Involved in the research projects: (1) Eutrofication and toxic substances, (2) Influence of increasing organic input on marine pelagic food webs, (3) Nutrient richness as a selection factor for the occurrence of predation-resistant bacteria in aquatic environments and (4) Importance of the microbial food web and productivity for the occurrence of the tularemia bacterium, Francisella tularensis, in aquatic systems.
Eutrofication and toxic substances
Eutrophication and toxic substances that are injurous to the environment constitute the greatest threats to the Baltic Sea and the Gulf of Bothnia. The effect of each of the two environmental threats is relatively well known. The combined effect of the two has not yet been studied. What happens to the toxic substances dispersed in the ecosystem at differnt levels of eutrophication?
Influence of increasing organic input on marine pelagic food webs
Phytoplankton and bacteria constitute the basic resources for the pelagic marine food web. Due to their varying sizes, they enter the food web at different levels. They also have different cell stoichiometry and molecular composition, indicating that they are of different nutritional food quality.
A global climate change has been predicted to cause increased precipitation in northern Europe, which in turn will cause increased river run-off to the coastal areas. Increased concentration of humic substances and nutrients may promote growth of bacteria rather than of phytoplankton due to decreased light levels in the water. In this project we will study how a change from a phytoplankton to bacterial based food web affect the production of higher trophic levels. The production at higher trophic levels, metazooplankton and fish, may decrease due to increased respiration losses within the food chain and due to poorer food quality of the basic resource. Such changes may be of large importance for the marine ecosystem structure and function. The tasks will be approached by combining empirical experiments and modeling.
Nutrient richness as a selection factor for the occurrence of predation-resistant bacteria in aquatic environments
One of the largest threats to aquatic environments is eutrophication. It causes a number of drastic changes in the ecosystems including alteration of the species composition and food web structure. In this project we aim to identify grazing resistant and potentially toxic bacteria, and study their response to nutrient richness. We hypothesize that increased protozoan grazing pressure, due to increased nutrient load, will trigger growth predation resistant bacteria. This would have drastic effects on the food web structure and ecosystem function. For example, the ecological efficiency of the food web will be reduced. The project will be performed by field studies in the Gulf of Bothnia and chemostat-experiments. We will isolate bacteria from nutrient poor environments (pelagic off-shore) and nutrient rich environments (benthos, nutrient rich bays), and use a simple method to identify predation resistant species. The ciliate, Tetrahymena pyriformis, will be used to test bacterial edibility. Species-specific molecular probes will be developed and used for quantification of resistant species over an annual cycle. To test if predation-resistant bacteria become promoted due to increased nutrient load, chemostat-experiments will be performed where the nutrient status is varied. The species composition of the bacterial community will be studied and the competitive advantage of predation resistant and edible bacteria tested. There may be a trade-off between being inedible and having capacity to grow at fast rate. Identification of predation resistant bacteria will allow for future studies on mechanisms leading to resistance of aquatic microorganisms.
The picture shows the ciliate Tetrahymena pyriformis, feeding on fluorescently labelled bacteria.
Importance of the microbial food web and productivity for the occurrence of the tularemia bacterium, Francisella tularensis, in aquatic systems
Eutrophication has become an increased environmental threat to aquatic systems during the latest 40 years. Eutrophication of aquatic systems causes a number of problems like changed biodiversity, toxic phytoplankton blooms and oxygen deficiency. However, recent research indicates that eutrophication also facilitate the transmission and spreading of bacteria-caused human diseases. For example, outbreaks of tularemia occur in areas adjacent to eutrophied and stagnant waters. This disease is caused by the bacterium Francisella tularensis, which infects many mammalian species including humans and rodents.
The mechanism behind the transmission and spreading of the bacterium is unknown. In this project we would like to study if the microbial food web constitutes a natural reservoir for the occurrence of F. Tularensis. This bacterium has been shown to be phagocytized by protozoa. We hypothesize the bacterium survives within the protozoan cells, and that protozoa constitute a reservoir for F. Tularensis in natural aquatic systems. We also hypothesize that eutrophication promotes the occurrence of the bacterium. We will use an experimental approach with microorganisms from natural aquatic environments, and the survival and fate of introduced F. Tularensis will be studied.
This project will provide a conceptual model on how bacteria-caused diseases may be spread in aquatic systems. This is an interdisciplinary project, which needs expert knowledge in ecology, medicine and environmental science. The outcome of the project will be important for predicting tularemia outbreaks in natural environments.
We have constructed a destabilized GFP variant in F. Tularensis strain LVS (Live Vaccine Strain) that we use for survival studies in different hosts. This strain is fluorescently labeled by the insertion of a fluorescing plasmid. We have demonstrated that F. Tularensis can infect and survive in free-living amoeba such as Acanthamoeba castellanii. The results also showed survival of F. Tularensis in amoeba cysts, which may be important for the transmission of the microorganism. Furthermore, preliminary results show that flagellates (Bodo sp.) take up F. Tularensis as well.
We have together with Prof. Anders Sjöstedt’s group at Dept. Of Bacteriology, Umeå University, recently initiated a 3-year field epidemiological study of F. Tularensis in two endemic areas in Sweden, Ljusdal and Örebro. Ljusdal is the area with highest incidence of the disease in Sweden, and maybe in the whole world. In this area, there are reports of human and animal cases of tularemia virtually every year and during the last 5 years there have been 3 major outbreaks. In addition, we also collect samples in one emergent area, the Örebro region, in cooperation with Dr. Erik Bäck. We have collected samples from water, mud, rodents and mosquitoes. So far, F tularensis have been identified and isolated from water samples in Ljusdal and from a water rat in Örebro.