Abstract
The activated sludge in wastewater treatment plants (WWTP) designed for enhanced biological phosphorus removal (EBPR) experiences periodically changing nutrient and oxygen availability. Tetrasphaera is the most abundant genus in Danish WWTP and represents up to 20–30% of the activated sludge community based on 16S rRNA amplicon sequencing and quantitative fluorescence in situ hybridization analyses, although the genus is in low abundance in the influent wastewater. Here we investigated how Tetrasphaera can successfully out-compete most other microorganisms in such highly dynamic ecosystems. To achieve this, we analyzed the physiological adaptations of the WWTP isolate T. elongata str. LP2 during an aerobic to anoxic shift by label-free quantitative proteomics and NMR-metabolomics. Escherichia coli was used as reference organism as it shares several metabolic capabilities and is regularly introduced to wastewater treatment plants without succeeding there. When compared to E. coli, only minor changes in the proteome of T. elongata were observed after the switch to anoxic conditions. This indicates that metabolic pathways for anaerobic energy harvest were already expressed during the aerobic growth. This allows continuous growth of Tetrasphaera immediately after the switch to anoxic conditions. Metabolomics furthermore revealed that the substrates provided were exploited far more efficiently by Tetrasphaera than by E. coli. These results suggest that T. elongata prospers in the dynamic WWTP environment due to adaptation to the changing environmental conditions.
Highlights
Engineered environments allow for the enrichment of beneficial microorganisms by applying specific environmental conditions that benefit their function
The adaptation of the microbial community to cope with dynamic conditions is exploited in modern wastewater treatment plants (WWTPs)
This species has been used as the model organism for this clade of P accumulating organisms (PAOs) as it has a relatively high similarity on 16S rRNA gene level to in situ abundant phylotypes [17]
Summary
Engineered environments allow for the enrichment of beneficial microorganisms by applying specific environmental conditions that benefit their function. Microorganisms have developed different physiological adaptations to cope with such changes in carbon and electron donor/acceptor availability and they include use of storage compounds such as polyhydroxyalkanoate (PHA), lipids, glycogen, poly-phosphate (poly-P), elemental sulphur, and nitrate [1,2,3]. By applying oxic/anoxic alternating phases and/or substrate rich and poor phases (feast-famine) as selective pressures, different microorganisms are enriched that efficiently remove carbon (C), nitrogen (N), and phosphorus (P) from domestic and industrial wastewater [2]. The general model assumes that poly-P is used for energy production during an anaerobic phase to take up carbon substrates These are stored as polyhydroxyalkanoates (PHAs) which are later oxidized aerobically in carbon-limited oxic phases for growth and poly-P regeneration. Over time P is depleted from the wastewater as the poly-P production is overall net-positive, and additional P is incorporated into the biomass
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