The responding and ecological contribution of biofilm-leaves of submerged macrophytes on phenanthrene dissipation in sediments

Unraveling the ecological mechanisms of Aluminum on microbial community succession in epiphytic biofilms on Vallisneria natans leaves: Novel insights from microbial interactions

The extensive use of aluminum (Al) poses an escalating ecological risk to aquatic ecosystems. The epiphytic biofilm on submerged plant leaves plays a crucial role in the regulation nutrient cycling and energy flow within aquatic environments. Here, we conducted a mesocosm experiment aimed at elucidating the impact of different Al concentrations (0, 0.6, 1.2, 2.0 mg/L) on microbial communities in epiphytic biofilms on Vallisneria natans. At 1.2 mg/L, the highest biofilms thickness (101.94 µm) was observed. Al treatment at 2.0 mg/L significantly reduced bacterial diversity, while micro-eukaryotic diversity increased. Pseudomonadota and Bacteroidota decreased, whereas Cyanobacteriota increased at 1.2 mg/L and 2.0 mg/L. At 1.2 and 2.0 mg/L. Furthermore, Al at concentrations of 1.2 and 2.0 mg/L enhanced the bacterial network complexity, while micro-eukaryotic networks showed reduced complexity. An increase in positive correlations among microbial co-occurrence patterns from 49.51% (CK) to 57.05% (2.0 mg/L) was indicative of augmented microbial cooperation under Al stress. The shift in keystone taxa with increasing Al concentration pointed to alterations in the functional dynamics of microbial communities. Additionally, Al treatments induced antioxidant responses in V. natans, elevating leaf reactive oxygen species (ROS) content. This study highlights the critical need to control appropriate concentration Al concentrations to preserve microbial diversity, sustain ecological functions, and enhance lake remediation in aquatic ecosystems.

Dissolved organic matter promoted hydroxyl radical formation and phenanthrene attenuation during oxygenation of iron-pillared montmorillonites

The oxygenation of Fe(II)-bearing minerals for hydroxyl radicals (HO•) formation and contaminant attenuation receives increasing attentions. However, information on dissolved organic matter (DOM) with different types, concentrations, and molecular weights (MWs) in manipulating HO• formation and contaminant attenuation during mineral oxygenation remain unclear. In this study, four iron-pillared montmorillonites (IPMs) and two DOM samples [e.g., humic acids (HA) and fulvic acids (FA)] were prepared to explore the HO• formation and phenanthrene attenuation during the oxygenation of IPMs in the presence or absence of DOMs. Results showed that iron-pillared and high-temperature calcination procedures extended the interlayer domain of IPMs, which provided favorable conditions for a high HO• production from 1293 to 14537 μmol kg-1. The surface-absorbed/low crystalline Fe(Ⅱ) was the predominant Fe(Ⅱ) fractionations for HO• production, and presence of DOMs significantly enhanced the HO• production and phenanthrene attenuation. Moreover, regardless of the types and concentrations, the low MW (LMW, <1 kDa) fraction within DOM pool contributed highest to HO• production and phenanthrene attenuation, followed by the bulk and high MW (HMW-, 1 kDa∼0.45 μm) fractions, and FA exhibited more efficient effects in promoting HO• production and phenanthrene attenuation than HA. The fluorescent spectral analysis further revealed that phenolic-like fluorophores in LMW-fraction were the main substances responsible for the enhanced HO• production and phenanthrene attenuation. The results deepen our understandings toward the behaviors and fate of aquatic HO• and contaminants, and also provide technical guidance for the remediation of contaminated environments.

Temporal dynamics of bacterial colonization on five types of microplastics in a freshwater lake

Microplastics (MPs), as a new substrate, provide a unique niche for microbial colonization in the freshwater ecosystems; however, the impacts of long-term MP exposure on colonized bacteria are still unclear. In this study, five MP types were exposed in a freshwater lake for approximately one year, and the MP particles, together with the surrounding water, were collected on days 60, 150, 250 and 330 during the in situ field experiment. Bacteria on the MP surface, as well as free-living bacteria in the surrounding water, were analyzed to evaluate the temporal dynamics of these bacterial communities. Results show that all five MP types exhibited signs of degradation during the exposure process. Additionally, the alpha diversity, community structure and composition of MP-attached bacteria significantly differed from that of the free-living bacteria in the surrounding water, indicating that the five MP types could provide a preferable niche for bacterial colonization in a freshwater environment. Proteobacteria, Chloroflexi, Verrucomicrobiota, Actinobacteriota and Firmicutes were the top five dominant phyla. Some plastic-degrading bacteria included in these phyla were detected, verifying that MP-attached biofilms had a certain degree of MP degradation potential. Some potentially pathogenic bacteria were also detected, suggesting an ecological threat for spreading disease in the aquatic ecosystem. Furthermore, the bacterial community and some metabolic pathways were significantly affected by the MP type (P < 0.01) and exposure time (P < 0.01), indicating that the presence of MPs not only alters the bacterial community structure and composition, but also influences their potential functional properties in freshwater ecosystems. Multiple factors, including the physicochemical properties related to MPs and the environmental parameters of the surrounding water, affect the community composition and the function of MP-attached bacteria to different degrees. Our findings indicate that the presence of MPs has a potential ecological impact on freshwater ecosystems.

Revealing the key species for pyrene degradation in Vallisneria natans rhizosphere sediment via triple chamber rhizome-box experiments

To identify key species associated with pyrene degradation in Vallisneria natans (V.natans) rhizosphere sediment, this work investigated the temporal and spatial changes in the rhizosphere microbial community and the relationship between the changes and the pyrene degradation process through a three-compartment rhizome-box experiment under pyrene stress. The degradation kinetics of pyrene showed that the order of degradation rate was rhizosphere > near-rhizosphere > non-rhizosphere. The difference in the pyrene degradation behavior in the sediments corresponded to the change in the proportions of dominant phyla (Firmicutes and Proteobacteria) and genera (g_Massilia f_Comamonadaceae, g_Sphingomonas). The symbiosis networks and hierarchical clustering analysis indicated that the more important phyla related to the pyrene degradation in the rhizosphere was Proteobacteria, while g_Sphigomonas, f_Comamonadaceae, and especially g_Massilia were the core genera. Among them, f_Comamonadaceae was the genus most affected by rhizosphere effects. These findings strengthened our understanding of the PAHs-degradation microorganisms in V.natans rhizosphere and are of great significance for enhancing phytoremediation on PAHs-contaminated sediment.

Unraveling the ecological mechanisms of bacterial succession in epiphytic biofilms on Vallisneria natans and Hydrilla verticillata during bioremediation of phenanthrene and pyrene polluted wetland

In wetland ecosystem, the microbial succession in epiphytic biofilms of submerged macrophytes remains to be fully elucidated, especially submerged macrophytes used to remediate organic pollutants contaminated sediment. Herein, 16 S rRNA gene sequencing was used to investigate the bacterial dynamics and ecological processes in the biofilms of two typical submerged macrophytes (Vallisneria natans and Hydrilla verticillata) settled in sediment polluted by polycyclic aromatic hydrocarbons (PAHs) at two growth periods. The results presented that the variations of bacterial community in the biofilms were influenced by attached surfaces (explanation ratio: 17.30%), incubation time (32.30%) and environmental factors (39.10%). Bacterial community assembly was mainly driven by dispersal limitation which triggered more positive co-occurrence associations in microbial networks, maintaining ecological stability in the process of bioremediation of PAHs. Additionally, the functional redundancy strength of bacterial community was more affected by attached surface than incubation time. The structural equation model illustrated that community assembly drove β-diversity and explained a part of ecological functions. Environmental factors, community assembly, and β-diversity jointly affected microbial networks. Overall, our study offers new insights into the microbial ecology in biofilms attached on the submerged macrophytes settled in PAH-polluted sediment, providing important information for deeply understanding submerged macrophyte-biofilm complex and promoting sustainable phytoremediation in shallow lacustrine and marshy ecosystems.

Versatile mechanisms and enhanced strategies of pollutants removal mediated by Shewanella oneidensis: A review

The removal of environmental pollutants is important for a sustainable ecosystem and human health. Shewanella oneidensis (S. oneidensis) has diverse electron transfer pathways and can use a variety of contaminants as electron acceptors or electron donors. This paper reviews S. oneidensis's function in removing environmental pollutants, including heavy metals, inorganic non-metallic ions (INMIs), and toxic organic pollutants. S. oneidensis can mineralize o-xylene (OX), phenanthrene (PHE), and pyridine (Py) as electron donors, and also reduce azo dyes, nitro aromatic compounds (NACs), heavy metals, and iodate by extracellular electron transfer (EET). For azo dyes, NACs, Cr(VI), nitrite, nitrate, thiosulfate, and sulfite that can cross the membrane, S. oneidensis transfers electrons to intracellular reductases to catalyze their reduction. However, most organic pollutants cannot be directly degraded by S. oneidensis, but S. oneidensis can remove these pollutants by self-synthesizing catalysts or photocatalysts, constructing bio-photocatalytic systems, driving Fenton reactions, forming microbial consortia, and genetic engineering. However, the industrial-scale application of S. oneidensis is insufficient. Future research on the metabolism of S. oneidensis and interfacial reactions with other materials needs to be deepened, and large-scale reactors should be developed that can be used for practical engineering applications.

Community structure and function of epiphytic bacteria attached to three submerged macrophytes

In aquatic ecosystems, large amounts of epiphytic bacteria living on the leaf surfaces of submerged macrophytes play important roles in affecting plant growth and biogeochemical cycling. The restoration of different submerged macrophytes has been considered an effective measure to improve eutrophic lakes. However, the community ecology of epiphytic bacteria is far from well understood for different submerged macrophytes. In this study, we used quantitative PCR, 16S rRNA gene high-throughput sequencing and functional prediction analysis to explore the structure and function of epiphytic bacteria in an aquatic ecosystem recovered by three submerged macrophytes (Hydrilla verticillata, Vallisneria natans and Potamogeton maackianus) during two growth periods. The results showed that the community compositions and functions of epiphytic bacterial communities on the submerged macrophyte hosts were different from those of the planktonic bacterial communities in the surrounding water. The alpha diversity of the epiphytic bacterial community was significantly higher in October than in July, and the community compositions and functions differed significantly in July and October. Among the three submerged macrophytes, the structures and functions of the epiphytic bacterial community exhibited obvious differences, and some specific taxa were enriched on the biofilms of the three plants. The alpha diversity and the abundance of functions related to nitrogen and phosphorus transformation were higher in the epiphytic bacteria of P. maackianus. In summary, these results provide clues for understanding the distribution and formation mechanisms of epiphytic bacteria on submerged macrophyte leaves and their roles in freshwater ecosystems.

Research trends and hotspots of aquatic biofilms in freshwater environment during the last three decades: a critical review and bibliometric analysis

Freshwater periphytic biofilms (FPBs), existing widely in various aquatic environments, have attracted extensive attention for many years. In the present study, a bibliometric analysis based on Web of Science Core Collection (WoSCC) was used to understand the research progress, trends, and hot topics of FPBs qualitatively and quantitatively. The results indicated that publications on FPBs have increased from 1991 to 2020 rapidly, and researchers have focused more on the areas of environmental sciences, microbiology, and marine freshwater biology. The most influential countries were mainly the USA, Spain, France, and Germany. Cooperation network analysis reflected that the USA and its affiliated institutions played crucial roles in the research of FPB cooperation, but the collaboration between core author groups still fell short. Based on the analysis of top 20 high-cited FPB documents over the last 30 years, research hotspots mainly included micro-observation and assembly mechanisms of FPBs; interactions of FPBs and pollutants including heavy metals, antibiotic resistance genes, pathogens, organic pollutants, and nanoparticles; and the role of FPBs for biogeochemical cycling, especially nitrogen cycling. Additionally, future research directions were proposed. Overall, this study provides a comprehensive and systematic overview of FPBs, which is useful for research development and researchers who are interested in this area.

Removal potential of multiple perfluoroalkyl acids (PFAAs) by submerged macrophytes in aquatic environments: Tolerance of Vallisneria natans and PFAA removal in submerged macrophyte-microbiota systems

Perfluoroalkyl acids (PFAAs) have emerged as a global concern in aquatic environment remediation due to their abundance, persistence, bioaccumulation, and toxicity. To comprehensively understand the removal potential of multiple PFAAs by submerged macrophytes in aquatic environments, systematic investigations into the tolerance of the typical submerged macrophyte Vallisneria natans to 12 typical PFAAs and the removal capacity to PFAAs in V. natans-microbiota systems were carried out. Results showed that although PFAAs could induce the accumulation of hydrogen peroxide and malondialdehyde, V. natans was overall resistant to multiple PFAAs with natural concentrations. Catalase is one of the main strategies of V. natans to alleviate PFAA stress. Microbiota can remove 18.10-30.84% of the PFAAs from the water column. 24.35-73.45% of PFAAs were removed from water in V. natans-microbiota systems. The uptake of plant tissues and the bioaccumulation of microbiota were proposed as the main removal processes. The removal rates were significantly correlated with the perfluorinated carbon atoms numbers (p < 0.05). PFAAs and V. natans increased the relative abundance of Betaproteobacteria, Nostocales, Microscillaceae, Sphingobacteriales, SBR1031, Chlamydiales, Phycisphaerae, Caldilineales, Rhodobacterales, and Verrucomicrobiales. The present study suggested that V. natans can be a potential species to remove multiple PFAAs in aquatic environments, and further providing insights into the PFAAs' remediation.

Temporal changes of microbial community structure and nitrogen cycling processes during the aerobic degradation of phenanthrene

Phenanthrene (PHE) is frequently detected in worldwide soils. But it is still not clear that how the microbial community succession happens and the nitrogen-cycling processes alter during PHE degradation. In this study, the temporal changes of soil microbial community composition and nitrogen-cycling processes during the biodegradation of PHE (12 μg g^-1) were explored. The results showed that the biodegradation of PHE followed the second-order kinetics with a half-life of 7 days. QPCR results demonstrated that the bacteria numbers increased by 67.1%-194.7% with PHE degradation, whereas, no significant change was observed in fungi numbers. Thus, high-throughput sequencing based on 16 S rRNA was conducted and showed that the abundances of Methylotenera, Comamonadaceae, and Nocardioides involved in PHE degradation and denitrification were significantly increased, while those of nitrogen-metabolism-related genera such as Nitrososphaeraceae, Nitrospira, Gemmatimonadacea were decreased in PHE-treated soil. Co-occurrence network analysis suggested that more complex interrelations were constructed, and Proteobacteria instead of Acidobacteriota formed intimate associations with other microbes in responding to PHE exposure. Additionally, the abundances of nifH and narG were significantly up-regulated in PHE-treated soil, while that of amoA especially AOAamoA was down-regulated. Finally, correlation analysis found several potential microbes (Methylotenera, Comamonadaceae, and Agromyces) that could couple PHE degradation and nitrogen transformation. This study confirmed that PHE could alter microbial community structure, change the native bacterial network, and disturb nitrogen-cycling processes.

Removal of perfluoroalkyl acids (PFAAs) in constructed wetlands: Considerable contributions of submerged macrophytes and the microbial community

The broad application of perfluoroalkyl acids (PFAAs) has attracted global concern regarding their adverse environmental effects. The possible removal processes of PFAAs in constructed wetlands were excavated and quantified using two typical submerged macrophytes (rooted Potamogeton wrightii and rootless Ceratophyllum demersum). Our results showed that 33.59-88.99% of PFAAs could be removed via not only sediment sorption or phytoextraction but also by the bioaccumulation of microbiota. The sediment acts as a vital sink for PFAAs, preloading 23.51-50.09% and 16.65-52.18% of PFAAs in treatments with P. wrightii (Pw1) and C. demersum (Cd1), respectively. C. demersum showed a better capacity to accumulate PFAAs (0.91-32.03%) than P. wrightii (<10%). Considerable PFAAs were observed to be distributed in microbes, underlining the non-negligible role of microbiota in bioaccumulating PFAAs. The contributions of planktonic microbes, biofilm microbes, and extracellular polymeric substances in biofilms were 0.39-20.96%, 0.03-7.95%, and 0.39-14.15% in Pw1 and 0.23-15.68%, 0.01-15.68%, and 0.53-26.77% in Cd1, respectively. The adsorption/uptake was significantly correlated with the perfluoroalkyl chain length (p<0.05), except for the uptake of biofilms in C. demersum. Furthermore, PFAAs and submerged macrophytes could decrease the richness of microbiota but increase the relative abundance of some strains in Betaproteobacteriales, Sphingomonadales, and Cytophagales. Our results were helpful for understanding the removal processes of PFAAs in constructed wetlands and their linkages with PFAA properties, thus further providing insight into the management and removal of emerging organic contaminants.

Mutual promotion of submerged macrophytes and biofilms on artificial macrophytes for nitrogen and COD removal improvement in eutrophic water

Both submerged macrophytes (SMs) and artificial macrophytes (AMs) have been widely used to improve water quality in eutrophic water. However, in heavily eutrophic aquatic ecosystems, the purification function of SMs is often restricted by the poor growth state due to competition from algae, while the purification function of AMs is often restricted by the limited carbon source supply for biofilm microbes attached to the AM surface. The objective of this study was to develop a new strategy to increase pollutant removal efficiency (RE) by combining the use of SMs and AMs. Pilot-scale microcosms, including treatments with both SMs and AMs (S&A), only SMs (SO) and only AMs (AO), were established to identify the performance of the new strategy. The results suggest that treatment S&A obtained REs of 88.9% for total nitrogen (TN) and 48.1% for chemical oxygen demand (COD); as comparison, treatments SO and AO obtained REs of 77.4% and 81.2% for TN and REs of -13.7% and 39.0% for COD, respectively. Compared with SO, the S&A treatment benefited SM growth in biomass, leaf chlorophyll concentration and root activity by inhibiting algae growth. In addition, compared with treatment AO, S&A increased the biofilm microbial biomass and the relative abundance of nitrifiers of families Nitrosomonadaceae and Nitrospira attached to AM surfaces. Therefore, by the mutual promotion of SMs and biofilms on AMs, the synergic application of SMs and AMs is a useful strategy for improving TN and COD REs in eutrophic water bodies such as rivers and constructed wetlands. A strategy was developed to increase nitrogen and COD removal in eutrophic water by the mutual promotion of submerged macrophytes and biofilms on artificial macrophytes.

Effects of hydrophyte decomposition on the binding mechanism between fluorescent DOM and copper

Hydrophyte decomposition caused large amounts of dissolved organic matter (DOM) to enter aquatic environment that influence the migration and transformation of heavy metals (HMs). Six hydrophytes with five dry weight gradients (DWG) were used for the decomposition experiments. The results showed that protein-like materials occupy relatively high content in the hydrophyte-derived DOM. The binding properties of DOM-Cu(II) have been explored by using two-dimensional correlation spectroscopy (2D-COS) in conjunction with synchronous fluorescence spectroscopy (SFS) and log-transformed SFS. The weak signals of binding site can be amplified by the log-transformed 2D-COS analysis. Herein, more binding sites can be identified by the log-transformed 2D-COS analysis. The results reveal that tryptophan-like materials show a preferential sequence of binding Cu(II) in the hydrophyte-derived DOM with a relatively low DWG and sediment DOM, and fulvic-like substances indicate a preferential sequence of binding Cu(II) in the hydrophyte-derived DOM with a relatively high DWG. Meanwhile, the results of binding parameters indicate that the log K is the range of 3.61-4.25, 4.33-4.74, 4.59-4.97, 3.91-4.41, and 4.14-4.78 for D1-D5, respectively, suggesting that hydrophyte decomposition can change the binding affinity between DOM components and Cu(II). The complexes of fluorescent components with Cu(II) showed a high log K value at long wavelength (e.g. humic-like substances), and a relatively low fluorescent ligand proportion (f%) at shorter wavelength in the hydrophyte-derived DOM. However, the log K is the range of 3.08-4.31, 4.09-4.45, 3.93-4.35, 4.39-4.75, and 3.95-4.36 for C1-C5, separately. Protein-like substances with Cu(II) showed a relatively high log K value with the exception of C4. The log-transformed 2D-COS can be an analytical tool to understand the binding heterogeneity of DOM with HMs. The study can provide a guide for managing and controlling the effects of hydrophyte decomposition.

Effect of C/N substrates for enhanced extracellular polymeric substances (EPS) production and Poly Cyclic Aromatic Hydrocarbons (PAHs) degradation

Extracellular Polymeric Substances (EPS) influenced Poly Cyclic Aromatic Hydrocarbons (PAHs) degrading Klebsiella pneumoniae was isolated from the marine environment. To increase the EPS production by Klebsiella pneumoniae, several physicochemical parameters were tweaked such as different carbon sources (arabinose, glucose, glycerol, lactose, lactic acid, mannitol, sodium acetate, starch, and sucrose at 20 g/L), nitrogen sources (ammonium chloride, ammonium sulphate, glycine, potassium nitrate, protease peptone and urea at 2 g/L), different pH, carbon/nitrogen ratio, temperature, and salt concentration were examined. Maximum EPS growth and biodegradation of Anthracene (74.31%), Acenaphthene (67.28%), Fluorene (62.48%), Naphthalene (57.84%), and mixed PAHs (55.85%) were obtained using optimized conditions such as glucose (10 g/L) as carbon source, potassium nitrate (2 g/L) as the nitrogen source at pH 8, growth temperature of 37 °C, 3% NaCl concentration and 72 h incubation period. The Klebsiella pneumoniae biofilm architecture was studied by confocal laser scanning microscopy (CLSM) and scanning electron microscope (SEM). The present study demonstrates the EPS influenced PAHs degradation of Klebsiella pneumoniae.

Biofilms attached to Myriophyllum spicatum play a dominant role in nitrogen removal in constructed wetland mesocosms with submersed macrophytes: Evidence from 15N tracking, nitrogen budgets and metagenomics analyses

The mechanisms behind nitrogen removal by the submersed macrophyte-biofilm complex in wetlands remain to be fully elucidated. This study investigated the role of Myriophyllum spicatum and the biofilm on their leaves in nitrogen removal in mesocosm experiments. ¹⁵N tracking showed that 61.9% and 30% of the ¹⁵N, respectively, was removed from the system and assimilated by the macrophyte-biofilm complex after loading with 5.4 mg L^-115N labelled NH₄⁺ for 17 days. Nitrogen budget results showed that about 0.2%, 0.2% and 3.6% of the nitrogen were emitted as water-, HCl- and NaOH-soluble nitrogen-gas species, respectively. Bacteria (76.7-91.8%) were the predominant domain in all samples, followed by eukaryotes (8.0-23.0%), archaea and viruses. Network analyses showed that there were positive- and negative-correlative relationships among nitrogen-cycling genes and nitrifiers and denitrifiers. Our data highlight the important role of biofilm on submersed macrophytes for nitrogen removal.