Determinants of Community Structure, Function and Succession of Freshwater Microorganisms Colonizing Lake Snow

• Applicant: Dr. Mina Bizic
• Subject Area: Microbial Ecology and Applied Microbiology
• Term: from 2017 to 2024
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 393798666

In the proposed research, I aim to conduct a temporal study on the microbial degradation of macroscopic organic aggregates in freshwater lakes, also known as Lake Snow. I will study Lake Snow at near-in-situ conditions using a flow-through rolling tank we have recently developed. I aim to determine the factors responsible for microbial succession on sinking / degrading particles while accounting for single particle heterogeneity both in community composition as well as in activity. Lake Snow makes up a significant portion of the aquatic particulate organic matter and consists of different source particles (e.g. phytoplankton cells, zooplankton-carcasses and allochthonous organic matter). Concentrations of organic and inorganic molecules, on Lake Snow, often exceed background levels by 2-4 orders of magnitude providing associated microorganisms with a potent energy, carbon and nutrient source. As a result, these particles are heavily colonized by heterotrophic bacteria that play an essential role in their degradation. The community structure of these bacteria differs between individual particles, but yet the driving force behind this observation has not been studied. The microbial community on particles changes in time, a succession process attributed to changes in carbon quality; my preliminary results, however, show no changes in expression of related microbial genes over at least 8 days. Therefore, I hypothesize that a major force in shaping the particle-associated community is inter-organisms interactions. These include Bacteria-Eukarya, Bacteria-Bacteria and Bacteria-Viruses interactions. To evaluate the fate of Lake Snow under natural conditions as well as to achieve a better understanding of the processes determining the nature of the associated microbial community in space and time, I plan to: A) Determine the effects of particle sources on microbial colonization heterogeneity; B) Determine the heterogeneity in microbial activity among particles of the same and different source; C) Assess the contribution of inter-organisms interactions to succession events of Lake Snow colonizing microbial communities in comparison to changes in carbon quality. To address all topics, I will study multiple, lab-made, individual particles using novel flow-through rolling tank systems coupled with community fingerprinting, activity measurements, transcriptomics and organic matter characterization. The results of this study will provide crucial knowledge on microbial mechanisms at the microscale to better understand the role of aquatic systems in organic matter cycling and storage.

• DFG Programme: Research Grants