Rhizosphere Of Phragmites Australis Research Articles

Mechanism of polycyclic aromatic hydrocarbons degradation in the rhizosphere of Phragmites australis: Organic acid co-metabolism, iron-driven, and microbial response

Microbial co-metabolism is crucial for the efficient biodegradation of polycyclic aromatic hydrocarbons (PAHs); however, their intrinsic mechanisms remain unclear. To explore the co-metabolic degradation of PAHs, root organic acids (ROAs) (phenolic ROAs: caffeic acid [CA] and ferulic acid [FA]; non-phenolic ROAs: oxalic acid [OA]) were exogenously added as co-metabolic substrates under high (HFe) and low (LFe) iron levels in this study. The results demonstrated that more than 90% of PAHs were eliminated from the rhizosphere of Phragmites australis. OA can promote the enrichment of unrelated degrading bacteria and non-specific dioxygenases. FA with a monohydroxy structure can activate hydroxylase; however, it relies on phytosiderophores released by plants (such as OA) to adapt to stress. Therefore, non-specific co-metabolism occurred in these units. The best performance for PAH removal was observed in the HFe–CA unit because: (a) HFe concentrations enriched the Fe-reducing and denitrifying bacteria and promoted the rate-limiting degradation for PAHs as the enzyme cofactor; (b) CA with a dihydroxyl structure enriched the related degrading bacteria, stimulated specific dioxygenase, and activated Fe to concentrate around the rhizosphere simultaneously to perform the specific co-metabolism. Understanding the co-metabolic degradation of PAHs will help improve the efficacy of rhizosphere-mediated remediation.

Characterizing bacterial communities in Phragmites australis rhizosphere and non-rhizosphere sediments under pressure of antibiotics in a shallow lake.

Antibiotics are ubiquitous pollutants and widely found in aquatic ecosystems, which of rhizosphere sediment and rhizosphere bacterial communities had certain correlation. However, the response of bacterial communities in Phragmites australis rhizosphere and non-rhizosphere sediments to antibiotics stress is still poorly understood. To address this knowledge gap, the samples of rhizosphere (R) and non-rhizosphere (NR) sediments of P. australis were collected to investigate the differences of bacterial communities under the influence of antibiotics and key bacterial species and dominate environmental factors in Baiyangdian (BYD) Lake. The results showed that the contents of norfloxacin (NOR), ciprofloxacin (CIP) and total antibiotics in rhizosphere sediments were significantly higher than that in non-rhizosphere sediments, meanwhile, bacterial communities in non-rhizosphere sediments had significantly higher diversity (Sobs, Shannon, Simpsoneven and PD) than those in rhizosphere sediments. Furthermore, total antibiotics and CIP were found to be the most important factors in bacterial diversity. The majority of the phyla in rhizosphere sediments were Firmicutes, Proteobacteria and Campilobacterota, while Proteobacteria, Chloroflexi was the most abundant phyla followed by Bacteroidota, Actinobacteriota in non-rhizosphere sediments. The dominate factors of shaping the bacterial communities in rhizosphere were total antibiotics, pH, sediment organic matter (SOM), and NH4-N, while dissolved organic carbon (DOC), NO3-N, pH, and water contents (WC) in non-rhizosphere sediments. It is suggested that antibiotics may have a substantial effect on bacterial communities in P. australis rhizosphere sediment, which showed potential risk for ARGs selection pressure and dissemination in shallow lake ecosystems.

Alkalibacter rhizosphaerae sp. nov., a CO-utilizing bacterium isolated from tidal flat sediment, and emended description of the genus Alkalibacter.

A novel anaerobic, rod-shaped, non-motile bacterium, designated strain ES005T, was isolated from tidal flat sediments near the rhizosphere of Phragmites australis at Eulsukdo Island, Republic of Korea. A polyphasic approach revealed that cells of the strain were Gram-stain-positive, catalase- and oxidase-negative, non-spore-forming rods. Phylogenetic analyses based on 16S rRNA gene sequences revealed that strain ES005T belonged to the family Eubacteriaceae, class Clostridia and showed the highest sequence similarity to Alkalibacter mobilis (97.52 %) and followed by Alkalibacter saccharofermentans Z-79820T (96.72%). The OrthoANI value between strain ES005T and A. mobilis was 69.67 %. Strain ES005T grew optimally at 33-37 °C, at pH 6.0-7.0 and in the presence of 1-2 % (w/v) NaCl. Growth in 12.5 % CO atmosphere was observed. Acetate and formate were end products of fructose fermentation and growth on CO. The major cellular fatty acids of strain ES005T were C14 : 0 (39.1 %) and C16 : 0 (26.6 %). The major polar lipids were diphoshatidylgycerol, phosphatidylglycerol and three unidentified phospholipids. The DNA G+C content of strain ES005T was 46.9 mol%. Based on the phenotypic, phylogenetic, genomic and chemotaxonomic features of the isloate, strain ES005T represents a novel species, for which the name Alkalibacter rhizosphaerae sp. nov. is proposed. The type strain is ES005T (=KCTC 25246T=JCM 34530T).

Diversity of nirS and nirK denitrifying bacteria in rhizosphere and non-rhizosphere soils of halophytes in Ebinur Lake Wetland

There are few studies on denitrification related to the nitrogen cycle in Ebinur Lake wetland. This study aimed to explore the response of the diversity and composition of denitrifying bacteria to the environmental factors in wetland, so as to obtain more information about the community structure of denitrifying bacteria driven by environmental factors. Using the genes encoding nitrite reductase (nirS and nirK) as molecular markers, we analysed the seasonal changes in the diversity of denitrifying bacteria in halophyte soils by high-throughput sequencing technology. The results showed that the diversity of denitrifying bacteria was higher in July and lower in April, showing seasonal changes. The diversity index of denitrifying bacteria in rhizosphere soil was higher than that in non-rhizosphere soil. The diversity of denitrifying bacteria in the Phragmites australis rhizosphere soil was the highest. The diversity of nirK denitrifying bacteria was higher than that of nirS denitrifying bacteria, but the relative abundance was lower than that of nirS denitrifying bacteria. Three-way ANOVA showed that soil types, vegetation types and season had significant effects on the diversity of denitrifying bacteria. Furthermore, redundancy analysis indicated that nitrate was the environmental factor that significantly affected the community structure of nirS denitrifying bacteria in wetland, and electric conductivity, total nitrogen, ammonium and nitrate were the environmental factors that significantly affected the community structure of nirK denitrifying bacteria. These results provide data basis and theoretical support for the dynamic change of diversity of denitrifying bacteria in wetland.

Removal pathway quantification and co-metabolic mechanism evaluation of alkylphenols from synthetic wastewater by phenolic root exudates in the rhizosphere of Phragmites australis

Phenolic root exudates (PREs) released from wetland plants are potentially effective for accelerating the biodegradation of alkylphenols, yet the inherent behavior is still unclear. In this study, two representative root exudates (REs), namely p-coumaric acid (PREs) and oxalic acid (non-PREs) were exogenously added as specific and non-specific co-metabolic substrates, respectively, to elucidate the quantification of each removal pathway and degradation mechanism of co-metabolism for alkylphenols (i.e. p-tert-butylphenol (PTBP)) from synthetic wastewater. The results showed that soil adsorption (31–37%), microbial degradation (27–37%), and plant uptake (16–41%) are the main removal pathways of PTBP by PREs in the Phragmites australis rhizosphere. Both REs enriched anaerobic functional community (anaerobic ammonium oxidation bacteria and denitrifying bacteria) and promoted the usage of PTBP as carbon source and/or electron donor. The activity of non-specific enzyme (polyphenol oxidase) was enhanced by RE which owning a significant positive correlation with bacterial abundance, whereas only PREs strengthened the activity of specific enzyme (monophenol oxidase) catalyzing the phenolic ring hydroxylation of PTBP followed by a dehydrogenation route. Moreover, exogenous PREs significantly improved the growth of degrading-related bacteria (Sphingomonas and Gemmatimonas), especially in unplanted soils with high activity of dioxygenase catalyzing the cleavage pathway of PTBP, instead of plant presence.

Contrasting Patterns of the Resident and Active Rhizosphere Bacterial Communities of Phragmites Australis.

Rhizosphere microbes play a key role in maintaining plant health and regulating biogeochemical cycles. The active bacterial community (ABC) in rhizosphere, as a small fraction of the rhizosphere resident bacterial community (RBC), has the potential to actively participate in nutrient cycling processes at the root-sediment interface. Here, we investigated the ABC and RBC within the rhizosphere of Phragmites australis (P. australis) subjected to different environmental conditions (i.e., seasons and flooding conditions) in Lake Taihu, China. Our results indicated that RBC exhibited significantly higher alpha diversity as well as lower beta diversity than ABC. The active ratios of 16S rRNA to 16S rDNA (also RNA/DNA) of the bacterial communities in summer and winter suggested a lower proportion of potential active taxa in the rhizosphere bacterial community during summer. Network analysis showed that negative correlations in each network were observed to dominate the species correlations between the rhizosphere and bulk sediment bacterial communities. Our results revealed that niche differentiation and seasonal variation played crucial roles in driving the assembly of ABC and RBC associated with the rhizospheres of P. australis. These findings broaden our knowledge about how rhizosphere bacterial communities respond to environmental variations through changing their diversity and composition.

O2 distribution and dynamics in the rhizosphere of Phragmites australis, and implications for nutrient removal in sediments

Root-triggered microscale variations in O2 distribution in the rhizosphere of young Phragmites australis are important for nutrient removal in sediments. In this study, the micro-scale O2 dynamics and the small-scale changes of soluble reactive phosphorus (SRP) and ammonium (NH4+) in the rhizosphere of P. australis were investigated using planar optodes and high-resolution dialysis (HR-Peeper), respectively. Results suggested that root O2 leakage has a highly variable distribution depending on the stage of root growth, the site of O2 leakage gradually shift from the entire emerging main roots to the main root tip and subsequently shifted the emerging lateral roots. The O2 concentration increased in the rhizosphere with increasing light intensity and O2 levels in the overlying water. Continuous O2 release from the lateral roots causes the formation of iron plaque on the surface of lateral roots, which reduce the mobility of P by adsorption of iron plaque in the rhizosphere. The oscillation of oxic-anoxic root zones improves nitrogen removal through the processes of anammox, heterotrophic denitrification and nitrification. This work from the micro-scale demonstrates that the O2 concentration is the spatio-temporal variations in the rhizosphere, and it presents an important role for nutrient removal in sediments.

Composition and co-occurrence patterns of Phragmites australis rhizosphere bacterial community

High oxygen levels and root exudates together provide a resource-enriched habitat for rhizosphere microbes that, in turn, foster plant growth and perform key ecological functions. Plant genotype is a main factor shaping rhizosphere bacterial communities; however, the influence of plant genotype on the rhizosphere bacterial community of aquatic macrophytes remains unknown. Here we collected samples of the rhizosphere and bulk sediments of two genotypes of the macrophyte Phragmites australis from the littoral areas of freshwater lakes in China. High-throughput sequencing of the 16S rRNA gene was used to characterize the rhizosphere bacterial community. We found that the rhizosphere recruited a distinct bacterial community relative to that of the bulk sediment. The rhizosphere microbial community was characterized by distinct community composition and core OTUs comprising a few dominant taxa involved in the regulation of plant fitness and nutrient cycling. These taxa included Arthrobacter, Pseudomonas, Trichococcus, and Ramlibacter. Network analysis showed distinct co-occurrence patterns and a genotype-specific preference for hub taxa within the rhizosphere bacterial communities of each genotype. Functional analysis revealed difference between the relative abundance of functional groups participating in C, N, and S cycling. Our results improve our understanding of the composition of the rhizosphere bacterial community of aquatic macrophytes and highlight the importance of a comprehensive consideration of plant genotype in plant bioremediation in aquatic ecosystems.

Accelerated biodegradation of p-tert-butylphenol in the Phragmites australis rhizosphere by phenolic root exudates

Phenolic root exudates (PREs) released from plants are potentially effective for the degradation of aromatic compounds, yet the inherent process and mechanism remain insufficiently elucidated. In this study, we selected four representative PREs of P. australis, namely p-hydroxybenzoic acid (PHA), p-coumaric acid (PCA), caffeic acid (CA), and ferulic acid (FA), to investigate the accelerated biodegradation of p-tert-butylphenol (PTBP) by PREs in the rhizosphere and their mechanisms. The results showed that PTBP was initially adsorbed to root surface, and subsequently degraded by rhizosphere microbes of P. australis. The presence of PHA, PCA, and FA was beneficial for the enrichment of PTBP-degrading bacteria and the decomposition of PTBP, particularly PCA. Although CA was also favorable to microbial accumulation, it had no effect on PTBP degradation. This is possibly because PHA, PCA, and FA with monohydroxy structure similar like PTBP may promote the microbes for releasing hydroxylase to catalyze the phenolic ring hydroxylation followed by a cleavage pathway, whereas CA with ortho-dihydroxy structure cannot act on this reaction. Collectively, our data suggest PREs can accelerate biodegradation of specific aromatic compounds (e.g. PTBP) via co-metabolism in the rhizosphere of plants, according to their functional structures.

Intraspecific variation in indirect plant-soil feedbacks influences a wetland plant invasion.

Plant-soil feedbacks (PSFs) influence plant competition via direct interactions with pathogens and mutualists or indirectly via apparent competition/mutualisms (i.e., spillover to co-occurring plants) and soil legacy effects. It is currently unknown how intraspecific variation in PSFs interacts with the environment (e.g., nutrient availability) to influence competition between native and invasive plants. We conducted a fully crossed multi-factor greenhouse experiment to determine the effects of Phragmites australis rhizosphere soil biota, interspecific competition, and nutrient availability on biomass of replicate populations from one native and two invasive lineages of common reed (P.australis) and a single lineage of native smooth cordgrass (Spartina alterniflora). Harmful soil biota consistently dominated PSFs involving all three P.australis lineages, reducing biomass by 10%. Indirect PSFs (i.e., soil biota spillover) from the two invasive P.australis lineages reduced S.alterniflora biomass by 7%, whereas PSFs from the native P.australis lineage increased S.alterniflora biomass by 6%. Interestingly, interspecific competition and PSFs interacted to weaken their respective impacts on S.alterniflora, whereas they exerted synergistic negative effects on P.australis. Phragmitesaustralis soil biota decreased S.alterniflora biomass when grown alone (i.e., a soil legacy), but increased S.alterniflora biomass when grown with P.australis, suggesting that P.australis recruits harmful generalist soil biota or facilitates S.alterniflora via spillover (i.e., apparent mutualism). Soil biota also reduced interspecific competition impacts on S.alterniflora, although it remained competitively inferior to P.australis across all treatments. Competitive interactions and responses to nutrients did not differ among P.australis lineages, indicating that interspecific competition and nutrient deposition may not be key drivers of P.australis invasion in North America. Although soil biota, interspecific competition, and nutrient availability appear to have no direct impact on the success of invasive P.australis lineages in North America, intraspecific lineage variation in indirect spillover and soil legacies from P.australis occur and may have important implications for co-occurring native species and restoration of invaded habitats. Our study integrates multiple factors linked to plant invasions, highlighting that indirect interactions are likely commonplace in influencing plant community dynamics and invasion success and impacts.

Niche partition of phenanthrene-degrading bacteria along a Phragmites australis rhizosphere gradient

The rhizosphere is a critical interface for pollutant remediation in soils. Association between biodegradation of organic pollutants and spatial pattern of degraders along the rhizosphere gradient is, however, still unclear. This study investigated the phenanthrene-degrading bacterial consortia in a Phragmites australis rhizosphere using DNA-stable isotope probing (DNA-SIP). The relative abundance of Sphingomonadales in the 13C-labeled consortia decreased with the distance from roots, suggesting that its contribution in phenanthrene degradation was decreased with the distance from roots. Conversely, the relative abundance of Rhizobiales, Rhodobacterales, Lactobacillales, and Enterobacteriales in 13C-labeled consortia increased with the distance from roots, suggesting that their contributions in phenanthrene degradation were increased with the distance from roots. The linkage numbers of bacterial species in the co-occurrence network increased with the percentages of 13C-labeled reads, suggesting the critical role of syntrophic interactions for phenanthrene degraders. These results suggest the niche partition of phenanthrene degraders, which leaded to the non-linear variation of phenanthrene degradation rates along the rhizosphere gradient. These findings will help us to better understand rhizo degradation of organic pollutants and optimize bioremediation technology by achieving a trade-off among different degraders.

Bacterial community dynamic associated with autochthonous bioaugmentation for enhanced Cu phytoremediation of salt-marsh sediments

Autochthonous bioaugmentation for metal phytoremediation is still little explored, particularly its application to estuarine salt marshes, but results obtained so far are promising. Nevertheless, understanding the behaviour of the microbial communities in the process of bioaugmentation and their role in improving metal phytoremediation is very important to fully validate the application of this biological technology. This study aimed to characterize the bacterial community dynamic associated with the application of autochthonous bioaugmentation in an experimentation which showed that Phragmites australis rhizosphere microorganisms could increase this salt marsh plant potential to phytoremediate Cu contaminated sediments. Bacterial communities present in the autochthonous microbial consortium resistant to Cu added to the medium and in the sediment at the beginning and at the end of the experiment were characterized by ARISA. Complementarily, the consortium and the sediment used for its production were characterized by next generation sequencing using the pyrosequencing platform 454. The microbial consortium resistant to Cu obtained from non-vegetated sediment was dominated by the genus Lactococcus (46%), Raoultella (25%), Bacillus (12%) and Acinetobacter (11%), whereas the one obtained form rhizosediment was dominated by the genus Gluconacetobacter (77%), Bacillus (17%) and Dyella (3%). Results clearly showed that, after two months of experiment, Cu caused a shift in the bacterial community structure of sediments, an effect that was observed either with or without addition of the metal resistant microbial consortium. Therefore, bioaugmentation application improved the process of phytoremediation (metal translocation by the plant was increased) without inducing long term changes in the bacterial community structure of the sediments. So, phytoremediation combined with autochthonous bioaugmentation can be a suitable technology for the recovery of estuarine areas, contributing for an efficient risk management strategy of these coastal zones.

Bacterial communities in the rhizosphere of Phragmites australis from an oil-polluted wetland

ABSTRACTAlthough Phragmites australis is commonly planted in constructed wetlands, very little is known about its roots-associated bacterial communities, especially in wetlands used for the remediation of oil produced waters. Here, we describe the bacterial diversity, using molecular (illumina MiSeq sequencing) and cultivation techniques, in the rhizosphere soils of P. australis from an oil-polluted wetland in Oman. The obtained isolates were tested for their plant-growth promoting properties. Most sequences belonged to Proteobacteria, Bacteriodetes and Firmicutes. Sequences of potential hydrocarbon-degrading bacteria (e.g. Ochrobactrum, and Pseudomonas) were frequently encountered. All soils contained sequences of known sulfur-oxidizing (e.g. Thiobacillus, Thiofaba, Rhodobacter and Sulfurovum) and sulfate-reducing bacteria, although the latter group made up only 0.1% to 3% of total sequences. The obtained isolates from the rhizosphere soils were phylogenetically affiliated to Serratia, Acinetobacter, Xenorhabdus, Escherichia and Salmonella. All strains were able to solubilize phosphate and about half were capable of producing organic acids and 1-aminocyclopropane-1-carboxylate (ACC) deaminase. Around 42% of the strains had the ability to produce indole acetic acid and siderophores. We conclude that the rhizosphere soils of P. australis in oil polluted wetlands harbor diverse bacterial communities that could enhance the wetland performance through hydrocarbon degradation, nutrient cycling and supporting plant growth.

In vitro toxic effects of heavy metals on fungal growth and phosphate-solubilising abilities of isolates obtained from Phragmites australis rhizosphere

ABSTRACT In this research, we evaluated the toxic effect of metal ions on mycelial growth and phosphate-solubilising activity of soil-borne micromycetes isolated from the Phragmites australis rhizosphere using Pikovskaya-agar plates supplemented with four metal concentrations. The diameter growth rate (DGR) decreased as the metal concentration rise for all tested fungi. Trichoderma atroviride had the fastest growth rate (1.48 cm2 day−1) and was the least susceptible to Al3+, Cd2+, Cr3+, Cu2+ and Pb2+ with a median effective concentration (MEC50) of 12.19, 0.48, 4.51, 11.44 and 50.05 mM, respectively. Aspergillus japonicus was the most tolerant to Co2+, Ni2+ and Zn2+, with MEC50 values of 3.36, 1.095 and 2.34 mM, respectively. Penicillium italicum was the most tolerant to Cr6+ (MEC50 = 0.677 mM). The ability to solubilise phosphate remained, despite the decrease in the DGR, and P. italicum and Penicillium dipodomyicola had the highest Phosphate Solubilisation Indexes (PSIs) at 1.97 and 2.12, respectively. In particular, P. italicum recorded the highest PSI of all the studied isolates at 0.62 mM Cr3+ (PSI = 4.74). A. japonicus and T. atroviride were the most tolerant isolates to all tested metals, which suggests that these isolates are promising candidates for further study with regard to mycoremediation and biofertilisation of metal-polluted soils.

Effect of Cd⁺² on phosphate solubilizing abilities and hydrogen peroxide production of soil-borne micromycetes isolated from Phragmites australis-rhizosphere.

The aims of this work were to evaluate the phosphate-solubilization and hydrogen peroxide (H2O2) production by the soil-borne micromycetes, Aspergillus japonicus, Penicillium italicum and Penicillium dipodomyicola, isolated from Phragmites australis rhizosphere and to study the effect of several concentrations of Cadmium (Cd(2+)) on both variables. Our results showed that P. italicum achieved a higher P-solubilization and H2O2 production than A. japonicus and P. dipodomyicola, as only P. italicum showed a positive correlation (R(2) = 0.71) between P-solubilization and H2O2 production. In dose-response assays, P. italicum was also more tolerant to Cd(2+) (0.31 mM) in comparison to A. japonicus (0.26 mM). Analysis of the 2(4) factorial experimental design showed that P-solubilization by P. italicum was negatively affected by increases in Cd(2+) (p = 0.04) and yeast extract (p = 0.02) in the culture medium. The production of H2O2 was positively affected only by glucose (p = 0.002). Fungal biomass production was reduced significantly (p = 0.0009) by Cd(2+) and increased (p = 0.0003) by high glucose concentration in the culture medium. The tolerance and correlation between P-solubilization and H2O2 production in the presence of Cd(2+) was strain and species dependent. The effects of Cd(2+), glucose, ammonium sulfate and yeast extract on those variables were evaluated through a two-level factorial design. P. italicum is promising for P-solubilization in soils contaminated with Cd(2+) and may be an alternative for manufacture of biofertilizers to replace chemical fertilizers.

Assessment of rhizospheric culturable bacteria of Phragmites australis and Juncus effusus from polluted sites.

This study aimed at the isolation and characterization of metal(loid)-tolerant bacteria from the rhizosphere of Phragmites australis and Juncus effusus plants growing in two long-term contaminated sites in Northern Portugal. Site 1 had higher contamination than Site 3. Bacteria were isolated using metal(loid)-supplemented (Cd, Zn, and As) media. Isolates were grouped by random amplified polymorphic DNA and identified by 16S rRNA gene sequencing. Strains were also examined for their metal(loid) tolerance. The counts of metal(loid)-tolerant bacteria were higher in Site 1 and ranged between log 7.17 CFU g(-1) soil in As-containing medium and log 7.57 CFU g(-1) soil in Zn-containing medium, while counts at Site 3 varied between log 5.33 CFU g(-1) soil in Cd-containing medium and log 6.97 CFU g(-1) soil in As-containing medium. The composition of bacterial populations varied between locations. In Site 1, the classes Actinobacteria (36%) and Bacilli (24%) were well represented, while in Site 3 strains were mainly affiliated to classes Actinobacteria (35%), γ-Proteobacteria (35%), and β-Proteobacteria (12%). The order of metal(loid) toxicity for the isolated strains was Cd > As > Zn. Overall, 10 strains grew at 500 mg Cd L(-1) , 1000 mg Zn L(-1) , and 500 mg As L(-1) , being considered the most metal(loid)-tolerant bacteria. These strains belonged to genera Cupriavidus, Burkholderia, Novosphingobium, Sphingobacterium, Castellaniella, Mesorhizobium, Chryseobacterium, and Rhodococcus and were mainly retrieved from Site 1. The multiple metal(loid)-tolerant strains isolated in this study have potential to be used in bioremediation/phytoremediation.

Response of Arbuscular Mycorrhizal Fungi to Hydrologic Gradients in the Rhizosphere of Phragmites australis (Cav.) Trin ex. Steudel Growing in the Sun Island Wetland.

Within the rhizosphere, AM fungi are a sensitive variable to changes of botanic and environmental conditions, and they may interact with the biomass of plant and other microbes. During the vegetative period of the Phragmites australis growing in the Sun Island Wetland (SIW), the variations of AM fungi colonization were studied. Root samples of three hydrologic gradients generally showed AM fungi colonization, suggesting that AM fungi have the ability for adaptation to flooded habitats. There were direct and indirect hydrological related effects with respect to AM fungi biomass, which interacted simultaneously in the rhizosphere. Though water content in soil and reed growth parameters were both positively associated with AM fungi colonization, only the positive correlations between reed biomass parameters and the colonization could be expected, or both the host plant biomass and the AM fungi could be beneficial. The variations in response of host plant to the edaphic and hydrologic conditions may influence the effectiveness of the plant-mycorrhizal association. This study included a hydrologic component to better assess the role and distribution of AM fungi in wetland ecosystems. And because of that, the range of AM fungi was extended, since they actually showed a notable adaptability to hydrologic gradients.

Bioenergy and Biomass Utilization.

Bioenergy is of increasing interest as a renewable, environmentally friendly alternative to energy derived from fossil fuels. Through a variety of processes, biomass can be converted to solid, liquid, or gaseous biofuels. However, various challenges persist to the maintenance and development of biomass-to-energy utilization. This special issue focuses on the most recent advances in the frontier research of bioenergy and biomass utilization and features six selected papers with high quality. The paper titled “Nanofibrillated Cellulose and Copper Nanoparticles Embedded in Polyvinyl Alcohol Films for Antimicrobial Applications” by T. Zhong et al. develops a method to produce hybrids of TEMPO nanofibrillated cellulose (TNFC) and copper nanoparticles. The hybrid material is embedded in polyvinyl alcohol thermoplastic resin and the films are produced using a solvent casting method. The authors evaluate the films in terms of its morphology and thermal and antimicrobial properties and prove that TNFC-copper nanoparticles as antimicrobial nanofillers are valuable for PVA applications. The paper titled “Response of Arbuscular Mycorrhizal Fungi to Hydrologic Gradients in the Rhizosphere of Phragmites australis (Cav.) Trin ex. Steudel Growing in the Sun Island Wetland” by L. Wang et al. assesses the variations of hydrologic gradients in the relationships among AM fungi, reed, and rhizospheric microorganisms. The authors discover water content in soil and reed growth parameters are both positively associated with AM fungi colonization, but only the positive correlations between reed biomass parameters and the colonization could be expected, or both the host plant biomass and the AM fungi could be beneficial. This study could shed light on the mechanisms inside AM fungi-reed symbioses and would be referred to for optimizing the combined phytorhizoremediation. The paper titled “Production by Tobacco Transplastomic Plants of Recombinant Fungal and Bacterial Cell-Wall Degrading Enzymes to Be Used for Cellulosic Biomass Saccharification” by L. Paolo et al. presents work on saccharification of plant biomass. The authors express in tobacco chloroplasts microbial genes encoding five cellulases and a polygalacturonase. Leaf extracts containing the recombinant enzymes show the ability to degrade various cell-wall components under different conditions. In addition, a thermostable xylanase is also tested in combination with a cellulase and a polygalacturonase to study the cumulative effect on the depolymerization of a complex plant substrate. Results demonstrate the feasibility of using transplastomic tobacco leaf extracts to convert cell-wall polysaccharides into reducing sugars, fulfilling a major prerequisite of large scale availability of a variety of cell-wall degrading enzymes for biofuel industry. The paper titled “Enzymatic Saccharification of Lignocellulosic Residues by Cellulases Obtained from Solid State Fermentation Using Trichoderma viride” by T. Sartori et al. presents an approach that uses cellulolytic complex produced by Trichoderma viride in solid state fermentation to hydrolyze lignocellulosic residues. This produced enzyme shows viability in comparison with the commercial cellulase enzyme. The synthesis of cellulases by microorganisms from lignocellulosic residues is a process of great interest, representing the search for renewable sources to replace the fossil energetic matrix. The paper titled “Improving Biomethane Production and Mass Bioconversion of Corn Stover Anaerobic Digestion by Adding NaOH Pretreatment and Trace Elements” by C. Liu et al. describes an approach to improve biomethane production from corn stover. The authors use NaOH pretreatment and trace elements supplementation as a strategy to enhance the biodegradability of corn stover for biomethane production. The approach is compared with only NaOH-pretreated and untreated corn stover, and the paper highlights the supplementation of trace elements. The paper titled “Biochemical Modulation of Lipid Pathway in Microalgae Dunaliella sp. for Biodiesel Production,” by A. F. Talebi et al., explores the use of myoinositol to modulate LP and biodiesel quality. Inclusion of myoinositol in the media indeed improves the total lipid accumulation and biodiesel quality parameters, and this work highlights the fact that the biochemical modulation strategies should be progressively considered in the hope of finding more efficient and economically feasible strategies leading to more viable production systems.

Characterization of the microbial community in the rhizosphere of Phragmites australis (cav.) trin ex. steudel growing in the Sun Island Wetland.

Rhizospheric microorganisms are important for environmental conservancy. The constancy and variability of the microorganisms in the rhizosphere of Phragmites australis in relation to the spatiotemporal variations in wetland ecosystems were studied. During the peak and trough of the vegetative period of the Phragmites australis growing across the hydrologic gradients of the Sun Island Wetland, Biolog and denaturing gradient gel electrophoresis (DGGE) were used to investigate the rhizospheric microbial characteristics. Both methods demonstrated that the microbial activity, richness, and diversity decreased from summer to autumn. However, these properties did not show significant correlation with hydrologic gradient, except that the genetic richness and diversity of the fungi decreased with it. Cluster analysis also demonstrated that the rhizospheric microbial community seemed to be largely affected by a vegetative period. In addition, this research was extended to a broader range of determining the universal microorganisms, which showed notable adaptability.

Effects of organochlorines on microbial diversity and community structure in Phragmites australis rhizosphere

This study investigated the impacts of an organochlorine (OC, γ-hexachlorocyclohexane and chlorobenzenes) mixture on microbial communities associated to Phragmites australis rhizosphere. Seventy-eight distinct colony morphotypes were isolated, cultivated and analysed by 16S rDNA sequence analysis. Toxicity tests confirmed sensitivity (e.g. Hevizibacter, Acidovorax) or tolerance (e.g. Bacillus, Aeromonas, Pseudomonas, Sphingomonas) of isolates. Rhizosphere analysis by pyrosequencing showed the microbial adaptation induced by OC exposure. Among the most abundant molecular operational taxonomic units, 80% appeared to be tolerant (55% opportunist, 25% unaffected) and 20% sensitive. P. australis rhizosphere exposed to OCs was dominated by phylotypes related to α-, β- and γ-Proteobacteria. Specific genera were identified which were previously described as chlorinated organic pollutant degraders: Sphingomonas sp., Pseudomonas sp., Devosia sp. and Sphingobium sp. P. australis could be suitable plants to maintain their rhizosphere active microbial population which can tolerate OCs and potentially improve the OC remediation process in part by biodegradation.