Abstract
Candidatus Accumulibacter phosphatis is an important microorganism for enhanced biological phosphorus removal (EBPR). In a previous study, we found a remarkable flexibility regarding salinity, since this same microorganism could thrive in both freshwater- and seawater-based environments, but the mechanism for the tolerance to saline conditions remained unknown. Here, we identified and described the role of trehalose as an osmolyte in Ca. Accumulibacter phosphatis. A freshwater-adapted culture was exposed to a single batch cycle of hyperosmotic and hypo-osmotic shock, which led to the release of trehalose up to 5.34 mg trehalose/g volatile suspended solids (VSS). Long-term adaptation to 30% seawater-based medium in a sequencing batch reactor (SBR) gave a stable operation with complete anaerobic uptake of acetate and propionate along with phosphate release of 0.73 Pmol/Cmol, and complete aerobic uptake of phosphate. Microbial analysis showed Ca. Accumulibacter phosphatis clade I as the dominant organism in both the freshwater- and seawater-adapted cultures (> 90% presence). Exposure of the seawater-adapted culture to a single batch cycle of hyperosmotic incubation and hypo-osmotic shock led to an increase in trehalose release upon hypo-osmotic shock when higher salinity is used for the hyperosmotic incubation. Maximum trehalose release upon hypo-osmotic shock was achieved after hyperosmotic incubation with 3× salinity increase relative to the salinity in the SBR adaptation reactor, resulting in the release of 11.9 mg trehalose/g VSS. Genome analysis shows the possibility of Ca. Accumulibacter phosphatis to convert glycogen into trehalose by the presence of treX, treY, and treZ genes. Addition of trehalose to the reactor led to its consumption, both during anaerobic and aerobic phases. These results indicate the flexibility of the metabolism of Ca. Accumulibacter phosphatis towards variations in salinity.Key points• Trehalose is identified as an osmolyte in Candidatus Accumulibacter phosphatis.• Ca. Accumulibacter phosphatis can convert glycogen into trehalose.• Ca. Accumulibacter phosphatis clade I is present and active in both seawater and freshwater.
Highlights
Enhanced biological phosphorus removal (EBPR) is an important technology for the removal of phosphate fromElectronic supplementary material The online version of this article contains supplementary material, which is available to authorized users.Appl Microbiol Biotechnol (2021) 105:379–388Intracellular accumulation of osmolytes is a common mechanism for halophilic organisms to survive in saline environments
There is a large range of osmolytes that are widely conserved among organisms ranging from plants to bacteria and fungi (Yancey et al 1982; Csonka 1989; Klipp et al 2005)
Accumulibacter phosphatis was operated as described in Guedes da Silva et al (2018)
Summary
Production of osmolytes can be induced by an increase in external osmotic pressure, and release is triggered by a decrease in osmotic pressure (Guillouet and Engasser 1995; Kempf and Bremer 1998; Sauer and Galinski 1998). This behavior signifies the importance of understanding osmolyte metabolism in wastewater systems that might undergo dynamic changes in salt content of the influent, as can occur due to industrial discharges or seawater intrusion in the sewer system. Accumulibacter phosphatis under saline conditions have not been described in literature
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