PHA stimulated denitrification through regulation of preferential cofactor provision and intracellular carbon metabolism at different dissolved oxygen levels by Pseudomonas stutzeri

Long-term effects of dead algal deposition on sediment surfaces: Behavior of endogenous phosphorus release in sediments

Algae blooms are frequently triggered owing to the improvements in aquatic trophic levels. The aggregated algae from these blooms are eventually dead and accumulate on sediment surfaces, impacting the microenvironment and phosphorus cycling in aquatic systems. However, research on the effects of naturally dead algal deposition on endogenous P release from sediments is lacking. In this study, we investigated the long-term effects of dead algal deposition at varying concentrations on P release from sediments and the underlying mechanisms by assessing microbial metabolism and community structure. The results showed that following the dead algal deposition, the release of P from sediments to the water column peaked on day 40 (0.14±0.017 mg L-1 in Amend12) and the SRP exchange capacity reached maximum (6.09 ± 1.63 mg/(cm2·d) in Amend12) at sediment-water interface in phase1 (0-3 day). This might be primarily attributed to the deposition of dead algae introducing much organic matter (such as organic carbon and organic phosphorus), thus altering the sediment microenvironment, which increased the activity of phosphorus-cycle microorganisms, such as polyphosphate-accumulating organisms, through increasing C source metabolism, reducing intracellular ammonia inhibition, and creating more suitable anaerobic conditions. Therefore, this study has improved our understanding of the management strategies for controlling endogenous phosphorus release in eutrophic shallow lakes, suggesting that the priming effects of freshly deposited algae could be mitigated by harvesting algae at the peak of blooms.

The enhancement effect of n-Fe3O4 on methyl orange reduction by nitrogen-fixing bacteria consortium

Although the anaerobic reduction of azo dyes is ecofriendly, high ammonia consumption remains a significant challenge. This work enriched a mixed nitrogen-fixing bacteria consortium (NFBC) using n-Fe3O4 to promote the anaerobic reduction of methyl orange (MO) without exogenous nitrogen. The enriched NFBC was dominated by Klebsiella (80.77 %) and Clostridium (17.16 %), and achieved a 92.7 % reduction of MO with an initial concentration of 25 mg·L-1. Compared with the control, the consortium increased the reduction efficiency of MO, cytochrome c content, and electron transport system (ETS) activity by 11.86 %, 89.86 %, and 58.49 %, respectively. When using 2.5 g·L-1 n-Fe3O4, the extracellular polymeric substances (EPS) of NFBC were present in a concentration of 85.35 mg·g-1. The specific reduction rates of MO by NFBC were 2.26 and 3.30 times faster than those of Fe(II) and Fe(III), respectively, while the enrichment factor of the ribosome pathway in NFBC exceeded 0.75. Transcriptome, carbon consumption, and EPS analyses suggested that n-Fe3O4 stimulated carbon metabolism and secreted protein synthesized by the mixed culture. The latter occurred due to the increased activity of consortium and the content of redox substances. These findings demonstrate that n-Fe3O4 promoted the efficiency of mixed nitrogen-fixing bacteria for removing azo dyes from wastewater. This innovative approach highlights the potential of integrating nanomaterials with biological systems to effectively address complex pollution challenges.

Polyhydroxyalkanoate production from fermentation of domestic sewage sludge monitoring greenhouse gas emissions: A pilot plant case study at the WRRF of Palermo University (Italy)

This paper presents a comprehensive study on polyhydroxyalkanoate (PHA) production from sewage sludge. Greenhouse gas (GHG) emissions were monitored for the first time to assess the impact of climate change and environmental sustainability. The pilot plant was composed of a fermenter with a membrane and two biological reactors (namely, selection and accumulation). Results showed that despite a low organic loading rate (namely, 0.06 kg BOD kg SS-1 day-1), a good PHA yield was obtained (namely, 0.37 g PHA/g volatile fatty acids), confirming that sewage sludge can be a suitable feedstock. GHG emissions were 3.85E-04 g CO2eq/g and 32.40 g CO2eq/g, direct and indirect, respectively. Results provided valuable insights in view of finding a trade-off between PHA production and GHG emissions to prove the PHA production process as an effective solution for biosolids disposal at a low carbon footprint.

How β-Cyclodextrin-Functionalized Biochar Enhanced Biodenitrification in Low C/N Conditions via Regulating Substrate Metabolism and Electron Utilization

Biodenitrification plays a vital role in the remediation of nitrogen-contaminated water. However, influent with a low C/N ratio limits the efficiency of denitrification and causes the accumulation/emission of noxious intermediates. In this study, β-cyclodextrin-functionalized biochar (BC@β-CD) was synthesized and applied to promote the denitrification performance of Paracoccus denitrificans when the C/N was only 4, accompanied by increased nitrate reduction efficiency and lower nitrite accumulation and nitrous oxide emission. Transcriptomic and enzymatic activity analyses showed BC@β-CD enhanced glucose degradation by promoting the activities of glycolysis (EMP), the pentose phosphate pathway (PPP), and the tricarboxylic acid (TCA) cycle. Notably, BC@β-CD drove a great generation of electron donors by stimulating the TCA cycle, causing a greater supply of substrate metabolism to denitrification. Meanwhile, the promotional effect of BC@β-CD on oxidative phosphorylation accelerates electron transfer and ATP synthesis. Moreover, the presence of BC@β-CD increased the intracellular iron level, causing further improved electron utilization in denitrification. BC@β-CD helped to remove metabolites and induced positive feedback on the metabolism of P. denitrificans. Collectively, these effects elevated the glucose utilization for supporting denitrification from 36.37% to 51.19%. This study reveals the great potential of BC@β-CD for enhancing denitrification under low C/N conditions and illustrates a potential application approach for β-CD in wastewater bioremediation.

Effect of oxic and anoxic conditions on intracellular storage of polyhydroxyalkanoate and polyphosphate in Magnetospirillum magneticum strain AMB-1

Magnetotactic bacteria (MTB) are microorganisms widely inhabiting the oxic-anoxic interface of aquatic environments. Beside biomineralizing magnetic nanocrystals, MTBs are able to sequester various chemical elements (e.g., carbon and phosphorus) for the biogenesis of intracellular granules, like polyhydroxyalkanoate (PHA) and polyphosphate (polyP), making them potentially important in biogeochemical cycling. Yet, the environmental controls of intracellular storage of carbon and phosphorus in MTB remain poorly understood. Here, we investigated the influence of oxic, anoxic and transient oxic-anoxic conditions on intracellular storage of PHA and polyP in Magnetospirillum magneticum strain AMB-1. In the incubations with oxygen, transmission electron microscopy revealed intercellular granules highly rich in carbon and phosphorus, which were further interpreted as PHA and polyP based on chemical and Energy-Dispersive X-ray spectroscopy analysis. Oxygen had a strong effect on PHA and polyP storage in AMB-1 cells, as PHA and polyP granules accounted for up to 47 ± 23% and 5.1 ± 1.7% of the cytoplasmic space, respectively, during continuous oxic conditions, while granules disappeared in anoxic incubations. Poly 3-hydroxybutyrate (PHB) and poly 3-hydroxyvalerate (PHV) accounted for 0.59 ± 0.66% and 0.0033 ± 0.0088% of dry cell weight, respectively, in anoxic incubations, while the values increased by a factor of 7 and 37 after oxygen was introduced. The results highlight a tight link between oxygen, carbon and phosphorus metabolisms in MTB, where favorable oxic growth conditions can lead to metabolic induction of polyP and PHA granule biogenesis.

Exploring the resilience of constructed wetlands to harmful algal blooms disturbances: A study on microbial response mechanisms

Constructed wetlands (CWs) have emerged as a promising environmentally sustainable technique for wastewater treatment. However, the susceptibility of CWs to disturbances caused by harmful algal blooms (HABs) raises concerns. This study aimed to investigate the impact of HABs on the pollutants' removal performance of CWs and the response of rhizosphere microbial community. Results revealed that CWs possessed an adaptive capacity that enabled them to recover caused by HABs. The rhizosphere was found to stimulate the occurrence of Acinetobacter, which played a critical role to help resist HABs disturbance. This study also observed an increased dissimilatory nitrate reduction metabolic pathway which promoted denitrification and enhanced the nitrogen removal efficiency of CWs. Additionally, the structural equation model further suggested that dissolved oxygen exerted a significant influence on the microbial activities and then affected the pollutants removal performance. Overall, our findings shed light on the mechanism for CW stability maintenance during HABs disturbance.