Understanding the causes for blooms of potentially harmful bacteria in a protected coastal lagoon in Uruguay

This project has supported the collaboration between the Microbiology Department of the Institute for Biological Research IIBCE, Montevideo, Uruguay, and the Department of Limnology, Institute of Plant Biology, University of Zurich, through a short-term visit of Dr. Cecilia Alonso. The long-term collaboration between the two partner laboratories is focused on the ecological factors that lead to sudden blooms of potentially harmful bacteria in coastal Uruguayan lagoons, or of bacteria that might serve as indicator species for environmental alteration. Such blooms are an only recently discovered phenomenon whose causes, development, and potential environmental implications are still poorly understood. For this purpose it is essential to experimentally establish those environmental parameters that specifically favor the growth of different microorganisms. The stay allowed for the evaluation of samples from experimental field work (conducted in Uruguay in 2007) by means not available in the IIBCE laboratory due to high costs and technological restraints.
The experiments analyzed during Dr. Alonso’s sojourn were designed to elucidate how the hydrology of two lagoon systems would affect the development of different bacterial groups, and eventually lead to a bloom of particular bacterial populations in the lagoons. In these experiments, water from the two hydrological zones of each lagoon was taken and subsequently mixed at different proportions. The response of the different bacterial groups was evaluated in terms of changes in abundances and changes in activity by using a combination of whole cell identification by Fluorescence in Situ Hybridisation with rRNA-targeted oligonucleotide probes and microautoradiography for the microscopic detection of metabolic activity. The mixing of freshwater from the northern zone of the first lagoon (Laguna de Rocha) with the brackish water from the southern zone stimulated all bacterial groups present in the system. However, the degree of mixing in which this stimulation reached its maximum was characteristic of the particular bacterial groups: Proteobacteria seemed to be stimulated by a wide range of mixing conditions, while Bacteroidetes appeared to need a distinctive ratio of freshwater to brackish water to be stimulated. In the second lagoon (Laguna de Castillos) betaproteobacterial cells were stimulated by all mixing conditions whereas the Actinobacteria were only stimulated at high proportions of turbid water, indicating contrasting physiologies of the 2 main bacterial groups of this community.
The visit of Dr. Alonso also served for the planning of a joint experiment and of a postgraduate course in Uruguay during December 2008, the latter being conducted in cooperation with several South American educative and research institutions.

 

Abbildungsbeschriftungen:

Laguna_Rocha01.jpg: Arial photograph of Laguna de Rocha showing the sandbar that separates the lagoon from the open ocean.

Laguna_Rocha02.jpg: Photomicrograph of a bloom of potentially harmful bacteria in the lagoon (in green) colonizing an algal cell (in blue).

Partner Institutions:

Switzerland: University of Zurich
Institute of Plant Biology
Department of Limnology
Seestr. 187
CH-8802 Kilchberg, ZH

Uruguay: Instituto de Investigaciones Biológicas Clemente Estable.
Departamento de Microbiología.
Av. Italia 3318
Montevideo

Contact persons

Switzerland: Prof. Dr. Jakob Pernthaler.
Tel: +41 44 716 1210
Fax: +41 44 716 1225
e-mail: pernthaler@limnol.uzh.ch

 

Uruguay: Dr. Cecilia Alonso.
Tel: +598 2 487 16 16 ext 148
Fax: +598 2 486
e-mail: calonso@iibce.edu.uy