Tesi Master
Scadenza: 01 giugno 2020
The objective of the study is to test the correlation between the intensity of bioconvection and (i) the intensity of zooplankton grazing on other PSBs and GSBs and (ii) the sedimentation rate of bacterial cells.

Tesi Master in Ecologia Microbica

Lake Cadagno is a crenogenic meromictic lake located at 1921 m asl. in the Piora valley, in the southern part of the Swiss Alps (46°33’ N, 8°43’ E). The permanent stratification allows the development of a dense community of anaerobic phototrophic sulfur bacteria (Danza et al. 2018), which uses reduced sulfur compounds as electron donors for CO2 fixation (Storelli et al. 2013; Luedin et al. 2019). The motile purple sulfur bacterium (PSB) Chromatium okenii can mix small portion of water by a mechanism called bioconvection (Sommer et al. 2017). Indeed, when such microorganisms accumulate locally in a layer, the density of the water increases. This layer of heavier water on top of lighter water sinks and mixes with the surrounding water. Continuous upward swimming provides the energy to maintain the water motion. However, the details on the environmental drivers and the ecological consequences are still unknown. Bioconvection could thus be an important evolutionary mechanism that increases the competitive advantage of C. okenii, against other microbial taxa presents in the chemocline of Lake Cadagno, with higher affinity to light and H2S such as green sulfur bacteria (GSB) or with greater ability to fix CO2 both in the light and dark such as small-celled PSB (SNF BIOCAD project). From an ecological point of view, bioconvection and the activity of microbial species in the chemocline of Lake Cadagno, likely has consequences on biogeochemical cycles and trophic interactions that are relevant for other compartments of the lake ecosystem, such as phyto- and zoo-plankton communities and sedimentation and degrading process.

  • Does bioconvection alter interactions of the microbial community with zooplankton grazers at the upper limit of the chemocline?
  • Does bioconvection alter sedimentation rate of the PSBs and GSBs other than C. okenii?

 

AIM OF THE STUDY

The objective of the study is to test the correlation between the intensity of bioconvection and (i) the intensity of zooplankton grazing on other PSBs and GSBs and (ii) the sedimentation rate of bacterial cells. The trophic links between PSB Chromatium okenii, Thiodictyon syntrophicum and GSB Chlorobium pheobacteroides, respectively, and their zooplankton grazers in response to bioconvection will be established and quantified based on gut content analysis of grazers using species-specific FISH probes. Sedimentation of PSB and GSB will be quantified as well using sediment traps installed below the chemocline using the mooring and allowing cumulative sampling in two-week intervals. Measurement of PSB and GSB abundance and chemical (% C, N, S) composition of the sediment to determine the influence of bioconvection on the sedimentation rate of phototrophic sulfur bacteria from the photosynthetic zone (low oxygen and enough sulfide and light).

 

CONTACT

We are looking for a motivated environmental science student interested to work also in the field during several sampling on the meromictic Lake Cadagno (http://www.cadagno.ch/). The principal place of work will be in Bellinzona at the Laboratory of applied microbiology (LMA) from University of Applied Sciences and Arts of Southern Switzerland (SUPSI).

For further information, please contact Nicola Storelli (Microbial ecology - Lake Cadagno)

st.wwwsupsi@supsi.ch