Duckweed has been highlighted as an invaluable resource because of its abilities to remove nitrogen and phosphorus from wastewater coupling with the production of high starch/protein-containing plant ...biomass. Duckweed recruits microbes and particularly forms a stable “core” bacterial microbiota, which greatly reduces the colonization efficiency of plant growth-promoting bacteria (PGPB). In this study, natural duckweeds were enriched in a sterilized-partially treated wastewater effluent from a poultry farm. After 24 days of cultivation, the duckweed-associated bacteria (DAB) were isolated and evaluated for their plant growth-promoting (PGP) potentials by co-cultivation with axenic
Spirodela polyrhiza
. Ten species were found in more than one location and could be considered candidates for the stable “core” DAB. Among them, all isolates of
Acinetobacter soli, Acidovorax kalamii, Brevundimonas vesicularis, Pseudomonas toyotomiensis,
and
Shinella curvata
increased duckweed growth in Hoagland medium. The highest PGP ability was observed in
Sh. curvata
W12-8 (with EPG value of 208.72%), followed by
Paracoccus marcusii
W7-16 (171.31%),
Novosphingobium subterraneum
W5-13 (156.96%), and
Ac. kalamii
W7-18 (156.96%). However, the highest growth promotion in the wastewater was observed when co-cultured with W7-16, which was able to increase biomass dry weight and root length of duckweed by 3.17 and 2.26 folds, respectively.
Acetylcholine (ACh), an important neurotransmitter, plays a role in resistance to abiotic stress. However, the role of ACh during cadmium (Cd) resistance in duckweed (Lemna turionifera 5511) remains ...uncharacterized. In this study, the changes of endogenous ACh in duckweed under Cd stress has been investigated. Also, how exogenous ACh affects duckweed's ability to withstand Cd stress was studied. The ACh sensor transgenic duckweed (ACh 3.0) showed the ACh signal response under Cd stress. And ACh was wrapped and released in vesicles. Cd stress promoted ACh content in duckweed. The gene expression analysis showed an improved fatty acid metabolism and choline transport. Moreover, exogenous ACh addition enhanced Cd tolerance and decreased Cd accumulation in duckweed. ACh supplement reduced the root abscission rate, alleviated leaf etiolation, and improved chlorophyll fluorescence parameters under Cd stress. A modified calcium (Ca2+) flux and improved Cd2+ absorption were present in conjunction with it. Thus, we speculate that ACh could improve Cd resistance by promoting the uptake and accumulation of Cd, as well as the response of the Ca2+ signaling pathway. Also, plant-derived extracellular vesicles (PDEVs) were extracted during Cd stress. Therefore, these results provide new insights into the response of ACh during Cd stress.
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•Cd caused ACh response in vesicles, showed by ACh 3.0 transgenic duckweed.•Exogenous ACh alleviated Cd toxicity and enhanced photosynthesis in duckweed.•ACh promoted the accumulation of Cd with an enhanced expression of Cd transporters•ACh changed the Ca2+ flux and improved Cd absorption in duckweed.
The combined contamination of heavy metals and microplastics is widespread in freshwater environments. However, there are few researches on their combined effects on aquatic plants. In this study, ...the effects of single and combined stress of 0.01 mg L-1 cadmium (Cd), 50 mg L-1 polyethylene and 50 mg L-1 polypropylene for 15 days on the physiological response, ultrastructure and rhizosphere microbial community of duckweed were investigated. The results showed that Cd and microplastics single or combined stress inhibited the growth of duckweed, shortened the root length and decreased the chlorophyll content. Compared with single Cd treatments, the combination of microplastics and Cd increased duckweed growth rate and increased superoxide dismutase activity and malondialdehyde content and reduced chloroplast structural damage, indicating that the combined stress could reduce the toxicity of heavy metals to duckweed. Through the study of rhizosphere microbial diversity, 1381 Operational Taxonomic Unit (OTUs) were identified and rich microbial communities were detected in the duckweed rhizosphere. Among them, the main microbial communities were Proteobacteria, Bacteroidetes, and Cyanobacteria. Compared with Cd single stress, the ACE and chao index of rhizosphere microbial community increased under combined stress, indicating that the diversity and abundance of microbial communities were improved after combined stress treatment. Our study revealed the effects of heavy metals and microplastics on aquatic plants, providing a theoretical basis for duckweed applications in complex water pollution.
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•Combined stress of cadmium and microplastics can alleviate the toxic effect of cadmium on duckweed.•The diversity and abundance of microbial communities were improved after the combined stress treatment compared to Cd stress.•Rhizosphere microorganisms may improve growth and physiological metabolism of duckweed to reduce the toxic effect on duckweed
Duckweeds are small, rapidly growing aquatic flowering plants. Due to their ability for biomass production at high rates they represent promising candidates for biofuel feedstocks. Duckweeds are also ...excellent model organisms because they can be maintained in well-defined liquid media, usually reproduce asexually, and because genomic resources are becoming increasingly available. To demonstrate the utility of duckweed for integrated metabolic studies, we examined the metabolic adaptation of growing Lemna gibba cultures to different nutritional conditions. To establish a framework for quantitative metabolic research in duckweeds we derived a central carbon metabolism network model of Lemna gibba based on its draft genome. Lemna gibba fronds were grown with nitrate or glutamine as nitrogen source. The two conditions were compared by quantification of growth kinetics, metabolite levels, transcript abundance, as well as by .sup.13C-metabolic flux analysis. While growing with glutamine, the fronds grew 1.4 times faster and accumulated more protein and less cell wall components compared to plants grown on nitrate. Characterization of photomixotrophic growth by .sup.13C-metabolic flux analysis showed that, under both metabolic growth conditions, the Calvin-Benson-Bassham cycle and the oxidative pentose-phosphate pathway are highly active, creating a futile cycle with net ATP consumption. Depending on the nitrogen source, substantial reorganization of fluxes around the tricarboxylic acid cycle took place, leading to differential formation of the biosynthetic precursors of the Asp and Gln families of proteinogenic amino acids. Despite the substantial reorganization of fluxes around the tricarboxylic acid cycle, flux changes could largely not be associated with changes in transcripts. Through integrated analysis of growth rate, biomass composition, metabolite levels, and metabolic flux, we show that Lemna gibba is an excellent system for quantitative metabolic studies in plants. Our study showed that Lemna gibba adjusts to different nitrogen sources by reorganizing central metabolism. The observed disconnect between gene expression regulation and metabolism underscores the importance of metabolic flux analysis as a tool in such studies.
•Doxycycline was more toxic, than norfloxacin on tested aquatic organisms: plants and crustaceans.•The effect concentration (EC20) of doxycycline reduced by 20 % growth of L. minor was more than ...twice lower than for norfloxacin.•The leaf chlorophyll content was an early and sensitive indicator of the phytoxic effects of doxycycline in L. minor, before morphological changes were observed.•The effect concentration (EC20 in 180. min) of doxycycline immobilizing of daphnia by 20 % was almost twice lower as for norfloxacin.
The main reason for the appearance of pharmaceutical compounds in the aquatic environment is their regular excretion by humans and animals in an unchanged form or slightly metabolized. Pharmaceuticals limit the habitable living environment for aquatic organisms, because they can be toxic not only to bacteria but also to non-target organisms. Plants of the Lemnoideae subfamily and crustaceans Daphniindae family are widely used as bioindicators in freshwater environmental risk assessments. This study aimed to use biotests (Lemna test and Daphtoxkit) to determine the effect of two pharmaceuticals: antibiotic – Doxycycline (DOX) and semi-synthetic chemotherapeutic drug – Norfloxacin (NOR) on plants Lemna minor and crustaceans Daphnia magna. Standard Lemna test was extended to include pharmaceutical effects on plant chlorophyll content (LCC) and fluorescence (Fo, Fm, and Fv/Fm), and the confirmation of drug toxicity was the biotest Daphtoxkit assessing the immobilization (IM) of organisms. Studies have shown that DOX was more toxic than NOR on tested aquatic organisms: plants and crustaceans. The lowest observed effect concentration (EC20) of DOX and NOR reduced by 20 % LCC and Iy of L. minor was 2.14 and 8.11 mg × L−1, respectively. The LCC was an early and sensitive indicator of the phytotoxic effects of DOX in L. minor before morphological changes were observed. Confirmation of drug toxicity was the Daphtoxkit. The EC20 (180. min) of DOX and NOR, IM of daphnia by 20 % was 117.18 and 215.42 mg × L−1, respectively. In conclusion, DOX and NOR in aquatic environments may have significant implications for tested organisms and their ecosystems.
Duckweed-based ponds (DPs) are widely used to treat wastewater due to the rapid growth and high-value biomass of duckweed. However, their performance at nutrient removal is restricted by low ...dissolved oxygen (DO) concentrations in pond water, and direct aeration of a DP is impracticable because floating duckweed is vulnerable to interference by bubbles. Thus, we developed an influent pre-aeration treatment process for a DP and investigated its effect on the DO concentration and performance of the pilot-scale (12 m2) DP, as well as the underlying mechanism over a 9-month period. Pre-aeration increased the DO concentration (by 478 %) and oxidation reduction potential (by 55 %) in pond water, and promoted duckweed growth (by 33 %) and total phosphorous, total nitrogen, and NH4+-N removal (by 84 %, 80 %, and 91 %, respectively). It also increased the contributions of microorganisms to nitrogen and phosphorous removal (13.37 % and 35.52 % greater, respectively), indicating that it had greater beneficial effects on microorganisms than on duckweed. In the bacterial community, pre-aeration likely promoted nutrient removal by improving the growth and activity of bacterial assemblages involved in nutrient cycling (e.g., Rhodopseudomonas, Cloacibacterium, Candidatus_Limnoluna, and Novosphingobium in pond water), and by improving duckweed growth by altering the relative abundances of bacterial assemblages attached to duckweed. These findings help clarify the beneficial effects and mechanisms of influent pre-aeration, providing a new insight into the improvement and application of DPs.
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•Two duckweed ponds (with and without pre-aeration) were evaluated over 9 months.•Pre-aeration promoted duckweed growth (DG, by 33 %) and nutrient removal (NR, by 80 %).•Positive effect of pre-aeration on NR was greater by microorganism than by duckweed.•DG was promoted probably due to alterations of microorganisms attached to duckweed.
There is increasing concern about the effects of releasing emerging contaminants (i.e. endocrine-disrupting chemicals, pharmaceuticals, personal-care products and flame retardants) into the ...environment. Particular attention is being paid to perfluoroalkyl substances (PFAS) because of their persistence and bioaccumulation, especially in the aquatic environment. In this paper, we present results of a study aimed at evaluating the effects of different perfluorooctanoic acid (PFOA) concentrations (2, 20 and 200 μg/L) on morpho-physiological traits in Lemna minor L. plants. The accumulation of PFOA in the plant's tissues was also monitored. L. minor was selected as a model plant for ecotoxicological studies, and we performed a seven-day assay for this investigation. The results highlight the lack of inhibitory effects on biometric parameters such as mean frond area, total frond number, multiplication rate, doubling time of frond number and average specific growth rate, for each of tested PFOA concentrations. Also, at photosynthetic level, physiological measurements showed that chlorophyll content and electron transport rate (ETR) were not affected by the exposure to PFOA. Remarkably, the chlorophyll fluorescence images, used for the first time in a study on PFOA, evidenced no impairment to the photosynthetic efficiency, measured by the maximum quantum yield of photosystem II (PSII) photochemistry (Fv/Fm), the quantum efficiency of PSII photochemistry (ΦPSII) and the non-photochemical quenching (NPQ) over the leaf surface of PFOA-treated plants, in comparison to control. Quantification of PFOA in the growth medium at the end of the seven-day test revealed no statistically different concentrations in plates with or without L. minor plants. We detected increasing PFOA accumulation in plant tissues, in accordance with the PFOA concentrations in the medium. Therefore, the L. minor plants were capable of taking up and accumulating PFOA. The ecological impact of the environmentally relevant PFOA concentrations tested in this work on biological organisms of the aquatic environment is discussed.
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•Perfluoroalkyl substances (PFAS) represent an increasing concern for environment.•A 7-day test was used to evaluate the effects of PFOA to model plant Lemna minor.•Plant morpho-physiological traits were not affected by PFOA concentrations.•Plant PFOA accumulation was in relation to the PFOA levels in the growth medium.•Plant PFOA uptake is a concern for bioaugmentation effects in the aquatic ecosystem.
A highly simplified species for genome engineering would facilitate rational design of a synthetic plant. A candidate species is the aquatic, non-grass monocot wolffia (Wolffia australiana) in the ...Lemnaceae family. Commonly known as watermeal, wolffia is a rootless ball of several thousand cells the size of a pinhead and the fastest growing plant known on Earth. Its extreme morphological reduction is coupled to transposon-mediated streamlining of its transcriptome, which represents a core set of nonredundant protein coding genes. Despite its body plan and transcriptome being highly specialized for continuous growth, wolffia retains cell types relevant to higher plants. Finally, systems level studies with this species could enable the creation of a defined biological chassis for synthetic plant construction.
•Duckweeds contain 20–35% protein, 4–7% fat, 4–10% starch per dry weight.•Proteins constitute 4.8% Lys, 2.7% Met+Cys, and 7.7% Phe+Tyr.•48–71% of fat are polyunsaturated fatty acids, the n6/n3 ratio ...is 0.5 or less.•Mineral content can be easily manipulated by the composition of the nutrient medium.•Wolffia microscopica and Wolffiella hyalina are desirable as human food.
Duckweeds have been consumed as human food since long. Species of the duckweed genera, Spirodela, Landoltia, Lemna, Wolffiella and Wolffia were analysed for protein, fat, and starch contents as well as their amino acid and fatty acid distribution. Protein content spanned from 20% to 35%, fat from 4% to 7%, and starch from 4% to 10% per dry weight. Interestingly, the amino acid distributions are close to the WHO recommendations, having e.g. 4.8% Lys, 2.7% Met+Cys, and 7.7% Phe+Tyr. The content of polyunsaturated fatty acids was between 48 and 71% and the high content of n3 fatty acids resulted in a favourable n6/n3 ratio of 0.5 or less. The phytosterol content in the fastest growing angiosperm, W. microscopica, was 50mgg−1 lipid. However, the content of trace elements can be adjusted by cultivation conditions. Accordingly, W. hyalina and W. microscopica are recommended for human nutrition.
The increasing worldwide consumption of pharmaceuticals and personal care products such as ibuprofen (IBU) is leading to the widespread and persistent occurrence of these chemicals and their ...transformation products in soils and waters. Although at low concentrations, the continuous discharge of these micropollutants and the incomplete removal by the actual wastewater treatments can provoke accumulation in the environment with risks for the trophic chain. Non-target organisms as duckweed can be used for the environmental monitoring of pharmaceutical emerging contaminants. In this work, plants of Lemna gibba L. were exposed to high (0.20 and 1mgL−1) and environmentally relevant (0.02mgL−1) concentrations of IBU to investigate their removal and metabolization capacity. The main oxidized IBU metabolites in humans (hydroxy-IBU and carboxy-IBU) were determined in the intact plants and in the growth solutions, together with non-destructive physiological parameters and phytotoxic indicators. The IBU uptake increased with the increasing of IBU concentration in the medium, but the relative accumulation of the pharmaceutical and generation of hydroxy-IBU was higher in presence of the lower IBU treatments. Carboxy-IBU was not found in the plant tissue and solutions. The changes observed in growth and photosynthetic performances were not able to induce phyto-toxic effects. Apart from a mean physical-chemical degradation of 8.2%, the IBU removal by plants was highly efficient (89–92.5%) in all the conditions tested, highlighting the role of L. gibba in the biodegradation of emerging contaminants.
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•Lemna gibba L. was exposed to high and environmental levels of ibuprofen (IBU).•No phyto-toxic effects were observed through growth and physiological parameters.•The main oxidized IBU metabolites were determined in intact plants and growth medium.•The relative IBU uptake and metabolization ability occurred at the lower IBU levels.•A remarkable IBU removal from water was observed in all the IBU treatments.
