PhD students

PhD students and projects at DTU Aqua within the research area Aquaculture.

Alexandre Nguyen-tiêt

Title of the PhD project
Characterization of H2S producers in Recirculating Aquaculture Systems (RAS)

Supervisors
Sanni-Leea Hellevi Aalto, Lars-Flemming Pedersen & Stefan Bertilsson

Background of the project
Hydrogen sulfide (H₂S) is an extremely toxic compound for organisms, preventing aerobic respiration. In marine land-based recirculating aquaculture systems (RAS), H₂S production is a major challenge, leading to fish mortality and thus important economic consequences. Because of the high sulfate (SO₄^2-) and organic matter concentration present in marine RAS, H2S production has been associated with the sulfate-reducing bacteria (SRB). However, there are also other pathways for producing H₂S that could play a significant role but are currently neglected, e.g. some bacteria have the capacity to degrade the cysteine to produce pyruvate, ammonia and H₂S. In both marine and freshwater RAS, cysteine is present, originating from the uneaten feed and feces of fish, suggesting that cysteine degradation could be an important H₂S source in aquaculture environment.

About the project
The main goal of this PhD project is to gain knowledge on the bacterial communities responsible of H₂S production in RAS and especially the cysteine degrading bacteria. To do so, I will first enrich and cultivate H₂S producing bacteria from samples collected at several locations in RAS. After that, I will use metagenomic/metatranscriptomic analysis to identify the bacteria as well as the metabolic pathways responsible of H₂S production and develop primers to examine H₂S production dynamics and microbiology in aquaculture biofilms.

Perspectives
The results obtained through this project will give a better understanding of the microbial community responsible of H₂S production in land-based aquaculture. With this new knowledge, I can develop ways to quantify and monitor both the traditional (SRB) and cysteine-degradation H₂S producers in RAS to avoid production losses related to H₂S exposure and to promote safe and stable fish production in the future.