Doctoral Programme on Marine Ecosystem Health and Conservation
 The MARES Researchers and their Research
Biogeography of Rhodopirellula: physiological traits determing the biotope increment
PhD Code: MARES_13_2010:
Mobility
  • Host institute 1: P2 - Universität Bremen
  • Host institute 2: P7 - University of Plymouth
Research fields:
  • T1 - Future oceans : temperature changes - hypoxia - acidification
  • T3 - Biological Invasions
Promotor(s):
  • Jens Harder
  • Colin Munn
Contact Person and email: Jens Harder - jharder@mpi‐bremen.de

Subject description
Biological invasions involve dispersal and sucessful competition with the indigenous species in an  environment that changes nowadays more due to human activities. For microbes, a biogeography  was for a long time not existent. "Everything is everywhere, but the environment selects" has been  considered as guideline. But in recent years, the biogeography of microorganisms was shown to  exist in the form of ecotypes and regional strains. For the attached-living Rhodopirellula, a benthic  microaerophilic bacterium, we have recently demonstrated that Rhodopirellula is present as three  closely-related species in European seas, with one species in the Baltic Sea, one in the North-Atlantic  and one in the Mediterranean Sea (1). Culture-independent studies revealed that Rhodopirellula  and other Planctomycetes represent up to five percent of the microorganism in the microoxic top  sediment layer of the Wadden Sea, a hotspot of carbon turnover in marine systems encountering  naturally changing temperature, light and oxygen concentrations during the tidal cycle (2).  
The PhD project will gain insight into the biogeography of Rhodopirellula strains by culture- independent studies of marine surface sediments applying novel PCR primer. These will be  developed on the basis of eight genomes of closely related Rhodopirellula strains. The molecular  ecology study is expected to provide a high resolution biogeographic map of the actual habitats of  the three closely related Rhodopirellula species in European coastal sediments. It is required to  observe the habitat border changes in the future.  
A key question is an understanding of the physiological differences between the European  Rhodopirellula species. To study the adaptation to light, temperature, hypoxia and acidification, the cultivation has to shift from batch to chemostat cultivation. This method enables the study of   physiological capacities under environmental conditions in the laboratory. Species competition  experiments will be performed with changing conditions. The outcome will be screened by  molecular methods and reveal important physiological traits of the strains. These studies provide  insight into the chance to invade the next geographical habitat upon change in the environment.
The project requires a large sampling effort for the molecular study. This can be performed within  MARES. The first sampling for isolation and cultivation within the EU FP6 network MarBEF was very  successful (3). The project includes a stay in the School of Marine Science and Engineering  in  Plymouth. Time will be spend on sampling along the coast of England and preparation of genomic  DNA for molecular analyses. The project will use special laboratories in Plymouth that are devoted  to study the influence of light on organisms.   

References:
1. N.Winkelmann, U.Jaekel, C.Meyer, W.Serrano, R.Rachel, R.Rosselló-Mora and J.Harder (2010) Determination of the diversity of Rhodopirellula isolates from European seas by multilocus sequence analysis. Applied and Environmental Microbiology 76, 776-785
2. N.Musat, U.Werner, K.Knittel, S.Kolb, T.Dodenhof, J.E.van Beusekom, D.de Beer, N.Dubilier and R.Amann (2006) Microbial community structure of sandy intertidal sediments in the North Sea, Sylt-Rømø Basin, Wadden Sea.  Systematic and Applied Microbiology 29, 333-348.
3. N.Winkelmann and J.Harder (2009) An improved isolation method for attached-living Planctomycetes of the genus Rhodopirellula. Journal of Microbial Methods 77, 276-284

Expected outcomes
PhD thesis / publications in peer‐reviewed scientific journals / a well‐educated marine microbiologist with a knowledge in molecular ecology 

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