Em. Prof. dr. Riks Laanbroek

 

1975     MSc in Biology at the State University of Groningen (the Netherlands); subjects General, Medical and Biochemical Microbiology

  

 

2009 to date Senior Scientist NIOO - KNAW 

2008 to date Research Associate Smithsonian Institute, Washington

2004 – 2016  Professor in Microbial Ecology of Wetlands, Utrecht University 

2001 – 2009 Director NIOO – Centre for Limnology, Nieuwersluis

1993 – 2001 Director of Science NIOO – Centre for Limnology, Nieuwersluis

1990 – 2005 Private chair in Soil Biology, Radboud University, Nijmegen

1985 – 1993 Head Department of Soil Biology, Institute of Ecological Research, Heteren

1983 – 1985 Scientist, Delta Institute for Hydrobiological Research, Yerseke

1980 – 1983 Post doc, State University of Groningen

1979 – 1980 Post doc, Georg August Universität, Göttingen, Germany 

 

 

Editor FEMS Microbiology Ecology

 

 

• Niche differentiation within microbial groups performing key geochemical processes

The microbial world can be subdivided in groups responsible for performing specific functions in the ecosystem, among which biogeochemical processes. Members of a functional group are likely to differ among each other in the rate at which they perform a particular process and in their responses to environmental conditions, thereby providing a potential link between group composition, niche differentiation and rates of biogeochemical processes. Microorganisms with overlapping functional traits are the appropriate model organisms to assess the significance of diversity for geochemical fluxes and to test general ecological principles such as adaptation through phenotypic plasticity and genotypic changes. Ammonia-oxidizing and sulfate-reducing microorganisms have been chosen to study niche differentiation within microbial groups performing key geochemical processes. Ammonia-oxidizing microorganisms are at the beginning of many environmental problems such as eutrophication, groundwater pollution, greenhouse gas emissions and soil acidification. By the production of sulfide, sulfate-reducing micro-organisms are involved in the immobilization of metals and in the internal phosphate eutrophication  

 

• Ammonia-oxidizing microorganisms

Aerobic ammonia-oxidizing microorganisms belong to the proteobacteria or the thaumarchaea. They share the ability to oxidize ammonia to nitrite and hence link the reduced and oxidized parts of the global nitrogen cycle. In contrast to the already long-known proteobacteria, relatively less is known about the recently discovered ammonia-oxidizing thaumarchaea, although their amoA genes outnumber those of the proteobacteria in many habitats suggesting an important role in the global nitrogen cycle. The diversity of the proteobacteria is restricted to only small number of species. However, the species behave in different ways with respect to environmental conditions, which indicate niche differentiation between the species. In the Scheldt estuary, for example, the dominant freshwater species is replaced by a salt-tolerant species. Surprisingly, the salt-tolerant species grows better under freshwater conditions compared to brackish circumstances, but are apparently overgrown by the others in the freshwater part of the estuary. It is not know if replacement of species has consequences for the rate of ammonia oxidation in the ecosystem. This question is tackled by studying the distribution of species in different environments by application of genetic methods aiming at specific phylogenetic or functional genes and by linking the patterns of distribution to patterns of physical and chemical characteristics. In addition, the behavior of isolated species is studied in model systems under controlled conditions in the laboratory. In this way, chemolithotrophic ammonia-oxidizing microorganisms are good model organisms for studying a possible relation between species identity and ecosystem functioning.

 

• Sulfate-reducing microorganisms

With respect to habitat, physiology and diversity, sulfate-reducing microorganisms are just the opposite of ammonia-oxidizing microorganisms. They thrive in anoxic environments, they require organic compounds for the generation of energy and they are much more diverse. However, despite the differences, the ecology of sulfate-reducing and ammonia-oxidizing microorganisms is studied in a similar way by looking to their distribution in different environments with the application of genetic tools based on a functional gene, and by investigating these microbes in model systems under controlled conditions in the laboratory.

 

 

 

Frank Verhagen (PhD thesis 1992), Willem Engelaar (1994), Paul Bodelier (1997), Ronald Kester (1997), Joke Nijburg (1998), Erik van Hannen (1999), Jaco van der Nat (2000), Arjen Speksnijder (2000), Monique de Bie (2002), Jody de Brouwer (2002), Nicole Wrage (2003), Marco Dignum (2003), Marc Staal (2003), Jolanda Verspagen (2006), Stefan Simis (2006), Martijn Antheunisse (2007), Marjolijn Tijdens (2007), Manuela Coci (2007), Marzia Miletto (2007), Juanjuan Wang (2011), Liesbeth Vissers (2012), Susann Vollrath (2012), Anne Steenbergh (2012), Joost Keuskamp (2014) and Anne Daebeler (2014).