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Community Dynamics and Phenotypic Changes of Limnic Bacteria During Experimental Manipulation of Bottom-up and Top-down Factors (COMPLEX)
Start date: Jul 1, 2009, End date: Oct 31, 2010 PROJECT  FINISHED 

"Bacteria in freshwaters are key players in the degradation of organic carbon. Their important functional role is related to the specific growth features of different genotypes within mixed assemblages. Limitation by substrates and nutrients (bottom-up factors) and high predation by bacterivorous protists (top-down factors) together shape the composition of microbial assemblages. Bacterial species have developed strategies that are either aimed at maximizing their competitive abilities for bottom-up limitations or at resisting protistan top-down control. Both specializations conceivably also represent trade-offs, either of metabolic versatility or of growth efficiency. We propose studying the effects of different types of growth limitations (carbon and phosphorus) on experimental assemblages of freshwater bacteria in the presence and absence of predation. Particular focus will be put on the relationship between the diversity and the metabolic function of the bacterial communities. Representatives of key populations will be isolated and tested for physiological versatility, growth efficiency and sensitivity to chemical cues (kairomons) by the predator. The growth of isolates and their response to predation will also be determined at close to natural conditions. The proposed work will provide novel insight into the specific metabolic differences of freshwater bacteria that are most successful at either top-down or bottom-up selection. It will also produce new physiologically well characterized model strains to study chemical interactions between bacteria and predators. The project will combine the research proficiency of the applicant with the ample facilities and the expertise available at the host institution. The candidate will benefit from a research environment that offers possibilities for fruitful collaborations. Moreover, it will be advantageous for his envisaged career to gain teaching experience in a university environment."

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