Curriculum vitae

• Resistance of carbon-starved bacteria to protist grazing
• Protist biodiversity and functional role in Baltic Sea redoxclines

Suspended bacteria in marine pelagic environments are strongly influenced by both top-down (predation) and bottom-up (resources) controlling forces. Organic substrate and inorganic nutrient concentrations are generally very low, requiring physiological adaptations for efficient substrate uptake and utilisation as well as for long-term survival under carbon and energy limitation. In addition, pelagic environments offer little refuge against predation by bacterivorous protists, making the presence of resistance mechanisms a vital requisite.

One well known response to severe carbon limitation is the entry into the starvation-survival state. The physiological and molecular mechanisms of such a response have been studied in detail for a number of bacteria such as Vibrio spp, Enterobacteria and others. For these model organisms the final outcome is so-called non-growing “ultramicrobacteria” which are highly resistant against diverse stress factors (e.g., UV, chemical oxidants, high temperatures), remain viable for extended periods (from weeks to months or years) and can be recovered to normally growing cells by substrate addition.

In this study we aim to asceratin, by means of predator-prey model systems, whether the differentiation programme undergone by these bacteria also affords an increased protection against protist grazing; and eventually, asses the universality and relevance of this increased resistance or natural systems.

The water column of the Baltic Sea, is characterized in the deeper basins by pronounced vertical gradients in oxygen and redox conditions. Up to date, numerous studies have centered on the prokaryotic communities (bacteria, archaea), revealing a highly active community which mediates important biogeochemical processes in the transition zone from suboxic to anoxic waters (redoxcline). However, comparable studies on microbial eukaryotes (protists) are still largely lacking despite the general assumption that they exert a strong impact on the prokaryotic assemblages.

The aim of this project is to investigate the composition and functional role of phagotrophic protists (mainly flagellates and ciliates) along the redox gradients. The major hypotheses are: (1) that there occurs a fundamental shift in the structure of the microbial food web from oxic to anoxic/sulfidic waters, with a shift from heterotrophic nanoflagellates (HNF) to microaerophilic ciliates and bacteriophages as major agents of bacterial losses; and (2) that interactions between protists and prokaryotes, which comprise both bacterivory and symbiotic associations, impact the structure and activity of the prokaryotic communities and modulate biogeochemical processes mediated by functional guilds of prokaryotes (e.g., denitrifiers, ammonia oxidizers, sulfur oxidizers etc.).

To this aim, the quantitative species composition of phagotrophic protists will be examined by a combination of molecular techniques and classical microscopicy methods, and the grazing impact of the protist community will be assesed by means of different community manipulation and tracer experiments.

• Anderson R, Kjelleberg S, McDougald D and Jürgens K. Resistance of carbon-starved bacteria against protist grazing: species-specific patterns revealed. (submitted)

• Anderson R, Weber F, Wylezich C, Mylnikov A, Foissner W and Jürgens K. Protist diversity, distribution and bacterivory in Baltic Sea Pelagic Redoxclines (Oral) 2011 Aquatic Sciences Meeting (ASLO), San Juan, Puerto Rico.
• Anderson R, Weber F and Jürgens K. Grazing patterns in Baltic Sea Redoxclines (Poster) 29. Annual Conference of the National German Protozoology association (DGP). Düsseldorf, Germany, 2010.
• Anderson R, Mc. Douglad D, Kjelleberg S and Jürgens K. Are carbon starved bacteria more resistant to grazing by flagellates? (Oral). SAME, 11^th Symposium on Aquatic Microbial Ecology. Piran, Slovenia, 2009.
• Weber F, Anderson R, Wylezich C and Jürgens K. Protist Diversity, Distribution and Bacterivory in Baltic Sea Pelagic Redoxclines (Poster). 28. Annual Conference of the National German Protozoology association (DGP). Naumburg, Germany, 2009.
• Anderson R, McDougald D, Kjelleberg S and Jürgens K. Differential resistance to flagellate predation of two Vibrio species subjected to carbon starvation (Poster). 27. Annual Conference of the National German Protozoology association (DGP). Warnemünde, Germany, 2008.

Research funded by:

• IOW - Leibniz Institute for Baltic Sea Research
• Department of Education, Universities and Research of the Basque Government