ecosystem, as they transform dissolved organic matter into living matter and nutrient re-cycling. The heterotrophic bacteria have come to play a major role in northern coastal areas, as dissolved organic matter increases in these areas as an effect of climate change.
Microscope image of phytoplankton during spring bloom. Li Zhao has compared DNA analyses with traditional microscope analysis.
Method with potential
Li Zhao has made DNA analyses of both phytoplankton and bacteria and has thus been able to get a detailed picture of both taxonomy and functions in the base of the ocean's food web. When it comes to phytoplankton, she has compared DNA analysis with traditional microscope analysis, and concluded that DNA sequencing of phytoplankton can work well as a complement to traditional microscope analysis in, for example, environmental monitoring.
Bacteria from the Gulf of Bothnia through an electron microscope.
Bacteria in a changing environment
She has asked herself how heterotrophic bacteria adapt to the environment in which they live and how they react to the environmental changes that a warmer climate leads to. To get answers, she has compared bacteria from river water and coastal water, and seen that bacteria in the river water are adapted to use terrestrial organic material, i.e. organic material originating from land. The coastal bacteria, on the other hand, are more adapted to utilize organic compounds derived from other marine organisms such as phytoplankton. Climate change leads to increased amounts of terrestrial organic matter in coastal waters, and knowledge of bacterial communities and their function is therefore very important when assessing the status of the marine environment.
Describes the species diversity
The results of Li Zhao's thesis are based on the advanced DNA analyses she has carried out on both phytoplankton and bacteria. She concludes that there is great potential in using DNA analyses in both research and environmental monitoring. The method has also developed tremendously in recent years. Previously, individual species were isolated to be analyzed. Today, entire communities can be analyzed both in terms of taxonomy and function. It also provides knowledge about the enormous diversity that exists in the marine ecosystems. During Li Zhao's thesis work, for example, she recovered over 1100 different microorganisms in the northern coastal areas of the Baltic Sea, a large portion of which had not been previously cultured or thoroughly characterized. Her work provides valuable insights into the previously unexplored microorganisms and their potential roles within the marine ecosystem.
Li Zhao defended her thesis on 26 May. Her supervisors have been professor Agneta Andersson and professor Xiao-Ru Wang, Department of Ecology and Environmental Science, Umeå University.