Variation of the Bacterial Community in the Rhizoplane Iron Plaque of the Wetland Plant Typha latifolia

Phytomitigation potential and adaptive responses of helophyte Typha latifolia L. to copper smelter-influenced heavily multi-metal contamination

The present study of phytomitigation potential and adaptive physiological and biochemical responses of helophyte Typha latifolia L. growing in water bodies at different distances from the century-old copper smelter (JSC "Karabashmed" Chelyabinsk Region, Russia) was conducted for the first time. This enterprise is one of the most dominant sources of multi-metal contamination for water and land ecosystems. The aim of the research was to assess the heavy metal (Cu, Ni, Zn, Pb, Cd, Mn, and Fe) accumulation, the photosynthetic pigment complex, and some redox reactions in T. latifolia from six differently technogenic impacted sites. In addition, the quantity of mesophilic aerobic and facultative anaerobic microorganisms (QMAFAnM) in rhizosphere sediments, as well as some plant growth-promoting (PGP) attributes of 50 isolates from each site, were determined. The water and sediment metal concentrations in highly contaminated sites exceeded the permissible/critical limits and were found much higher than that previously reported by other researchers while studying this helophyte. Both the degree of contamination and geoaccumulation indexes further elucidated extremely high contamination due to prolonged activity of copper smelter. T. latifolia accumulated significantly higher concentrations of the most of studied metals in its roost and rhizome with meager transfer to leaves (the translocation factors were less than one). Spearman's rank correlation coefficient showed a strong positive correlation between the metal concentration in sediments and its content in T. latifolia leaves (rs = 0.786 at p < 0.001 on average) and roots/rhizome (rs = 0.847 at p < 0.001 on average). In highly contaminated sites, the folia content of chlorophyll a and carotenoids decreased (by 30 and 38%, respectively), while lipid peroxidation enhanced (by 42%) on average compared to S1-S3 sites. These responses were accompanied by increasing non-enzymatic antioxidant content (soluble phenolic compounds, free proline, and soluble thiols) that allow plants to resist under significant anthropogenic loads. QMAFAnM in the five studied rhizosphere substrates varied insignificantly (2.5 × 106 - 3.8 × 107 cfu g-1 DW) and was decreased only in the most contaminated site (4.5 × 105). The proportion of rhizobacteria capable of fixing atmospheric nitrogen decreased by 1.7 times, solubilizing phosphates by 1.5 times, and synthesizing indol-3-acetic acid by 1.4 times in highly contaminated sites, while the amount of siderophore, 1-aminocyclopropane-1-carboxylate deaminase, and HCN producing bacteria did not considerably change. The results indicate high resistance of T. latifolia to prolonged technogenic impact, probably due to compensatory adaptive changes in the nonenzymatic antioxidant level and presence of beneficial microorganisms. Thus, T. latifolia was found to be a promising metal-tolerant helophyte that could help in mitigation of metal toxicity due to their phytostabilization even in heavily contaminated environment.

Purification and water resource circulation utilization of Cd-containing wastewater during microbial remediation of Cd-polluted soil

The purification and water resource circulation utilization of cadmium-containing leachate is a key link in the field application of microbial remediation in Cd-polluted soil. In this study, through a simulation experiment of microbial remediation of Cd-polluted paddy soil, the feasibility of the purification and recycling process of wastewater derived from microbial remediation of Cd-polluted soil was explored. The results of the microbial mobilization and removal experiment showed that the concentrations of Cd, N, P, and K in the leachate were 88.51 μg/L, 38.06, 0.53, and 98.87 mg/L, respectively. The leachate also contained a large number of microbial resources, indicating that it had high recovery values. To recycle this wastewater, activated carbon (C), humic acid (H), and self-assembled monolayers on mesoporous supports (SAMMS; S) were used as adsorbents. The results showed that the co-existing cations in the leachate had a major influence on the adsorption of Cd. In the ternary system of Fe, Al, and Cd, the removal efficiency of Cd increased to 91.2% when the S dosage was increased to 5‰, and the sorption of Cd occurred after Fe and Al. However, C and H exhibited poor adsorption performances. The isotherm models further showed that the maximum adsorption capacities of S, H, and C were 13.96, 6.41 and 2.94 mg/g, respectively. The adsorption kinetics of S showed that adsorption was a rapid process, and the C-H and O-Si-O of S were the key functional groups. The pH of the leachate significantly affected the adsorption efficiency of Cd. Finally, the purified leachate was successfully applied to microbial cultivation and soil remediation. Overall, the reclamation of Cd-containing wastewater can not only dampen the impacts of water shortages, but also achieve the purposes of Cd removal and resource recovery to lower costs by approximately 1166-3499 yuan per mu.

Phytoremediation mechanisms and plant eco-physiological response to microorganic contaminants in integrated vertical-flow constructed wetlands

Vegetations play a vital role in the ecological function of constructed wetlands (CW), but the systemic phytoremediation mechanism of CW is still unclear. An integrated vertical-flow constructed wetland (IVCW) was established to elucidate the phytoremediation mechanisms and plants eco-physiological response to an emerging contaminant, sulfamethoxazole (SMX). Attenuation of SMX in IVCW with and without vegetation (Acorus calamus) are comparatively analyzed. The results showed significant enhancement of removal efficiencies of total nitrogen (via intensified denitrification) and SMX by up to 10% respectively with vegetation. A unique micro-rhizo environment was created by stimulating the denitrifiers, Clostridium_sensu_stricto, Ignavibacterium, Rhodanobacter, and Geobacter. Free-living plant growth-promoting bacteria, unclassified_Burkholderiales and unclassified_Betaproteobacteria, proliferated in the rhizosphere, protecting the growth mechanism of A. calamus and, consequently, promoting performance of the IVCW. Overall, A. calamus exhibited tolerance to SMX, maintaining its photosynthesis rate and stabilizing the plant cell structure by an effective antioxidant system. The growth and defense mechanisms of A. calamus appeared to positively correlate with the IVCW performance, whereby the photosynthetic rate and antioxidant enzymes activities peaked together with the maximum removal efficiency of TN (77.81%) and SMX (99.88%). The contribution of vegetation to ecotoxicity reduction in CW might be underrated as absorbed SMX could be phytodegraded into less toxic metabolites via specific enzymes.

Unraveling Fe(II)-Oxidizing Mechanisms in a Facultative Fe(II) Oxidizer, Sideroxydans lithotrophicus Strain ES-1, via Culturing, Transcriptomics, and Reverse Transcription-Quantitative PCR

Sideroxydans lithotrophicus ES-1 grows autotrophically either by Fe(II) oxidation or by thiosulfate oxidation, in contrast to most other isolates of neutrophilic Fe(II)-oxidizing bacteria (FeOB). This provides a unique opportunity to explore the physiology of a facultative FeOB and constrain the genes specific to Fe(II) oxidation. We compared the growth of S. lithotrophicus ES-1 on Fe(II), thiosulfate, and both substrates together. While initial growth rates were similar, thiosulfate-grown cultures had higher yield with or without Fe(II) present, which may give ES-1 an advantage over obligate FeOB. To investigate the Fe(II) and S oxidation pathways, we conducted transcriptomics experiments, validated with reverse transcription-quantitative PCR (RT-qPCR). We explored the long-term gene expression response at different growth phases (over days to a week) and expression changes during a short-term switch from thiosulfate to Fe(II) (90 min). The dsr and sox sulfur oxidation genes were upregulated in thiosulfate cultures. The Fe(II) oxidase gene cyc2 was among the top expressed genes during both Fe(II) and thiosulfate oxidation, and addition of Fe(II) to thiosulfate-grown cells caused an increase in cyc2 expression. These results support the role of Cyc2 as the Fe(II) oxidase and suggest that ES-1 maintains readiness to oxidize Fe(II), even in the absence of Fe(II). We used gene expression profiles to further constrain the ES-1 Fe(II) oxidation pathway. Notably, among the most highly upregulated genes during Fe(II) oxidation were genes for alternative complex III, reverse electron transport, and carbon fixation. This implies a direct connection between Fe(II) oxidation and carbon fixation, suggesting that CO2 is an important electron sink for Fe(II) oxidation. IMPORTANCE Neutrophilic FeOB are increasingly observed in various environments, but knowledge of their ecophysiology and Fe(II) oxidation mechanisms is still relatively limited. Sideroxydans isolates are widely observed in aquifers, wetlands, and sediments, and genome analysis suggests metabolic flexibility contributes to their success. The type strain ES-1 is unusual among neutrophilic FeOB isolates, as it can grow on either Fe(II) or a non-Fe(II) substrate, thiosulfate. Almost all our knowledge of neutrophilic Fe(II) oxidation pathways comes from genome analyses, with some work on metatranscriptomes. This study used culture-based experiments to test the genes specific to Fe(II) oxidation in a facultative FeOB and refine our model of the Fe(II) oxidation pathway. We gained insight into how facultative FeOB like ES-1 connect Fe, S, and C biogeochemical cycling in the environment and suggest a multigene indicator would improve understanding of Fe(II) oxidation activity in environments with facultative FeOB.