Biofilters are potential hotspots for H2S production in brackish and marine water RAS

Some like it cold: the cellular organization and physiological limits of cold‐tolerant nitrite‐oxidizing Nitrotoga

“…Thus, some Nitrotoga have a similar sulfur‐metabolizing repertoire like Nitrococcus mobilis , a marine NOB reported to oxidize sulfide under oxic conditions (Füssel et al ., 2017). While the exact role of these enzymes in Nitrotoga remains to be analysed, they might be especially beneficial in marine habitats, as due to the high concentrations of sulfate in seawater (28 mM), H 2 S is readily produced in anaerobic sediment layers, and also under anaerobic or suboxic conditions in biofilters of marine RAS, with potential concentrations of >30 mg H 2 S L −1 depending on salinity, pH and organic load (Rojas‐Tirado et al ., 2021). Therefore, H 2 S might be a driving force for the abundance of Nitrotoga due to the higher tolerance level in comparison to Nitrospira in some systems (Delgado Vela et al ., 2018).…”

Estimation of nitrifying and heterotrophic bacterial activity in biofilm formed on RAS biofilter carriers by respirometry

“…Endogenous respiration (oxygen consumption rate in tap water without added substrates) relates to intracellular substrate consumption through the process of decay and hydrolysis for maintenance purposes in the absence of external substrate (van Loosdrecht et al, 2016;Rojas-Tirado et al, 2021;Zhou et al, 2013), which sets baselines for calculating exogenous respiration with respirometric methods. In conventional respirometric tests, a waiting period is required to stabilize the endogenous respiration rate of samples, and it has been reported to take 30 min for mixed bacterial cultures (Moussa et al, 2003), and 1 h to ~5 d for activated sludge (Li et al, 2019) to enter endogenous degradation rate by aeration.…”

Acute hydrogen sulfide exposure in post-smolt Atlantic salmon (Salmo salar): Critical levels and recovery

“…For the majority of animals, with the exception of a few species adapted to inhabiting H 2 S-rich areas (Tobler et al, 2016), exposure to concentrations of H 2 S in the micromolar range is considered lethal. Atlantic salmon in their natural habitat are unlikely to encounter toxic levels of H 2 S, but under production in saltwater recirculating aquaculture systems (RAS), fish may experience acute and chronic exposure to H 2 S, due to microbially produced H 2 S. RAS consists of several environments that contain different microbial communities, each of which vary in their potential for H 2 S production (Rojas-Tirado et al, 2021). Some of these communities have a high production potential for H 2 S under anaerobic conditions, during which H 2 S can reach lethal levels, and cause incidents of mass mortalities (Sommerset et al, 2020).…”