Introduction
In land-based recirculating aquaculture systems (RAS) the removal of nitrogenous waste is achieved via prokaryotic biodegradation. However, the spatiotemporal metabolic dynamics of microbial communities associated to this process in RAS are poorly understood (Letelier-Gordo et al., 2020). Fast and effective top-down molecular techniques might aid into better understanding these dynamics to suggest improvements in process design and operation (Vinayavekhin & Saghatelian, 2010; Xiao et al., 2019).
Methods
This pilot study evaluated the applicability of untargeted metabolomics fingerprinting to describe metabolic trends in RAS bioreactors. We compared two reactor designs, a two-stage moving bed bioreactor (MBBR) and an anaerobic batch fed sludge bioreactor (BFDR), as well as different locations within each of these (i.e., inlets vs outlets).
Results
The untargeted LCMS approach highlighted a clear differentiation in metabolic fingerprints between the two bioreactors. No difference was found within the MBBR (Fig. 1). However, two distinct metabolic fingerprints were recorded within the BFDR, one in the reactor’s sludge blanket and one in the supernatant.
Discussion
Contrarily to the initial hypotheses, MBBR signals clustered. Possible explanation can be identified in a vessel-wide distribution of a homogenous microbial community, influenced by substrate-limiting conditions and short hydraulic retention time (Torresi et al., 2018; Yang et al., 2019). Unexpectedly, the BFDR showed a significant diversity in metabolome, inferring on a significant differentiation between location-specific microbial communities. We demonstrated how untargeted metabolomics can reveal metabolic dynamics in a RAS bioreactor and at the same time confirm or deny their initial design principles.
References
Letelier-Gordo, C.O., Huang, X., Aalto, S.L., Pedersen, P.B., 2020. Activated sludge denitrification in marine recirculating aquaculture system effluent using external and internal carbon sources. Aquac. Eng. 90, 102096. https://doi.org/10.1016/j.aquaeng.2020.102096
Torresi, E., Gülay, A., Polesel, F., Jensen, M.M., Christensson, M., Smets, B.F., Plósz, B.G., 2018. Reactor staging influences microbial community composition and diversity of denitrifying MBBRs- Implications on pharmaceutical removal. Water Res. 138, 333–345. https://doi.org/10.1016/j.watres.2018.03.014
Vinayavekhin, N., Saghatelian, A., 2010. Untargeted Metabolomics, in: Current Protocols in Molecular Biology. John Wiley & Sons, Inc., Hoboken, NJ, USA, pp. 30.1.1-30.1.24.
Yang, L., Li, Y., Su, F., Li, H., 2019. A study of the microbial metabolomics analysis of subsurface wastewater infiltration system. RSC Adv. 9, 39674–39683. https://doi.org/10.1039/c9ra05290a
Xiao, R., Wei, Y., An, D., Li, D., Ta, X., Wu, Y., Ren, Q., 2019. A review on the research status and development trend of equipment in water treatment processes of recirculating aquaculture systems. Rev. Aquac. 11, 863–895. https://doi.org/10.1111/raq.12270