Unravelling biosynthesis and biodegradation potentials of microbial dark matters in hypersaline lakes.

Biosynthesis and biodegradation of microorganisms critically underpin the development of biotechnology, new drugs and therapies, and environmental remediation. However, most uncultured microbial species along with their metabolic capacities in extreme environments, remain obscured. Here we unravel the metabolic potential of microbial dark matters (MDMs) in four deep-inland hypersaline lakes in Xinjiang, China. Utilizing metagenomic binning, we uncovered a rich diversity of 3030 metagenome-assembled genomes (MAGs) across 82 phyla, revealing a substantial portion, 2363 MAGs, as previously unclassified at the genus level. These unknown MAGs displayed unique distribution patterns across different lakes, indicating a strong correlation with varied physicochemical conditions. Our analysis revealed an extensive array of 9635 biosynthesis gene clusters (BGCs), with a remarkable 9403 being novel, suggesting untapped biotechnological potential. Notably, some MAGs from potentially new phyla exhibited a high density of these BGCs. Beyond biosynthesis, our study also identified novel biodegradation pathways, including dehalogenation, anaerobic ammonium oxidation (Anammox), and degradation of polycyclic aromatic hydrocarbons (PAHs) and plastics, in previously unknown microbial clades. These findings significantly enrich our understanding of biosynthesis and biodegradation processes and open new avenues for biotechnological innovation, emphasizing the untapped potential of microbial diversity in hypersaline environments.

BASALT refines binning from metagenomic data and increases resolution of genome-resolved metagenomic analysis.

Metagenomic binning is an essential technique for genome-resolved characterization of uncultured microorganisms in various ecosystems but hampered by the low efficiency of binning tools in adequately recovering metagenome-assembled genomes (MAGs). Here, we introduce BASALT (Binning Across a Series of Assemblies Toolkit) for binning and refinement of short- and long-read sequencing data. BASALT employs multiple binners with multiple thresholds to produce initial bins, then utilizes neural networks to identify core sequences to remove redundant bins and refine non-redundant bins. Using the same assemblies generated from Critical Assessment of Metagenome Interpretation (CAMI) datasets, BASALT produces up to twice as many MAGs as VAMB, DASTool, or metaWRAP. Processing assemblies from a lake sediment dataset, BASALT produces ~30% more MAGs than metaWRAP, including 21 unique class-level prokaryotic lineages. Functional annotations reveal that BASALT can retrieve 47.6% more non-redundant opening-reading frames than metaWRAP. These results highlight the robust handling of metagenomic sequencing data of BASALT.

Effect of hydraulic regime on sulfur-packed bed performance: Denitrification and disproportionation.

Sulfur-packed beds (SPBs) have been increasingly incorporated into constructed wetland systems to overcome limitations in achieving satisfactory nitrate removal efficiency. However, the underlying impact of hydraulic regimes on SPB performance remains understudied. This study investigated the performance of a pilot-scale SPB, encompassing sulfur autotrophic denitrification (SAD) and sulfur disproportionation (SDP) processes, under various horizontal flow (HF) and vertical flow (VF) regimes. The HF regime exhibited superior SAD efficiency, achieving 3.1-4.4 mg-N/L of nitrate removal compared to 0.9-2.8 mg-N/L under VF regimes. However, greater sulfide production of 3.8-5.6 mg/L was observed, in contrast to only 1.5-2.3 mg/L under VF regimes when SDP occurred. Employing current computational fluid dynamics simulations could predict general regimes but lacked precision in detailing sulfur layer dynamics. In contrast, determining the spatial distribution of SAD substrates and SDP products offered a viable solution, revealing stagnate, short-circuit, and back flows. Moreover, the feasibility of an aeration approach to reduce sulfide emissions below 0.5 mg/L in case of accidental SDP occurrence was confirmed. This study offers a method for assessing detailed hydraulic regimes within SPBs. Additionally, it provides guidance on optimizing the packing of sulfur-based materials when implementing SPBs in constructed wetland systems and presents a strategy for mitigating excessive sulfide emissions.

Synergistic interactions between anammox and dissimilatory nitrate reducing bacteria sustains reactor performance across variable nitrogen loading ratios.

Anaerobic ammonium oxidizing (anammox) bacteria are utilized for high efficiency nitrogen removal from nitrogen-laden sidestreams in wastewater treatment plants. The anammox bacteria form a variety of competitive and mutualistic interactions with heterotrophic bacteria that often employ denitrification or dissimilatory nitrate reduction to ammonium (DNRA) for energy generation. These interactions can be heavily influenced by the influent ratio of ammonium to nitrite, NH4+:NO2-, where deviations from the widely acknowledged stoichiometric ratio (1:1.32) have been demonstrated to have deleterious effects on anammox efficiency. Thus, it is important to understand how variable NH4+:NO2- ratios impact the microbial ecology of anammox reactors. We observed the response of the microbial community in a lab scale anammox membrane bioreactor (MBR) to changes in the influent NH4+:NO2- ratio using both 16S rRNA gene and shotgun metagenomic sequencing. Ammonium removal efficiency decreased from 99.77 ± 0.04% when the ratio was 1:1.32 (prior to day 89) to 90.85 ± 0.29% when the ratio was decreased to 1:1.1 (day 89-202) and 90.14 ± 0.09% when the ratio was changed to 1:1.13 (day 169-200). Over this same timespan, the overall nitrogen removal efficiency (NRE) remained relatively unchanged (85.26 ± 0.01% from day 0-89, compared to 85.49 ± 0.01% from day 89-169, and 83.04 ± 0.01% from day 169-200). When the ratio was slightly increased to 1:1.17-1:1.2 (day 202-253), the ammonium removal efficiency increased to 97.28 ± 0.45% and the NRE increased to 88.21 ± 0.01%. Analysis of 16 S rRNA gene sequences demonstrated increased relative abundance of taxa belonging to Bacteroidetes, Chloroflexi, and Ignavibacteriae over the course of the experiment. The relative abundance of Planctomycetes, the phylum to which anammox bacteria belong, decreased from 77.19% at the beginning of the experiment to 12.24% by the end of the experiment. Analysis of metagenome assembled genomes (MAGs) indicated increased abundance of bacteria with nrfAH genes used for DNRA after the introduction of lower influent NH4+:NO2- ratios. The high relative abundance of DNRA bacteria coinciding with sustained bioreactor performance indicates a mutualistic relationship between the anammox and DNRA bacteria. Understanding these interactions could support more robust bioreactor operation at variable nitrogen loading ratios.

The impact of perfluorooctanoic acid shock on hydrogen-driven nitrate and arsenate removal.

Perfluorooctanoic acid (PFOA) is a type of toxic per- and poly-fluoroalkyl substance (PFAS) commonly found in groundwater due to its use in firefighting and industrial applications. The main purpose of this study was to investigate the influence of PFOA shock on the biological performance of a hydrogen-driven bioreactor for nitrate and arsenate removal. Four hydrogen-driven removal reactors (HdBRs) used for the simultaneous removal of nitrate and arsenal were operated with concentrations of either 0, 1, 5, and 10 mg/L of PFOA to induce shock on the systems and examine the corresponding bacterial response. Our results showed that PFOA shock inhibited and decreased the maximum hydrogen-driven arsenate removal rate. Principal Component Analysis (PCA) confirmed that this performance decrease occurred due to a bacterial strike triggered by PFOA shock. PFOA toxicity also led to protein secretion and sludge density decreases. Bacterial analyses showed shifts in the community population due to PFOA shock. The dominant bacteria phylum Proteobacteria became more abundant, from 41.24% originally to 48.29% after exposure to 10 mg/L of PFOA. Other phyla, such as Euryarchaeota and Bacteroidetes, were more tolerant to PFOA shock. Although some of the predominant species within the sludge of each HdBR exhibited a decline, other species with similar functions persisted and assumed the functional responsibilities previously held by the dominant species.

Managing microbial sulfur disproportionation for optimal sulfur autotrophic denitrification in a pilot-scale elemental sulfur packed-bed bioreactor.

Elemental sulfur packed-bed (S0PB) bioreactors for autotrophic denitrification have gained more attention in wastewater treatment due to their organic carbon-free operation, low operating cost, and minimal carbon emissions. However, the rapid development of microbial S0-disproportionation (MS0D) in S0PB reactor during deep denitrification poses a significant drawback to this new technology. MS0D, the process in which sulfur is used as both an electron donor and acceptor by bacteria, plays a crucial role in the microbial-driven sulfur cycle but remains poorly understood in wastewater treatment setups. In this study, we induced MS0D in a pilot-scale S0PB reactor capable of denitrifying over 1000 m3/d nitrate-containing wastewater. Initially, the S0PB reactor stably removed 6.6 mg-NO3--N/L nitrate at an empty bed contact time (EBCT) of 20 mins, which was designated the S0-denitrification stage. To induce MS0D, we reduced the influent nitrate concentrations to allow deep nitrate removal, resulted in the production of large quantities of sulfate and sulfide (SO42-:S2- 3.2 w/w). Meanwhile, other sulfur-heterologous electron acceptors (SHEAs), e.g., nitrite and DO, were also kept at trace levels. The negative correlations between the SHEAs concentrations and the sulfide productions indicated that the absence of SHEAs was a primary inducing factor to MS0D. The microbial community drastically diverged in response to the depletion of SHEAs during the switch from S0-denitrification to S0-disproportionation. An evident enrichment of sulfur-disproportionating bacteria (SDBs) was found at the S0-disproportionation stage, accompanied by the decline of sulfur-oxidizing bacteria (SOBs). In the end, we discovered that shortening the EBCT and increasing the reflux ratio could inhibit sulfide production by reducing it from 43.9 mg/L to 3.2 mg/L or 25.5 mg/L. In conclusion, our study highlights the importance of considering MS0D when designing and optimizing S0PB reactors for sustainable autotrophic sulfur denitrification in real-life applications.

Dissimilatory sulfate reduction in an anaerobic biofilm reactor for tofu processing wastewater treatment: Bacterial community and their functional genes.

Dissimilatory sulfate reduction (DSR) is the key sulfur cycle that transforms sulfate to sulfide. This process leads to odour issues in wastewater treatment. However, few studies have focused on DSR during treating food processing wastewater with high sulfate. This study investigated DSR microbial population and functional genes in an anaerobic biofilm reactor (ABR) treating tofu processing wastewater. The tofu processing wastewater is a common food processing wastewater in Asia. The full-scale ABR was operated for over 120 days in a tofu and tofu-related products manufacturing factory. Mass balance calculations based on the reactor performance indicated that 79.6-85.1 % of the sulfate was transformed into sulfide irrelevant to dissolved oxygen supplementation. Metagenomic analysis revealed 21 metagenome-assembled genomes (MAGs) containing enzymes encoding DSR. The biofilm contained the complete functional genes of DSR pathway in the full-scale ABR, indicating that biofilm could process DSR independently. Comamonadaceae, Thiobacillus, Nitrosomonadales, Desulfatirhabdium butyrativorans, Desulfomonile tiedjei were the dominant DSR species in the ABR biofilm community. Dissolved oxygen supplementation directly inhibited DSR and mitigated HS- production. It was also found that Thiobacillus contained all the function genes encoding every necessary enzyme in DSR, and thus Thiobacillus distribution directly correlated to DSR and the ABR performance.

Double-edged sword effects of dissimilatory nitrate reduction to ammonium (DNRA) bacteria on anammox bacteria performance in an MBR reactor.

Dissimilatory nitrate reduction to ammonium (DNRA) bacteria imposing double-edged sword effects on anammox bacteria were investigated in an anammox-membrane bioreactor (MBR) experiencing an induced crash-recovery event. During the experiment, the anammox-MBR was loaded with NH4+-N:NO2--N ratios (RatioNH4+-N: NO2--N) of 1.20-1.60. Initially, the anammox-MBR removed over 95% of 100 mg/L NH4+-N and 132 mg/L NO2--N (RatioNH4+-N: NO2--N = 0.76, the well accepted stoichiometric RatioNH4+-N: NO2--N for anammox) in the influent (Stage 0). Then, we induced a system crash-recovery event via nitrite shock loadings to better understand responses from different guilds of bacteria in anammox-MBR, loaded with 1.60 RatioNH4+-N: NO2--N with 100 mg/L NO2--N in the influent (Stage 1). Interestingly, the nitrogen removal by anammox bacteria was maintained for about 20 days before starting to decrease significantly. In Stage 2, we further increased influent nitrite concentration to 120 mg/L (1.33 RatioNH4+-N: NO2--N) to simulate a high nitrite toxicity scenario for a short period of time. As expected, nitrogen removal efficiency dropped to only 16.8%. After the induced system crash, anammox-MBR performance recovered steadily to 93.2% nitrogen removal with a 1.25 RatioNH4+-N:NO2--N and a low nitrite influent concentration of 80 mg/L NO2--N. Metagenomics analysis revealed that a probable causality of the decreasing nitrogen removal efficiency in Stage 1 was the overgrowth of DNRA-capable bacteria. The results showed that the members within the Ignavibacteriales order (21.7%) out competed anammox bacteria (17.0%) in the anammox-MBR with elevated nitrite concentrations in the effluent. High NO2--N loading (120 mg N/L) further caused the predominant Candidatus Kuenenia spp. were replaced by Candidatus Brocadia spp. Therefore, it was evident that DNRA bacteria posed negative effects on anammox with 1.60 RatioNH4+-N: NO2--N. Also, when 120 mg/L NO2--N fed to anammox-MBR (RatioNH4+-N: NO2--N = 1.33), canonical denitrification became the primary nitrogen sink with both DNRA and anammox activities decreased. They probably fed on lysed microbial cells of anammox and DNRA. In Stage 3, a low RatioNH4+-N: NO2--N (1.25) with 80 mg/L NO2--N was used to rescue the system, which effectively promoted DNRA-capable bacteria growth. Although anammox bacteria's abundance was only 7.7% during this stage, they could be responsible for about 90% of the total nitrogen removal during this stage.

Identification of dissimilatory nitrate reduction to ammonium (DNRA) and denitrification in the dynamic cake layer of a full-scale anoixc dynamic membrane bioreactor for treating hotel laundry wastewater.

Identification of dissimilatory nitrate reduction to ammonium (DNRA) and denitrification in the dynamic cake layer of a full-scale anoixc dynamic membrane bioreactor (AnDMBR) for treating hotel laundry wastewater was studied. A series of experiments were conducted to understand the contributions of DNRA and canonical denitrification activities in the dynamic cake layer of the AnDMBR. The dynamic cake layer developed included two phases - a steady transmembrane pressure (TMP) increase at 0.24 kPa/day followed by a sharp TMP jump at 1.26 kPa/day four to five days after the AnDMBR start-up. The nitrogen mass balance results showed that canonical denitrification was predominant during the development of the dynamic cake layer. However, DNRA activity and accumulation of bacteria equipped with a complete DNRA pathway showed a positive correlation to the development of the dynamic cake layer. Our metagenomic analysis identified an approximately 18% of the dynamic cake layer bacterial community has a complete DNRA pathway. Pannonibacter (1%), Thauera (0.8%) and Pseudomonas (3%) contained all genes encoding for funcional enzymes of both DNRA (nitrate reductase and DNRA nitrite reductase) and denitrification (nitrate reductase, nitrous oxide reductase and nitric oxide reductase). No other metagenome-assembled genomes (MAGs) possessed a complete cononical denitrification pathway, indicating food-chain-like interactions of denitrifiers in the dynamic cake layer. We found that COD loading rate could be used to control DNRA and canonical denitrification activities during the dynamic cake layer formation.

Biotransformation of 6:2 Fluorotelomer Thioether Amido Sulfonate in Aqueous Film-Forming Foams under Nitrate-Reducing Conditions.

Despite the prevalence of nitrate reduction in groundwater, the biotransformation of per- and polyfluoroalkyl substances (PFAS) under nitrate-reducing conditions remains mostly unknown compared with aerobic or strong reducing conditions. We constructed microcosms under nitrate-reducing conditions to simulate the biotransformation occurring at groundwater sites impacted by aqueous film-forming foams (AFFFs). We investigated the biotransformation of 6:2 fluorotelomer thioether amido sulfonate (6:2 FtTAoS), a principal PFAS constituent of several AFFF formulations using both quantitative liquid chromatography-tandem mass spectrometry (LC-MS/MS) and qualitative high-resolution mass spectrometry analyses. Our results reveal that the biotransformation rates of 6:2 FtTAoS under nitrate-reducing conditions were about 10 times slower than under aerobic conditions, but about 2.7 times faster than under sulfate-reducing conditions. Although minimal production of 6:2 fluorotelomer sulfonate and the terminal perfluoroalkyl carboxylate, perfluorohexanoate was observed, fluorotelomer thioether and sulfinyl compounds were identified in the aqueous samples. Evidence for the formation of volatile PFAS was obtained by mass balance analysis using the total oxidizable precursor assay and detection of 6:2 fluorotelomer thiol by gas chromatography-mass spectrometry. Our results underscore the complexity of PFAS biotransformation and the interactions between redox conditions and microbial biotransformation activities, contributing to the better elucidation of PFAS environmental fate and impact.

Core carbon fixation pathways associated with cake layer development in an anoxic-oxic biofilm-membrane bioreactor treating textile wastewater.

Microbial carbon fixation pathways have not yet been adequately understood for their role in membrane case layer formation processes. Carbon fixation bacteria can play critical roles in either causing or enhancing cake layer formation in some autotrophic-prone anoxic conditions, such as sulfur-cycling conditions. Understanding the microbes capable of carbon fixation can potentially guide the design of membrane biofouling mitigation strategies in scientific ways. Thus, we used meta-omics methods to query carbon fixation pathways in the cake layers of a full-scale anoxic-oxic biofilm-MBR system treating textile wastewater in this study. Based on the wastewater constituents and other properties, such as anoxic conditions, sulfide-reducing and sulfur-oxidizing bacteria could co-exist in the membrane unit. In addition, low-light radiation conditions could also happen to the membrane unit. However, we could not quantify the light intensity or total energy input accurately because the whole experimental setup was a full-scale system. Potentially complete carbon fixation pathways in the cake layer included the Calvin-Benson-Bassham cycle, Wood-Ljungdahl pathway, and the 3-hydroxypropionate bicycle. We discovered that using aeration could effectively inhibit carbon fixation, which resulted in mitigating membrane cake layer development. However, the aeration resulted in the 3-hydroxypropionate bicycle pathway, presumably used by aerobic sulfur-oxidizing prokaryotes, to become a more abundant carbon fixation pathway in the cake layer under aerobic conditions.

Dissimilatory sulfate reduction in the cake layer of a full-scale anaerobic dynamic membrane bioreactor for hotel laundry wastewater treatment: Bacterial community and functional genes.

Dissimilatory sulfate reduction (DSR) in cake layer of full-scale anaerobic dynamic membrane bioreactor for treating hotel laundry wastewater was studied. Change (Δ) of sulfate concentration (ΔSO42-) was positively correlated to dynamic cake layer (DCL) development, while ΔS2- was negatively correlated. ΔSO32- and ΔSorganic sulfur remained around 1.5-2.5 and 1.2-2.3 mg-S/L, respectively. Thus, DSR was the predominant sulfate reduction process in DCL. 33 binned genomes from DCL microbiome samples possessed one or more DSR functional genes. But only four binned genomes possess all functional genes, and thus can achieve complete DSR. However, no significant variations of these DSR bacteria was obseared during DCL development. Metagenomic analysis predicted that sulfate reduction in DCL was mainly carried out by collaborations between bacteria with incomplete DSR pathways. Among which, sulfite â†’ sulfide by dissimilatory-sulfite-reductase expression bacteria was the key process. Overall results suggested that controlling dissimilatory-sulfite-reductase activities could prevent sulfide buildup in the effluent.

Assessing effects of Ca2+ addition on membrane bioreactor performance and macro-floc sludge characteristics.

Calcium ions (Ca2+) can trigger coagulation-flocculation process to form macro-flocculated sludge (MFS). Thus, dosing Ca2+-containing reagents into membrane bioreactors (MBRs) is considered as a promising approach to mitigate membrane biofouling. However, a mechanistic understanding of Ca2+ addition to MBR performance remains elucidated, such as physicochemical characteristics of MFS and their functionality variations. Consequently, this study was sought to understand the interplays of Ca2+ addition and MBR performance with a focus on characterizing MFS in detail. Three parallel MBRs were amended with 82, 208 and 410 mg-Ca2+/L final concentrations. Particle size analyses revealed that MFS formation was overall enhanced by the Ca2+ addition and granular sludge with diameters of up to 900 µm was formed in the 410 mg-Ca2+/L scenario. We believed that cationic bridges facilitated by elevated Ca2+ concentrations in conjunction with coagulation-flocculation were primary mechanisms of the formation of large flocs. Moreover, significant portions of soluble proteins and polysaccharides were flocculated and precipitated by Ca2+, which demonstrated a negative correlation between extracellular polymeric substances (EPS) concentrations and the formation of MFS. Furthermore, the population abundancies of Thiotrichaceae, Sphingomonadales and Hyphomicrobiaceae decreased in the sludge with Ca2+ addition resulted in profound changes of the microbial communities in the MBRs. But MBR performance, such as chemical oxygen demand removal (over 90%), showed no variation during the MBR operation. On the contrary, total nitrogen removal was inhibited in the MBRs. It was because the enlarging MFS formed diffusion barriers to prevent organic component from entering into the sludge flocs to be consumed.

The Responses to Long-Term Water Addition of Soil Bacterial, Archaeal, and Fungal Communities in A Desert Ecosystem.

The response of microbial communities to continual and prolonged water exposure provides useful insight when facing global climate changes that cause increased and uneven precipitation and extreme rainfall events. In this study, we investigated an in situ manipulative experiment with four levels of water exposure (ambient precipitation +0%, +25%, +50%, and +100% of local annual mean precipitation) in a desert ecosystem of China. After 9 years of water addition, Illumina sequencing was used to analyze taxonomic compositions of the soil bacterial, archaeal, and fungal communities. The results showed significant increases in microbial biomass carbon (MBC) at higher amended precipitation levels, with the highest values reported at 100% precipitation. Furthermore, an increase in the bacterial species richness was observed along the water addition gradient. In addition, the relative abundance of several bacterial phyla, such as Proteobacteria, significantly increased, whereas that of some drought-tolerant taxa, including Actinobacteria, Firmicutes, and Bacteroidetes, decreased. In addition, the phyla Planctomycetes and Nitrospirae, associated with nitrification, positively responded to increased precipitation. Archaeal diversity significantly reduced under 100% treatment, with changes in the relative abundance of Thaumarchaeota and Euryarchaeota being the main contributors to shifts in the archaeal community. The fungal community composition was stable in response to water addition. Results from the Mantel test and structural equation models suggested that bacterial and archaeal communities reacted contrastingly to water addition. Bacterial community composition was directly affected by changing soil moisture and temperature, while archaeal community composition was indirectly affected by changing nitrogen availability. These findings highlight the importance of soil moisture and nitrogen in driving microbial responses to long-term precipitation changes in the desert ecosystem.

Development of radio-frequency identification (RFID) sensors suitable for smart-monitoring applications in sewer systems.

Sanitary and stormwater sewers are buried assets that play important roles in the prevention of diseases and the reduction of health risks for our societies. Due to their hidden nature, these assets are not frequently assessed and maintained to optimal conditions. The lack of maintenance can cause sewer blockages and overflows that result in the release of pathogens into the environment. For cities, monitoring sewer conditions on a large-scale can be costly, time-consuming, and labor-intensive if using current low-throughput technologies, such as dye testing or closed-circuit television. Alternatively, smart sensor systems can provide low-cost, high-throughput, and automatic data-driven features for real-time monitoring applications. In this study, we developed ultrahigh-frequency radio-frequency identification (UHF RFID)-based sensors that are flushable and suitable for sanitary and stormwater pipes quick surveys. 3D printed RFID sensors were designed to float at the water-air interface and minimize the water interference to RF signal communications. The optimal detection range was also determined to support the design and installation of the reader in various utility holes. Field trials demonstrated that the UHF RFID system is a low-cost, high-throughput, and robust solution for monitoring blockage, illicit-connection, and water flow in sewer networks.

Challenges in biodegradation of non-degradable thermoplastic waste: From environmental impact to operational readiness.

Non-degradable plastics such as polyethylene (PE), polypropylene (PP), polystyrene (PS), and polyethylene terephthalate (PET) are among the most generated plastic wastes in municipal and industrial waste streams. The mismanagement of abandoned plastics and toxic plastic additives have threatened marine and land fauna as well as human beings for several decades. The available thermal processes can degrade plastic at pilot- and commercial-scale. However, they are energy-intensive and can generate toxic gases. Degradation of plastic waste with the help of live microorganisms (biodegradation) is an eco- and environmentally friendly method for plastic degradation, although the slow processing time and low degradation rate still hinder its applications at pilot- and large-scale. In this review, the advantages and limitations of current plastic degradation methods, their technology readiness levels (TRL), biodegradation mechanisms and the associated challenges in biodegradation are assessed in detail. Based on this analysis, a path toward an efficient and greener way toward degradation of non-recyclable single-use PE, PP, PS and PET plastic is proposed.

Assimilatory and dissimilatory sulfate reduction in the bacterial diversity of biofoulant from a full-scale biofilm-membrane bioreactor for textile wastewater treatment.

Assimilatory and dissimilatory sulfate reduction (ASR and DSR) are the core bacterial sulfate-reducing pathways involved in wastewater treatment. It has been reported that sulfate-reducing activities could happen within biofoulants of membrane bioreactors during wastewater treatment. Biofoulants are mainly microbial products contributing membrane fouling and subsequent rising energy consumption in driving membrane filtration. Biofoulants from a full-scale biofilm-membrane bioreactor (biofilm-MBR) treating textile wastewater were investigated in this study. During a 10-month operation, sulfate concentrations in the effluent of the biofilm-MBR gradually decreased alongside with the creeping up sulfite concentrations when biofoulants were also building up on membrane modules. Sulfide had no apparent increases in the effluent during this period. Metagenomic analysis revealed diverse microbial communities residing in the biofoulants. Further analysis on their genetic traits revealed abundant ASR's and DSR's functional genes. A plethora of sulfate-reduction bacteria (SRB), including the well-known Desulfovibrio, Desulfainum, Desulfobacca, Desulfobulbus, Desulfococcus, Desulfonema, Desulfosarcina, Desulfobacter, Desulfobacula, Desulfofaba, Desulfotigum, Desulfatibacillum, Desulfatitalea, Desulfobacterium, were detected in the biofoulants. They were believed to play some important carbon and sulfur-cycling roles in our study. Based on metagenomic analysis, we also deduced that ASR was a functionally more important sulfate-reducing route because of the high abundance of assimilatory sulfate reductases detected. Also, the "AMP (adenosine monophosphate)→sulfite" step was a key reaction shared by both ASR and DSR in the biofoulant. This step might be responsible for the sulfite accumulation in the biofilm-MBR effluent. Overall, ASR functional genes in the biofoulants were more abundant. But the bacteria possessing complete DSR pathways caused the sulfide production in the biofilm-MBR.

Core nitrogen cycle of biofoulant in full-scale anoxic & oxic biofilm-membrane bioreactors treating textile wastewater.

Core nitrogen cycle within biofoulant in full-scale anoxic & oxic biofilm-membrane bioreactor (bMBR) treating textile wastewater was investigated. Wastewater filtered through membrane with biofoulant had elevated NH4+-N and NO2--N concentrations corresponding to decreased NO3--N concentrations. Nevertheless, total nitrogen concentrations did not change significantly, indicating negligible nitrogen removal activities within biofoulant. Metagenomic analysis revealed a lack of genes, such as AmoCAB and Hao in biofoulant, indicating absence of nitrification or anammox populations. However, genes encoding complete pathway for dissimilatory nitrate reduction to ammonium (DNRA) were discovered in 15 species that also carry genes encoding both nitrate reductase and nitrite reductase. No specie contained all genes for complete denitrification pathway. High temperature, high C:N ratio, and anoxic conditions of textile wastewater could favorite microbes growth with DNRA pathway over those with canonical denitrification pathway. High dissolved oxygen concentrations could effectively inhibit DNRA to minimize ammonia concentration in the effluent.

Specific Denitrifying and Dissimilatory Nitrate Reduction to Ammonium Bacteria Assisted the Recovery of Anammox Community From Nitrite Inhibition.

The anaerobic ammonium oxidation (anammox) by autotrophic anaerobic ammonia-oxidizing bacteria (AnAOB) is a biological process used to remove reactive nitrogen from wastewater. It has been repeatedly reported that elevated nitrite concentrations can severely inhibit the growth of AnAOB, which renders the anammox process challenging for industrial-scale applications. Both denitrifying (DN) and dissimilatory nitrate reduction to ammonium (DNRA) bacteria can potentially consume excess nitrite in an anammox system to prevent its inhibitory effect on AnAOB. However, metabolic interactions among DN, DNRA, and AnAOB bacteria under elevated nitrite conditions remain to be elucidated at metabolic resolutions. In this study, a laboratory-scale anammox bioreactor was used to conduct an investigation of the microbial shift and functional interactions of AnAOB, DN, and DNRA bacteria during a long-term nitrite inhibition to eventual self-recovery episode. The relative abundance of AnAOB first decreased due to high nitrite concentration, which lowered the system's nitrogen removal efficiency, but then recovered automatically without any external interference. Based on the relative abundance variations of genomes in the inhibition, adaptation, and recovery periods, we found that DN and DNRA bacteria could be divided into three niche groups: type I (types Ia and Ib) that includes mainly DN bacteria and type II and type III that include primarily DNRA bacteria. Type Ia and type II bacteria outcompeted other bacteria in the inhibition and adaptation periods, respectively. They were recognized as potential nitrite scavengers at high nitrite concentrations, contributing to stabilizing the nitrite concentration and the eventual recovery of the anammox system. These findings shed light on the potential engineering solutions to maintain a robust and efficient industrial-scale anammox process.

Degradation of plastic waste using stimulated and naturally occurring microbial strains.

The capability of different strains derived from soil, activated sludge, farm sludge, and worms' excreta were investigated for biodegradation of high-density polyethylene, polystyrene foam, polypropylene and polyethylene terephthalate in unstimulated and stimulated conditions. Biodegradation using naturally occurring microbial strains examined in mixed (270 days) and individual (100 days) systems, while H2O2 stimulated strains were tested only in the mixed system (30 days). Penicillium raperi, Aspergillus flavus, Penicillium glaucoroseum and Pseudomonas sp. were isolated as the most plastic degrading microbes. Maximum weight loss was seen by incubation of polyethylene with Aspergillus flavus (5.5%) in unstimulated mix condition. Fourier Transform Infrared Spectroscopy (FT-IR) revealed formation of new functional groups as hydroxyl, carbonyl, alkene and alkoxy in the treated plastics. Visualisation of plastics by optical, atomic force (AFM) and electron microscopy (SEM) were also illustrated biodegradation. The derived by-products from microbial degradation was tested, and found no inhibition on microbial growth and performance.