Understanding the relative influence of immigration and species sorting in wastewater treatment systems is essential, as bacteria in influent wastewater can significantly impact treatment system functionality. This study investigated the contribution of immigration to the community assembly of different-sized microbial aggregates in a full-scale aerobic granular sludge (AGS) system using genome-resolved metatranscriptomics. Our novel analysis revealed that negative-net-growth-rate populations, which persist due to immigration, can exhibit substantial activity and potentially contribute to the AGS system’s functionality. The results also highlighted that sulfate-reducing and fermenting bacteria, along with some nitrifiers and glycogen-accumulating organisms (GAOs), were more active in the influent wastewater, serving as a continuous source of both beneficial and competing immigrants to the AGS system. Granular sludge (size >0.2 mm) demonstrated a robust capacity to resist immigration effects from competing immigrants, whereas flocculent sludge (size <0.2 mm) was more susceptible. Importantly, flocculent sludge harbored functional microbial groups such as active nitrifiers and fermentative polyphosphate-accumulating organisms (PAOs) belonging to Ca. Phosphoribacter, while granular sludge enriched for active conventional PAOs such as Ca. Accumulibacter. These findings provide valuable insights for engineers to design and operate AGS systems by optimizing microbial aggregate sizes and emphasizing the importance of influent microbial characterization in the design of wastewater treatment plants to enhance the functionality and activity of AGS systems.

Aerobic granular sludge (AGS) technology holds great promise of becoming the standard for biological wastewater treatment due to its lower energy consumption, small footprint, and high removal efficiency of nutrients compared to the conventional activated sludge processes. Different-sized aggregates have been shown to harbor a different microbial community composition. The central question is do full-scale AGS wastewater treatment plants (WWTPs) select for core microbial communities across different aggregate sizes and how these selected organisms differ between the different-sized aggregates. This study analyzed samples from nine geographically distributed full-scale AGS WWTPs that consistently perform well in terms of chemical oxygen demand (COD) and nutrient (N and P) removal. The main results showed that site-specific conditions highly influence microbial composition in smaller aggregates (< 1 mm), while larger granules form stable communities independent of WWTP location. Notably, all aggregates contained a small subset of 128–139 core OTUs that were both prevalent and abundant across all sizes. These core OTUs include key functional groups such as fermenters, aerobic heterotrophs, polyphosphate-accumulating organisms (PAOs), glycogen-accumulating organisms (GAOs), and nitrifiers, which play a crucial role in COD and nutrient removal. Additionally, an enrichment pattern was observed, with aerobic heterotrophs dominating in flocs, PAOs in small granules, and GAOs and nitrifiers in large granules. This study offers valuable insights into the core microbiome of different-sized aggregates in full-scale AGS WWTPs and highlights their potential role in overall system performance.

Introduction: Early-life stress exposure has been linked to an increased risk for the onset of mental disorders. As another factor, an individual’s genetic make-up may also tip the scale towards health or disease, with certain genetic variants mediating differential susceptibility towards the effects of early-life stress or other experiences. The current study investigated the molecular foundation of individual variation in the response to prenatal stress (PS) exposure in wildtype mice as well as in mice deficient for the serotonin (5-hydroxytryptamine, 5-HT) transporter (5-HTT). Methods: To meet this end, wildtype C57BL6/J dams were mated with 5-Htt+/- C57BL6/J males, after which they were exposed to restraint stress during the last part of gestation. In adulthood, female 5-HTT-deficient PS offspring and their wildtype littermates as well as age-matched control groups completed a behavioural test-battery, after which gene expression and histone 3 lysine 4 tri-methylation (H3K4me3) enrichment, as a marker of epigenetic programming, were measured in hippocampal tissue. Results: Dependent on the 5-Htt genotype, PS offspring showed decreased social behaviour in the 3-chamber sociability test. Notably, we observed a considerable degree of behavioural variation in the observed effect of PS in this social test, which allowed segregation into socially affected (SA) and socially unaffected (SU) mice. Genome-wide mRNA expression profiling of hippocampal tissue revealed a core set of 23 genes to be associated with genotype-specific variation in social behaviour following PS exposure. Whereas H3K4me3 levels did not show profound global changes in relation to the variable effects of PS exposure on social behaviour, the kinesin family member 14 (Kif14) gene, which displayed increased expression in socially unaffected wildtype mice, did show lower levels of H3K4me3 in those same mice, but not in any of the other groups. Discussion: All in all, differential susceptibility linked to PS exposure displayed 5-Htt genotype-dependent behavioural and transcriptomic profiles, supporting the notion of 5-HT-dependent developmental programming.

Background: Neurodegenerative disorders, including Alzheimer’s disease (AD), have been linked to alterations in tryptophan (TRP) metabolism. However, no studies to date have systematically explored changes in the TRP pathway at both transcriptional and epigenetic levels. This study aimed to investigate transcriptomic, DNA methylomic (5mC) and hydroxymethylomic (5hmC) changes within genes involved in the TRP and nicotinamide adenine dinucleotide (NAD) pathways in AD, using three independent cohorts. Methods: DNA derived from post-mortem middle temporal gyrus (MTG) tissue from AD patients (n = 45) and age-matched controls (n = 35) was analyzed, along with DNA derived from blood samples from two independent cohorts: the German Study on Ageing, Cognition, and Dementia in Primary Care Patients (AgeCoDe) cohort (n = 96) and the Dutch BioBank Alzheimer Center Limburg (BBACL) cohort (n = 262). Molecular profiling, including assessing mRNA expression and DNA (hydroxy)methylation levels, was conducted using HumanHT-12 v4 Expression BeadChip and HM 450 K BeadChip arrays, respectively. Functional interactions between genes and identification of common phenotype-specific positive and negative elementary circuits were conducted using computational modeling, i.e. gene regulatory network (GRN) and network perturbational analysis. DNA methylation of IDO2 (cg11251498) was analyzed using pyrosequencing. Results: Twelve TRP- and twenty NAD-associated genes were found to be differentially expressed in the MTG of AD patients. Gene sets associated in the kynurenine pathway, the most common TRP pathway, and NAD pathway, showed enrichment at the mRNA expression level. Downstream analyses integrating data on gene expression, DNA (hydroxy)methylation, and AD pathology, as well as GRN and network perturbation analyses, identified IDO2, an immune regulatory gene, as a key candidate in AD. Notably, one CpG site in IDO2 (cg11251498) exhibited significant methylation differences between AD converters and non-converters in the AgeCoDe cohort. Conclusion: These findings reveal substantial transcriptional and epigenetic alterations in TRP- and NAD-pathway-associated genes in AD, highlighting IDO2 as a key candidate gene for further investigation. These genes and their encoded proteins hold potential as novel biomarkers and therapeutic targets for AD.

Currently, the most cost-effective and efficient method for phosphorus (P) removal from wastewater is enhanced biological P removal (EPBR) via polyphosphate-accumulating organisms (PAOs). This study integrates a literature review with genomic analysis to uncover the phylogenetic and metabolic diversity of the relevant PAOs for wastewater treatment. The findings highlight significant differences in the metabolic capabilities of PAOs relevant to wastewater treatment. Notably, Candidatus Dechloromonas and Candidatus Accumulibacter can synthesize polyhydroxyalkanoates, possess specific enzymes for ATP production from polyphosphate, and have electrochemical transporters for acetate and C4-dicarboxylates. In contrast, Tetrasphaera, Candidatus Phosphoribacter, Knoellia, and Phycicoccus possess PolyP-glucokinase and electrochemical transporters for sugars/amino acids. Additionally, this review explores various detection methods for polyphosphate and PAOs in activated sludge wastewater treatment plants. Notably, FISH-Raman spectroscopy emerges as one of the most advanced detection techniques. Overall, this review provides critical insights into PAO research, underscoring the need for enhanced strategies in biological phosphorus removal.

This study describes a novel integration of aerobic granular sludge (AGS) with a gravity-driven membrane (GDM) system at a pilot scale with a treatment capacity of approximately 150 L per day to treat raw domestic wastewater. The treatment performance and energy consumption of the AGS-GDM system were compared to the neighboring full-scale aerobic membrane bioreactor (AeMBR), treating the same wastewater at about 4000(±500) m³ per day. The AGS-GDM system demonstrated superior nutrient (nitrogen and phosphorus) removal as compared to the AeMBR. The GDM unit was continuously supplied with AGS-treated effluent. The GDM unit started with high [ >20 L per m² per h (LMH) ] flux, which gradually declined. The flux remained quite stable after 15 days reaching 3 LMH after 35 days without any physical or chemical cleaning. Our results suggest that AGS-GDM is a viable technology for decentralized wastewater treatment and reuse in water-scarce regions. The AGS-GDM could easily replace conventional AeMBR technology in the wastewater treatment and reclamation market.

In aerobic granular sludge (AGS) systems, different-sized microbial aggregates having different solids retention time (SRT) coexist in the same reactor compartment and are subjected to the same influent wastewater. Thus, the AGS system provides a unique ecosystem to study the importance of local (species sorting) and regional (immigration) processes in bacterial community assembly. The microbial communities of different-sized aggregates (flocs <0.2 mm, small granules (0.2-1.0 mm) and large granules >1.0 mm), influent wastewater, excess sludge and effluent of a full-scale AGS plant were characterized over a steady-state operation period of 6 months. Amplicon sequencing was integrated with mass balance to determine the SRT and net growth rate of operational taxonomic units (OTUs). We found strong evidence of species sorting as opposed to immigration, which was significantly higher at short SRT (i.e., flocs and small granules) than that at long SRT (large granules). Rare OTUs in wastewater belonging to putative functional groups responsible for nitrogen and phosphorus removal were progressively enriched with an increase in microbial aggregates size. In contrast, fecal- and sewage infrastructure-derived microbes progressively decreased in relative abundance with increase in microbial aggregate size. These findings highlight the importance of AGS as a unique model ecosystem to study fundamental microbial ecology concepts.