Integrity of lichen cell membranes as an indicator of heavy-metal pollution levels in soil

Physiological alterations and heavy metal accumulation in the transplanted lichen Pyxine cocoes (Sw.) Nyl. in Lucknow city, Uttar Pradesh

Air pollution has become a major concern due to its detrimental effects on living beings. The present study is aimed at assessing the current status of air pollution in Lucknow city using lichen transplantation technique and assesing its effect on physiology of Pyxine cocoes. The samples of P. cocoes were collected from relatively pollution-free area Malihabad and transplanted in 10 designated sites in five regions for 30 days. Various parameters such as heavy metals, chlorophyll pigments, carotenoid, chlorophyll degradation, and electrolyte conductivity were estimated in transplanted lichens. The study revealed that the concentration of all 10 heavy metals was higher in all transplanted samples than in the control sample, which was found in order of Al > Fe > Mn > Zn > Cu > Cr > Pb > Ni > Co > Cd. Among all 10 transplanted sites, the significantly increased accumulation of aluminum (5.11 to 5.47 µg L-1), iron (4.73 to 5.46 µg L-1), manganese (110.99 to 144.58 µg g-1), and zinc (87.96 to 97.40 µg g-1) was found in Charbagh, Qaisarbagh, and Alambagh sites. Further, in all samples, chlorophyll a (3.98 µg L-1), chlorophyll b (1.22 µg L-1), total chlorophyll (5.20 µg L-1), and chlorophyll degradation (0.55 µg g-1) were significantly decreased, whereas elevated levels of carotenoid (0.71 µg g-1), and electrolyte conductivity (64.99 µS cm-1), were observed. The scanning electron microscope (SEM) investigated the morphological changes in transplanted lichen samples, and significant damage to the anatomy of mycelium was found in most of the polluted site's samples, which correlated with the pollution levels. The present study clearly demonstrated that the transplanted lichen P. cocoes is an efficient bioaccumulator and bioindicator of air quality in urban environments.

Why Bufo gargarizans tadpoles grow bigger in Pb-contaminated environments? The gut microbiota matter

The impacts of lead/Pb2+ on ecosystems have received widespread attention. Growth suppression is a major toxic effect of Pb compounds on aquatic animals, however, some studies have also reported their growth-promoting effects. These complex outcomes may be explained by anions that accompany Pb2+ or by the multiple toxic mechanisms/pathways of Pb2+. To examine these hypotheses, we tested how Bufo gargarizans tadpoles responded to Pb(NO3)2 (100 and 200 μg/L Pb2+) using transcriptomics and microbiomics, with NaNO3 and blank groups as controls. Tadpoles exposed to Pb(NO3)2 showed delayed development while increased somatic growth in a dose-dependent manner, which can be attributed to the effects of NO3- and Pb2+, respectively. Tadpole transcriptomics revealed that exposure to NO3- downregulated the MAPK pathway at transcriptional level, explaining the development-suppressing effect of NO3-; while Pb2+ upregulated the transcription of detoxification pathways (e.g., xenobiotics metabolism by cytochrome P450 and glutathione metabolism), indicating cellular stress and thus contradicting the growth advantage of Pb2+-exposed tadpoles. Pb2+ exposure changed the tadpole gut microbiota drastically, characterized by increased polysaccharides and carbohydrate utilization while decreased fatty acid and amino acid consumption according to microbial functional analysis. Similar gut microbial variations were observed in field-collected tadpoles from different Pb2+ environments. This metabolic shift in gut microbiota likely improved the overall food utilization efficiency and increased the allocation of fatty acids and amino acids to the host, explaining the growth advantage of Pb2+-exposed tadpoles. In summary, our results suggest multiple toxic pathways of Pb2+, and the gut microbiota may affect the pollution outcomes on animals.

Do urban air pollutants induce changes in the thallus anatomy and affect the photosynthetic efficiency of the nitrophilous lichen Physcia adscendens?

Lichens are symbiotic organisms that are generally sensitive to air pollution due to their specific biological and physiological features. Physcia adscendens is a nitrophilous lichen well-known for being resistant to air pollution associated with progressive anthropopressure. The aim of this study was to investigate the effect of nitrogen oxides and suspended particulate matter (PM10 and PM2.5) on anatomical structure of the thallus and photobiont's photosynthetic efficiency in P. adscendens inhabiting sites that differ in terms of air pollution level and thereby to determine the relevance of these pollutants for shaping the structure of the thallus and the physiological condition of the photosynthetic partner. We found that P. adscendens from polluted sites had increased thickness of the algal layer and the larger size of the algae cells, but a much lower ratio of the algal layer to the whole thallus. Lichens from highly polluted sites had also higher photosynthetic efficiency, which indicates a relatively good physiological condition of the photobiont. This indicates that the photobiont of P. adscendens is well-adapted to function under air pollution stress which may contribute to its success in colonizing polluted sites. Both changes in the anatomy of the lichen thallus and the efficiency of photosynthesis may be related to the enrichment of the environment with nitrogen. The increased photosynthetic efficiency as well as investment in the size of photobiont cells and growth mycobiont hyphae confirms that P. adscendens is well-adapted to urban conditions; however, the mechanism behind those adaptations needs more focus in the context of global environmental changes.

Application potential of Vaccinium ashei R. for cadmium migration retention in the mining area soil

Despite numerous reports on phytoremediation of heavy metals contaminated soil, there are few reports on plant retention of heavy metals in the mining area slope. This study was the first of its kind to explore the cadmium (Cd) retention capacity of the blueberry (Vaccinium ashei Reade). Firstly, we investigated the stress response of blueberry to different soil Cd concentrations (1, 5, 10, 15, 20 mg/kg) to assess its potential for phytoremediation by pot experiments. The results showed that the blueberry biomass exposed to 10 and 15 mg/kg Cd was significantly increased compared with the control (1 mg/kg Cd); the blueberry crown increased by 0.40% and 0.34% in 10 and 15 mg/kg Cd-contaminated soil, respectively, compared with control; the blueberry heigh did not even change significantly in each treatment group; the total chlorophyll content, peroxidase and catalase activity of blueberry were enhanced in 5-20 mg/kg Cd treatments. Furthermore, the Cd contents of blueberry in the root, stem and leaf increased significantly as the Cd concentration of soil increased. We found that more Cd accumulated in blueberry root: the bioaccumulation concentration factor was root > stem > leaf for all groups; the residual-Cd (Cd speciation) in soil increased by 3.83%-411.11% in blueberry-planted versus unplanted groups; blueberry improved the Cd-contaminated soil micro-ecological environment including soil organic matter, available K and P, as well as microbial communities. Then, to investigate the effect of blueberry cultivation on Cd migration, we developed a bioretention model and revealed that soil Cd transport along the model slope was significantly weakened by blueberry cultivation, especially at the bottom of the model. In a word, this research suggests a promising method for the phytoremediation of Cd-contaminated soil and the reduction of Cd migration in mining areas.

Accumulation of Cadmium in Transplanted Lichen Pyxine cocoes (Sw.) Nyl., with Reference to Physiochemical Variation and Kinetics of Cadmium Biosorption

The present study aims to signify the role of Pyxine cocoes (Sw.) Nyl. (P. cocoes) as cadmium (Cd) biomonitor in atmosphere. This was achieved by quantifying the amount of Cd accumulated in transplanted P. cocoes, when stimulated with known concentrations of Cd (5µM, 50µM, 100µM, 150µM and 200µM) at increasing intervals of time up-to 40 days. All the five concentrations exhibited increasing trend of accumulation with time. As depicted by Pearson's Correlation (at p < 0.001), anti-oxidative enzymes (superoxide dismutase r= -0.812, ascorbate peroxidase r= -0.802, catalase r= -0.757) and electrical conductivity (r = 0.693) were the most efficient parameters to depict increased Cd presence in atmosphere. In the current study, accumulation of Cd by transplanted lichen has been first time analyzed by biosorption kinetics. The uptake of Cd by P. cocoes followed pseudo-second-order kinetics (range of R₂² value was 0.969-0.998). The marker parameters in combination with the ability to accrue Cd fortifies P. cocoes's role as a biomonitor.

Interaction effect of fungicide and chitosan on non-target lichenized fungi

Excessive use of plant growth stimulants and pesticides is currently a considerable problem, especially in agriculture, horticulture, and arboriculture. Understanding the impacts of these compounds and their combinations on non-target organisms is crucial to minimize unintended consequences, while maintaining their use in plant protection. The aim of this study was to test how long-term spraying with different solutions of natural biostimulator chitosan, synthetic fungicide Switch 62.5 WG, and their combinations affects the physiology of epiphytic lichen Xanthoria parietina naturally occurring in fruit orchards and farmlands. We showed that fungicides composed of fludioxionil and cypronidil, as well as the combined use of such fungicides together with chitosan, can cause the considerable impairment of lichen physiology, and these disturbances relate to both algal and fungal partners of the symbiotic association. This negative effect was especially visible in the loss of cell membrane integrity, the high level of membrane lipid peroxidation, and changes in chlorophyll fluorescence parameters on the last day of the experiment. The combined use of these agents also leads to clear disturbances in the functioning of the mitochondrial respiratory chain, which was manifested by increased NADH dehydrogenase activity, while the use of these compounds separately led to a decrease in the activity of this enzyme. We concluded that the regular use of these agents in fruit tree cultivation may cause serious ecological consequences for epiphytic lichen communities as a result of the death of lichen thalli. This study suggests that the impact of some plant protection agents, both individually and in combinations, merits further attention in terms of their impact on non-target fungi.

Cascading effects of Pb on the environmental and symbiotic microbiota and tadpoles' physiology based on field data and laboratory validation

Heavy metal pollution poses a serious threat to ecosystems. Currently, there is a lack of field data that would enable us to gain a systematic understanding of the influences of heavy metals on aquatic ecosystems, especially the interactions between environments and animals. We studied the relationships between the variations in heavy metal concentrations (10 species including Pb in sediments and surface water), the community structure of environmental and symbiotic microbiota, and the gut traits of Bufo gargarizans tadpoles across 16 sampling sites on the Chengdu Plain through rigorous statistical analysis and laboratory validation. The results show that heavy metal concentrations, especially the Pb concentration of the sediment, are linked to the variations in sediment and tadpoles' gut microbiomes but not to water microbiota. For the sediment microbiota, Pb causes a trade-off between the proportions of Burkholderiales and Verrucomicrobiae and affects the methane, sulfide, and nitrate metabolisms. For tadpoles, a high sediment Pb content leads to a low abundance of gut aerobic bacteria and a large relative gut weight under both field and laboratory conditions. In addition, Pb promotes the growth of B. gargarizans tadpoles under laboratory conditions. These effects seem to be beneficial to tadpoles. However, a high Pb content leads to a low abundance of probiotic bacteria (e.g., Verrucomicrobiae, Eubacteriaceae, and Cetobacterium) and a high abundance of pathogenic bacteria in the gut and environment, suggesting potential health risks posed by Pb. Interestingly, there is a causal relationship between Pb-induced variations in sediment and symbiotic microbiotas, and the latter is further linked to the variation in relative gut weight of tadpoles. This suggests a cascading effect of Pb on the ecosystem. In conclusion, our results indicate that among the heavy metals, the Pb in sediment is a critical factor affecting the aquatic ecosystem through an environment-gut-physiology pathway mediated by microbiota.

Combined effect of acute salt and nitrogen stress on the physiology of lichen symbiotic partners

Nitrogen pollution and excessive salinity are commonly regarded as one of the major environmental concerns in recent decades in many urban environments. Although in urban areas lichens are exposed to both salt and nitrogen stress, no studies have been conducted to date on the simultaneous impact and interaction of these factors on lichen physiology. The aim was to determine the effect of various combinations of NaCl and NH4NO3 doses on the physiology of epigeic lichen Cladonia rei. We also aimed to compare the response of lichens collected from polluted and unpolluted sites to verify whether lichens exposed to different levels of environmental stress in their native environment will react differently. The combined salt-nitrogen treatment caused significant disturbances in the integrity of cell membranes and chlorophyll fluorescence parameters. The most detrimental effect concerned the loss of cell membrane integrity, which suggests that this parameter can serve as a relevant indicator of acute salt-nitrogen stress incidents. Salt stress decreased the photosynthetic efficiency 1 h after exposure, but after 72 h, the FV/FM returned to the level characteristic of healthy lichens in experimental groups without and with small doses of ammonium nitrate. In contrast, recovery was not possible in combination with high nitrogen doses. This indicates that exposure to short-term salt stress in a nitrogen-poor environment only causes a temporary reduction in photosynthetic efficiency, but in urban eutrophic environments may have more serious consequences. The weakened physiological condition of the mycobiont manifested by an increased level of cell membrane damage and a persistent decrease in the photosynthetic efficiency of the photobiont in lichens growing along the roads may indicate an excess of nitrogen in the environment, enhanced by the effect of salt. Lichens collected from a heavy-metal-polluted habitat responded more strongly than those from an unpolluted habitat suggesting that in lichens previously affected by certain harmful factors, exposure to another stress factor may lead to greater disturbances. This is of particular importance for lichens inhabiting the vicinity of roads, since they are also under the influence of other pollutants emitted by road traffic.

Multi-omics provide mechanistic insight into the Pb-induced changes in tadpole fitness-related traits and environmental water quality

Water pollution from lead/Pb²⁺ poses a significant threat to aquatic ecosystems, and its repercussions on aquatic animals have received considerable attention. Although Pb²⁺ has been found to affect numerous aspects of animals, including individual fitness, metabolic status, and symbiotic microbiota, few studies have focused on the associations between Pb²⁺-induced variations in fitness, metabolome, symbiotic microbiome, and environmental parameters in the same system, limiting a comprehensive understanding of ecotoxicological mechanisms from a holistic perspective. Moreover, most ecotoxicological studies neglected the potential contributions of anions to the consequences generated by inorganic lead compounds. We investigated the effects of Pb(NO₃)₂ at environmentally relevant concentrations on the Rana omeimontis tadpoles and the water quality around them, using blank and NaNO₃-treated groups as control. Results showed that Pb(NO₃)₂ not only induced a rise in water nitrite level, but exposure to this chemical also impaired tadpole fitness-related traits (e.g., growth and development). The impacts on tadpoles were most likely a combination of Pb²⁺ and NO₃^-. Tissue metabolomics revealed that Pb(NO₃)₂ exposure influenced animal substrate (i.e., carbohydrate, lipid, and amino acid) and prostaglandin metabolism. Pb(NO₃)₂ produced profound shifts in gut microbiota, with increased Proteobacteria impairing Firmicutes, resulting in higher aerobic and possibly pathogenic bacteria. NaNO₃ also influenced tadpole metabolome and gut microbiome, in a manner different to that of Pb(NO₃)₂. The presence of NO₃^- seemed to counteract some changes caused by Pb²⁺, particularly on the microbiota. Piecewise structural equation model and correlation analyses demonstrated connections between tissue metabolome and gut microbiome, and the variations in tadpole phenotypic traits and water quality were linked to changes in tissue metabolome and gut microbiome. These findings emphasized the important roles of gut microbiome in mediating the effects of toxin on aquatic ecosystem. Moreover, it is suggested to consider the influences of anions in the risk assessment of heavy metal pollutions.

Towards understanding the effect of heavy metals on mycobiont physiological condition in a widespread metal-tolerant lichen Cladonia rei

Heavy metals present in the environment can cause a variety of injury symptoms in various organisms including lichens. Most studies examined metal-induced stress under controlled laboratory conditions, and little is known about actual response of lichens in their natural habitat. This study aims to recognize the effect of heavy metal accumulation (total and intracellular) on lichen physiological and biochemical parameters specifically related to the functioning of fungal component. Cladonia rei was used as a model species due to its common occurrence both in unpolluted and extremely polluted sites. We observed a decline in the fungal metabolism which was expressed by a decrease in ergosterol content and an increase in cell membrane damage as a result of increased Zn, Cd, Cu and Ni accumulation. Additionally, the results indicated that increased accumulation of xenobiotics (Pb and As) caused reduction of glutathione (GSH) concentrations and increased membrane lipid peroxidation. Therefore, we conclude that GSH does not provide high oxidative stress protection in C. rei which is somewhat against its insensitivity to pollution. The reduced pool of GSH could be explained by its oxidation to glutathione disulphide induced by heavy metal stress or its use for phytochelatin (PC) synthesis. The content of secondary metabolites was not related to heavy metal accumulation and remained at a relatively stable level. This indicates that the decline in the physiological condition did not weaken the mycobiont of C. rei enough to inhibit the synthesis of secondary metabolites and their precursors were supplied at a sufficient level. Thus, the potential function of main secondary metabolites as extracellular metal immobilizers and antioxidants is still possible even in individuals growing at extremely polluted sites. Despite the evident heavy metal stress, C. rei copes well and spreads easily through extremely polluted environments, which underlines its unique pioneering abilities in highly disturbed sites.

A review on the use of lichens as a biomonitoring tool for environmental radioactivity

Lichens have been widely used as a biomonitoring tool to record the distribution and concentration of airborne radioactivity and pollutants such as metals. There are limitations, however: although pollutants can be preserved in lichen tissues for long periods of time, not all radioactive and inert elements behave similarly. The chemical species of elements at the source, once captured, and the mode of storage within lichens play a role in this biomonitoring tool. Lichens are a symbiotic association of an algal or cyanobacterial partner (photobiont) with a fungal host (mycobiont). Lichens grow independently of the host substrates, including rocks, soils, trees and human-made structures. Lacking a root system, lichen nutrient or contaminant uptake is mostly through direct atmospheric inputs, mainly as wet and dry deposition. As lichens grow in a large variety of environments and are resilient in harsh climates, they are adapted to capture and retain nutrients from airborne sources. The context of this review partially relates to future deployment of small modular reactors (SMRs) and mining in remote areas of Canada. SMRs have been identified as a future source of energy (electricity and heat) for remote off-grid mines, potentially replacing diesel fuel generation facilities. For licensing purposes, SMR deployment and mine development requires capabilities to monitor background contaminants (natural radioactivity and metals) before, during and after deployment, including for decommissioning and removal. Key aspects reviewed herein include: (1) how lichens have been used in the past to monitor radioactivity; (2) radiocontaminants capture and storage in lichens; (3) longevity of radiocontaminant storage in lichen tissues; and (4) limitations of lichens use for monitoring radiocontaminants and selected metals.

Metabolic processes involved with sugar alcohol and secondary metabolite production in the hyperaccumulator lichen Diploschistes muscorum reveal its complex adaptation strategy against heavy-metal stress

The synthesis of various unique secondary metabolites by lichens is the result of mutualistic symbiotic association between the mycobiont and autotrophic photobiont. The function of these compounds and causal factors for their production are not fully understood. This paper examines the effect of heavy-metal bioaccumulation and physiological parameters related to photosynthesis and carbon metabolism on the production of lichen substances in hyperaccumulator Diploschistes muscorum. The obtained model of secondary metabolite concentrations in the thalli demonstrates that the carbon source provided by the photobiont and associated polyols produced by the mycobiont have positive impact on the production; on the contrary, the increased intracellular load of heavy metals and excessive loss of cell membrane integrity adversely affected secondary metabolite contents. Additionally, the production of secondary metabolites appears to be more dependent on intracellular metal concentrations than on soil pollution level. To compensate for metal stress, both efficient functioning of algal component and sufficient production of secondary metabolites are required. The balanced physiological functioning of mycobiont and photobiont constitutes the complex protective mechanism to alleviate the harmful effects of heavy metal stress on primary and secondary metabolism of lichens.

The physiological response of different tobacco varieties to chilling stress during the vigorous growing period

Tobacco is be sensitively affected by chilling injury in the vigorous growth period, which can easily lead to tobacco leaf browning during flue-curing and quality loss, however, the physiological response of tobacco in the prosperous period under low temperature stress is unclear. The physiological response parameters of two tobacco varieties to low temperature stress were determined. The main results were as follows: ① For tobacco in the vigorous growing period subjected to low-temperature stress at 4-16 °C, the tissue structure of chloroplast changed and photosynthetic pigments significantly decreased compared with each control with the increase of intensity of low-temperature stress. ② For tobacco in the vigorous growing period at 10-16 °C, antioxidant capacity of the protective enzyme system, osmotic adjustment capacity of the osmotic adjusting system and polyphenol metabolism in plants gradually increased due to induction of low temperature with the increase of intensity of low-temperature stress. ③ Under low-temperature stress at 4 °C, the protective enzyme system, osmotic adjusting system and polyphenol metabolism of the plants played an insignificant role in stress tolerance, which cannot be constantly enhanced based on low-temperature resistance at 10 °C. This study confirmed that under the temperature stress of 10-16 °C, the self-regulation ability of tobacco will be enhanced with the deepening of low temperature stress, but there is a critical temperature between 4 and 10 °C. The self-regulation ability of plants under low temperature stress will be inhibited.

Effects of native forest and human-modified land covers on the accumulation of toxic metals and metalloids in the tropical bee Tetragonisca angustula

The intensive shift on land cover by anthropogenic activities have led to changes in natural habitats and environmental contamination, which can ultimately impact and threat biodiversity and ecosystem services, such as pollination. The aim of this study was to evaluate the effect of native forest and human-modified land covers on the concentrations of chemical elements accumulated in the neotropical pollinator bee T. angustula. Eight landscapes, within an Ecological Corridor in the State of São Paulo, Brazil, with gradients of forest cover, spatial heterogeneity and varying land covers were used as sampling unities. Bees collected in traps or through actives searches had the concentration of 21 chemical elements determined by ICP-MS. Results show a beneficial effect of forested areas on the concentrations of some well-known toxic elements accumulated in bees, such as Hg, Cd, and Cr. Multivariate Redundancy Analysis (RDA) suggests road as the most important driver for the levels of Cr, Hg, Sb, Al, U, As, Pb and Pt and bare soil, pasture and urban areas as the landscape covers responsible for the concentrations of Zn, Cd, Mn, Mg, Ba and Sr in bees. The results reinforce the potential use of T. angustula bees as bioindicators of environmental quality and also show that these organisms are being directly affected by human land use, offering potential risks for the Neotropical ecosystem. Our study sheds light on how land covers (native forest and human-modified) can influence the levels of contaminants in insects within human-dominated landscapes. The generation of predictions of the levels of toxic metals and metalloids based on land use can both contribute to friendly farming planning as well as to support public policy development on the surrounding of protected areas and biodiversity conservation hotspots.

Tree decay modulates the functional response of lichen communities in Patagonian temperate forests

Epiphytic and epixylic lichens respond negatively to forest degradation, climate change and pollution, but those effects may depend on functional traits or interact with the stage of tree decay. Disentangling the main drivers of lichen communities remains a challenge in regions where lichens are diverse and poorly known, as the case of Patagonian temperate forests. We used a multi-scale approach to evaluate the relationship between environmental variables, tree decay stage and lichens. We sampled lichens across three increasing scales (tree ≪ site ≪ landscape) by selecting 19 landscape units, where trees in four decay stages (snags, logs, cavity trees and healthy trees) were selected within sampling plots. A total of 35 predictors were measured over different scales, including 25 remote sensing indices of forest conditions, climate and air pollutants. Structural Equation Models were used to test the causal linkages of predictors with lichens, distinguishing functional categories (size, growth and reproductive strategy). A total of 69 lichen species were recorded. Cavity trees and logs supported the largest diversity, while snags and healthy trees had the lowest diversity. Functional lichen groups responded differently to fine-scale variables, including the diameter, height, density and pH of trees. Air pollutants affected species with sexual and mixed strategies. Lichens were sensitive to precipitation, temperature and wind speed, with foliose and sexual species responding positively to the latter. The abundance of all species and macrolichens increased with tree senescence and decreased with canopy continuity. Lichens occupying snags and logs responded negatively to primary productivity and tree senescence, but positively to soil organic matter. Our findings suggest: i) the functional structure of lichen communities varies non-linearly with the wood decay process; ii) the reproductive strategy influences the sensitivity to air pollutants, iii) climate variables influence dispersal and colonization of woody substrates; and iv) forest structure/succession interacts with tree decay.

Can Chitin and Chitosan Replace the Lichen Evernia prunastri for Environmental Biomonitoring of Cu and Zn Air Contamination?

This study compared the ability of the lichen Evernia prunastri, chitin and chitosan to take up Cu²⁺ and Zn²⁺. It was hypothesized that chitin and chitosan have an accumulation capacity comparable to the lichen, so that these biopolymers could replace the use of E. prunastri for effective biomonitoring of Cu and Zn air pollution. Samples of the lichen E. prunastri, as well as chitin (from shrimps) and chitosan (from crabs), were incubated with Cu and Zn solutions at concentrations of 0 (control), 10, 25, 50, 75, and 100 µM and analyzed by Inductively Coupled Plasma Mass Spectrometry (ICP-MS). Metal concentrations accumulated by lichen, chitin and chitosan samples were strongly and linearly correlated with the concentrations in the treatment solutions. The lichen always showed significantly higher accumulation values compared to chitin and chitosan, which showed similar accumulation features. The outcomes of this study confirmed the great effectiveness of the lichen Evernia prunastri for environmental biomonitoring and showed that chitin and chitosan have a lower accumulation capacity, thus suggesting that although these biopolymers have the potential for replacing E. prunastri in polluted areas, their suitability may be limited in areas with intermediate or low pollution levels.

Insight into the pattern of heavy-metal accumulation in lichen thalli

BACKGROUND

Heavy metals that pass through the plasmalemma are expected to influence on lichen metabolic processes; however, lichens may tolerate high concentrations of metals by sequestrating them extracellularly. Heavy metal accumulation level fundamentally determine the success of lichens in the colonisation of polluted sites; however, the proportions between extra- and intracellular metal concentrations in lichen thalli are still poorly recognized. In this study metal accumulation patterns of selected toxic trace elements, i.e. Pb, Cd, and micronutrients, i.e. Zn, Cu and Ni, in Cladonia cariosa thalli were recognised in relation to extra- and intracellular fractions.

METHODS

The intracellular and total concentrations of Zn, Pb, Cd, Cu and Ni in lichen thalli collected from eleven variously polluted sites were determined by means of atomic absorption spectrometry. Additionally, organic carbon and total nitrogen contents as well as pH of soil substrate were measured.

RESULTS

The accumulation patterns differed between studied metal elements; the major part of Zn, Pb and Cd loads was accumulated extracellularly, whereas Cu and Ni accumulation was mostly intracellular. Like toxic trace elements, Zn was accumulated mainly extracellularly at high polluted sites. The non-linear models most reliably reflect relationships between intracellular and extracellular metal contents in C. cariosa thalli. The intracellular contents of Zn, Pb, Cd and Cu increased slower at higher than at lower extracellular concentrations. Moreover, at higher total concentrations of elements in the thalli, their extracellular proportions were markedly increased.

CONCLUSION

The results suggest that in the face of extreme Zn-enrichment, lichens demonstrate the ability to accumulate the excess of Zn outside the cells. Therefore, it can be concluded that metal accumulation depend not only on the element but also on its abundance in the environment and direct availability for lichens. The studied species showed a defence against excessive intracellular accumulation when a given element is in excess. Such capability may facilitate the colonization of extremely polluted sites by certain pioneer lichens.

Enhanced denitrification performance of Alcaligenes sp. TB by Pd stimulating to produce membrane adaptation mechanism coupled with nanoscale zero-valent iron

The microbial reduction of nitrate in the presence of nanoscale zero-valent iron (nZVI) was evaluated to assess the feasibility of employing nZVI for biological denitrification treatment. The effect of modified nZVI on the growth, metabolism, and denitrification performance of Alcaligenes sp. TB under aerobic conditions was studied. Results showed that Alcaligenes sp. TB with nZVI/Pd had 31.5% increase in nitrate removal and 18.1% decrease in nitrite accumulation within 28 h. nZVI/Pd exhibited less inhibition on the cell growth (OD₆₀₀ = 0.725), NADH/NAD⁺ ratio (86% of control), and electron transfer system activity (68.5% of control). In addition, nZVI/Pd decreased the membrane fluidity by increasing the trans/cis isomerization ratio (317.7% of control) to enhance the resistance of nZVI. This study underlines the effects of nZVI/Pd on membrane susceptibility via membrane fatty acid transformation during denitrification and suggests the influence of engineered nanomaterials on denitrification.

Exploration of an Extracellular Polymeric Substance from Earthworm Gut Bacterium (Bacillus licheniformis) for Bioflocculation and Heavy Metal Removal Potential

The present study shows the potential of an extracellular polymeric substance (EPS) produced by Bacillus licheniformis strain KX657843 isolated from earthworm (Metaphire posthuma) gut in the sorption of Cu(II) and Zn(II) and in flocculation. After harvesting bacterial cells from sucrose supplemented denitrifying culture medium, the EPS was extracted following ethanolic extraction method. The Fourier Transform Infrared Spectroscopy (FTIR) and 1H and 13C Nuclear Magnetic Resonance (NMR) of EPS revealed its functional groups, electronegative constituents, unsaturated carbon, and carbonyl groups. The negatively charged functional groups of carbohydrates and protein moiety of the EPS endowed it with heavy metal binding capacity through electrostatic interactions. The highest flocculation activity (83%) of EPS was observed at 4 mg L−1 and pH 11. The metal sorption by EPS increased with increasing pH. At pH 8, the EPS was able to remove 86 and 81% Cu(II) and Zn(II), respectively, from a 25 mg L−1 metal solution. 94.8% of both the metals at 25 mg L−1 metal solutions were removed by EPS at EPS concentration of 100 mg L−1. From Langmuir isotherm model, the maximum sorption capacities of EPS were calculated to be 58.82 mg g−1 for Cu(II) and 52.45 mg g−1 for Zn(II). The bacterial EPS showed encouraging flocculating and metal sorption properties. The potential to remove Cu(II) and Zn(II) implies that the EPS obtained from the earthworm gut bacteria can be used as an effective agent for environmental remediation of heavy metals and in bioflocculation.