Digestion of duckweed (Lemna spp.) by the grass carp (Ctenopharyngodon idella)

A feeding trial was conducted in 55-1 aquaria indoors with the grass carp ( Ctenopharyngodon idella Val.) using fresh duckweed ( Lemna spp.) as food. Faeces dry weight was closely correlated with dry weight of duckweed consumed based upon a linear regression. From this regression, the estimated true digestibility of dry matter was 65%. Samples of duckweed and fish faeces were analysed for crude protein and gross energy. Van Soest's Analysis was conducted on composite samples of duckweed and faeces. Apparent digestibilities were 80% for crude protein, 61% for gross energy, 72% for organic cell contents, and 30% for organic cell wall constituents.     

Growing duckweed in swine wastewater for nutrient recovery and biomass production

Spirodela oligorrhiza, a promising duckweed identified in previous studies, was examined under different cropping conditions for nutrient recovery from swine wastewater and biomass production. To prevent algae bloom during the start-up of a duckweed system, inoculating 60% of the water surface with duckweed fronds was required. In the growing season, the duckweed system was capable of removing 83.7% and 89.4% of total nitrogen (TN) and total phosphorus (TP) respectively from 6% swine lagoon water in eight weeks at a harvest frequency of twice a week. The total biomass harvested was 5.30 times that of the starting amount. In winter, nutrients could still be substantially removed in spite of the limited duckweed growth, which was probably attributed to the improved protein accumulation of duckweed plants and the nutrient uptake by the attached biofilm (algae and bacteria) on duckweed and walls of the system.     

Multifaceted roles of duckweed in aquatic phytoremediation and bioproducts synthesis

Duckweed (Lemnaceae) is a fast‐growing aquatic vascular plant. It has drawn an increasing attention worldwide due to its application in value‐added nutritional products and in sewage disposal. In particular, duckweed is a promising feedstock for bioenergy production. In this review, we summarized applications of duckweed from the following four aspects. Firstly, duckweed could utilize nitrogen, phosphorus, and inorganic nutrition in wastewater and reduces water eutrophication efficiently. During these processes, microorganisms play an important role in promoting duckweed growth and improving its tolerance to stresses. We also introduced our pilot‐scale test using duckweed for wastewater treatment and biomass production simultaneously. Secondly, its capability of fast accumulation of large amounts of starch makes duckweed a promising bioenergy feedstock, catering the currently increasing demand for bioethanol production. Pretreatment conditions prior to fermentation can be optimized to improve the conversion efficiency from starch to bioethanol. Furthermore, duckweed serves as an ideal source for food supply or animal feed because the composition of amino acids in duckweed is similar to that of whey protein, which is easily digested and assimilated by human and other animals. Finally, severing as a natural plant factory, duckweed has shown great potential in the production of pharmaceuticals and dietary supplements. With the surge of omics data and the development of Clustered Regularly Interspaced Short Palindromic Repeats technology, remodeling of the metabolic pathway in duckweed for synthetic biology study will be attainable in the future.     

Nutrient recovery from swine lagoon water by Spirodela punctata.

Spirodela punctata 7776, the best duckweed strain in total protein production selected from in vitro screening experiments with synthetic swine lagoon water medium was examined for N and P recovery. It has shown a capability to grow in and to remove N and P from synthetic swine lagoon water with high N (240 mg NH4 N/l) and P (31.0 mg PO4 P/l) levels. A lag period of approximately 96 h was observed before the duckweed started to grow. During the lag period, utilization of N and P by the duckweed was very slow. The rates of N and P uptake, and duckweed growth increased with the increase of the initial N and P concentrations in the medium. The highest rates of N and P uptakes, and duckweed growth observed in this study were 0.955. 0.129 mg/l-h, and 1.33 g/m2-h (or 31.92 g/m2-day), respectively. The N:P ratio in swine lagoon water is adequate for growing the duckweed.     

Growth and energy budget in young grass carp, Ctenopharyngodon idella Val., fed plant and animal diets

Young grass carp held under laboratory conditions were fed either duckweed or tubificid worms. Food consumption ( C ), faecal production ( F ), excretion ( U ), metabolism ( R ) and growth ( G ) were estimated for fish fed both diets. Fish fed tubificid worms had higher growth rates than those fed duckweed, in terms of wet weight, dry matter, protein, lipid and energy. Fish fed duckweed consumed more wet and dry matter than did the fish fed tubificids, but rates of protein and lipid consumption were lower. The energy budget was estimated to be 100C = 9 F + 8 U + 61 R + 22 G for fish fed tubificids, and 100C = 35 F + 5 U + 51 R + 9 G for fish fed duckweed. Linear relationships existed between specific growth rate in wet weight and rate of food absorption (consumption minus faecal production) in dry matter, protein or energy. Food type did not have a significant effect on these relationships. It was concluded that differences in growth rate between grass carp fed different diets were mainly caused by differences in absorption rate.     

EFFECTS OF NUCLEIC ACID- AND PROTEIN-ANTIMETABOLITES ON FROND AND FLOWER PRODUCTION IN LEMNA GIBBA G3

Frond and flower production in a long-day duckweed, Lemna gibbaG3, grown under continuous illumination in the presence or absenceof varied concentrations of 5-fluorodeoxyuridine, 5-fluorouracill,2- thiouracil, 8-azaguanine or ethionine and/or correspondingmetabolite, i.e., thymidine, orotic acid, uracil, guanine ormethionine, have been investigated. From the results obtained,the presumptive flows of vegetative and reproductive informationfrom gene DNA to protein have been associated with frond andflower initiation in the duckweed meristem, respectively. (Received September 3, 1964; )     

Expression and characterization of Acidothermus cellulolyticus E1 endoglucanase in transgenic duckweed Lemna minor 8627

Endoglucanase E1 from Acidothermus cellulolyticus was expressed cytosolically under control of the cauliflower mosaic virus 35S promoter in transgenic duckweed, Lemna minor 8627 without any obvious observable phenotypic effects on morphology or rate of growth. The recombinant enzyme co-migrated with the purified catalytic domain fraction of the native E1 protein on western blot analysis, revealing that the cellulose-binding domain was cleaved near or in the linker region. The duckweed-expressed enzyme was biologically active and the expression level was up to 0.24% of total soluble protein. The endoglucanase activity with carboxymethylcellulose averaged 0.2 units mg protein(-1) extracted from fresh duckweed. The optimal temperature and pH for E1 enzyme activity were about 80 degrees C and pH 5, respectively. While extraction with HEPES (N-[2-hydroxyethyl]piperazine-N'-[2-ethanesulfonic acid]) buffer (pH 8) resulted in the highest recovery of total soluble proteins and E1 enzyme, extraction with citrate buffer (pH 4.8) at 65 degrees C enriched relative amounts of E1 enzyme in the extract. This study demonstrates that duckweed may offer new options for the expression of cellulolytic enzymes in transgenic plants.     

The effect of a duckweed cover on sulphide volatilisation from waste stabilisation ponds

The effects of a duckweed (DW) cover on the surface of waste stabilisation ponds on sulphide emissions were studied in a laboratory scale set-up of an anaerobic pond-reactor, followed by two algae (A) pond-reactors and two duckweed (Lemna gibba) pond-reactors. The concentrations of various S-components were measured at different depth in the reactors, while sulphide emissions were measured at the surface. Presence of a duckweed cover on the anaerobic pond-reactor resulted in a reduction of 99% in sulphide emission. In algae pond-reactors, sulphide emissions were negligible through chemical and biological conversion of sulphide. In the duckweed pond-reactors, colourless sulphur bacteria (Beggiatoa sp.) were observed on the duckweed roots. Batch tests showed that both micro-biological and possibly chemical oxidation occurred in a typical duckweed pond environment. The duckweed cover reduced H₂S volatilisation via two mechanisms, by forming a physical barrier and by providing attachment area for sulphide oxidising bacteria.     

Wastewater-grown duckweed may be safely used as fish feed

Duckweed has been used for the treatment of wastewater and as fish feed. A comparative study was carried out to determine (i) the efficacy of duckweed in treating hospital-based wastewater and (ii) the level of the microbial contamination of fish fed on wastewater-grown duckweed. There were two groups of ponds where fish farming was done. In one group of ponds (control ponds), duckweed that was grown using artificial fertilizer was used as fish feed; in another group (study ponds), wastewater-grown duckweed was used as fish feed. The faecal contamination of water, duckweed, and fish from study and control ponds were monitored by faecal coliform estimation. The presence of enteric pathogens among handlers, water, duckweed, and fish samples was also examined. It was observed that the faecal coliform counts of raw wastewater were 4.7 Log10 CFU/mL, which was reduced to <1 Log10 CFU/mL after treating with duckweed. There was no significant difference (P > 0.05) in faecal coliform counts in water collected from duckweed ponds and fish ponds of study and control areas. The wastewater-grown duckweed did not pose any health hazard to the handlers. These results demonstrated that the wastewater-treated duckweed may be safely used as fish feed.     

Effects of copper and cadmium on heavy metal polluted waterbody restoration by duckweed (Lemna minor).

Aquatic plants have been identified as a potentially useful group for accumulating and bioconcentrating heavy metals. In the study, we investigated changes in the contents of soluble protein and photosynthetic pigments as well as the activity of antioxidant enzymes caused by copper sulfate and cadmium dichloride, respectively in duckweed (Lemna minor) during concentration-dependent exposure (0.05-20 mg l(-1)) to metal salt. The results demonstrated that exposure to high concentration heavy metals (Cu>10 mg l(-1), Cd>0.5 mg l(-1)) could result the disintegration of antioxidant system in duckweed. Also, the significant decrease of contents of soluble protein and photosynthetic pigments was observed to high-level metal stress. Additionally, cadmium was found to be more toxic than copper on plants. The outcome of this study corroborate that Lemna minor is a suitable candidate for the phytoremediation of low-level copper and cadmium contaminated waterbody.     

Sensitivity of duckweed (Lemna major) to ultraviolet-B radiation

The sensitivity of an important aquatic macrophyte, duckweed (Lemna major), to UV-B radiation was studied under experimental conditions at three different doses designated as no, mild, and severe injury dose by observing visible injury symptoms and estimating levels of chlorophyll, pheophytin, carotenoids, protein, starch, free sugar, and peroxidase activity. Laboratory-grown duckweed plants were exposed to UV-B radiation at 0.4 mW/cm(2) intensity for different time periods. Mild and severe injury were developed at 6.48 and 8.64 J, respectively. Peroxidase activity increased at all the exposure levels. Dose-dependent decrease in chlorophyll and starch with drastic depletion in protein and free sugar content were observed. Pheophytin and carotenoids content increased at no injury level, but decreased at higher exposure level. The results indicate that ambient UV-B radiation at the indicated level acts as a physiological stress in Lemna major.     

Preference,performance, and impact of the water-lily aphid on multiple species of duckweed

1. The role of herbivores in driving the structure of freshwater macrophyte communities remains poorly understood in comparison with terrestrial ecosystems. For instance, although duckweed (subfamily Lemnoideae) are globally distributed, can be locally highly abundant and ecologically dominant, and are of growing economic importance, their interactions with herbivores remain understudied.
2. To address how herbivores may impact duckweed species composition, we here experimentally quantify the preference and performance of a common duckweed herbivore, the water-lily aphid (Rhopalosiphum nymphaeae) on four widespread duckweed species.
3. Our two-way choice experiments reveal that aphids display a preference for Spirodela polyrhiza > Landoltia punctata = Lemna minor > > Wolffia brasiliensis. These results are rarely influenced by natal host species.
4. By evaluating the growth of aphid populations on each duckweed species, we find that preference may be adaptive in certain ecological conditions.
5. Quantifying the population growth rate of duckweed growing in the presence and absence of aphids revealed differential tolerance of herbivory across duckweed species.
6. This study shows that aphids, through preferential feeding and significant differential effects on duckweed growth, can have a significant impact on duckweed population dynamics and potentially community composition.

     

pH及无机氮化合物对细脉浮萍生长的影响

研究以细脉浮萍 ( Lemna aequinoctialis)为研究对象 ,在完全培养液的基础上模拟生活污水的氨氮、硝酸氮浓度和 p H范围 ,研究了培养条件对其生长的影响。结果表明 ,这个浮萍种对 p H耐受的低限在 4～ 5之间 ,最适 p H范围为 5～ 6。非离子态的氨会对其生长产生抑制作用 ,在氨氮为唯一氮源的条件下 ,非离子态氨的浓度大于 0 .1 mg/L时会对此种的生长产生明显的抑制作用 ,接近 2 mg/L时 ,基本上致死。在研究的氨氮和硝酸氮浓度范围内 ( <40 mg N /L) ,铵根离子和硝酸根离子浓度增加可促进细脉浮萍的生长。氨氮中生长的植株过氧化物酶活性高于硝酸氮中的活性。     

Mapping of genes on the chloroplast DNA of Spirodela oligorhiza

With the use of spinach chloroplast RNAs as probes, we have mapped the rRNA genes and a number of protein genes on the chloroplast DNA (cpDNA) of the duckweed Spirodela oligorhiz. For a more precise mapping of these genes we had to extend the previously determined [14] restriction endonuclease map of the duckweed cpDNA with the cleavage sites for the restriction endonucleases Sma I and Bgl I. The physical map indicates that duckweed cpDNA contains two inverted repeat regions (18 Md) separated by two single copy regions with a size of 19 Md and 67 Md, respectively.By hybridization with spinach chloroplast rRNAs it could be shown that each of the two repeat units contains one set of rRNA genes in the order: 16S rRNA gene — spacer — 23S rRNA gene — 5S rRNA gene.A spinach chloroplast mRNA preparation (14S RNA), which is predominantly translated into a 32 Kilodalton (Kd) protein [9], hybridized strongly to a DNA fragment in the large single copy region, immediately outside one of the inverted repeats. With another mRNA preparation (18S), which mainly directs the in vitro synthesis of a 55 Kd protein [9], hybridization was observed with two DNA regions, located between 211° and 233° and between 137° and 170°, respectively. Finally, with a spinach chloroplast genomic probe for the large subunit of ribulose 1,5-bisphosphate carboxylase [17], hybridization was found with a DNA fragment located between 137° and 158° on the map.     

Sink trap: duckweed and dye attractant reduce mosquito populations

Duckweeds, such as Lemna minor Linnaeus (Alismatales: Lemnaceae), are common in aquatic habitats and have been suggested to reduce larval mosquito survivorship via mechanical and chemical effects. Furthermore, pond dyes are used increasingly in aquatic habitats to enhance their aesthetics, although they have been shown to attract mosquito oviposition. The present study examined the coupled effects of L. minor and black pond dye on the oviposition selectivity of Culex pipiens Linnaeus (Diptera: Culicidae) mosquitoes in a series of laboratory choice tests. Subsequently, using outdoor mesocosms, the combined influence of duckweed and pond dye on mosquito abundances in aquatic habitats was quantified. Mosquitoes were strongly attracted to duckweed, and oviposited significantly greater numbers of egg rafts in duckweed-treated water compared with untreated controls, even when the duckweed was ground. The presence of pond dye interacted with the duckweed and further enhanced positive selectivity towards duckweed-treated water. The presence of duckweed caused significant and sustained reductions in larval mosquito numbers, whereas the relative effects of dye were not evident. The use of floating aquatic plants such as duckweed, combined with dye, may help reduce mosquito populations via the establishment of population sinks, characterized by high rates of oviposition coupled with high levels of larval mortality.     

Growth characteristics of aquatic macrophytes cultured in nutrient-enriched water: II. Azolla,Duckweed, and Salvinia

Seasonal growth characteristics and biomass yield potential of 4 small-leaf, floating, aquatic macrophytes cultured in nutrient nonlimiting conditions were evaluated for central Florida’s climatic conditions. Biomass yields were found to be 10.6, 11.3, 16.1, and 32.1 t (dry wt) har^?1 yr^?1, respectively, for azolla (Azolla caroliniana), giant duckweed (Spirodela polyrhiza), common duckweed (Lemna minor), and salvinia (Salvinia rotundifolia). Operational plant density was in the range of 10–80 g dry wt m^?2 for azolla, 10–88 g dry wt m^?2 for giant duckweed, 10–120 g dry wt m^?2 for common duckweed, and 35–240 g dry wt m^?2 for salvinia. Specific growth rate (% increase per day) was maximum at low plant densities and decreased as the plant density increased. Results suggest that small-leaf, floating plants may not be suitable in monoculture biomass production systems because of low biomass yields, but they may be suitable for inclusion in poly culture systems with larger aquatic plants. The high N content (crude protein = 20–33%) of small-leaf,floating plants suggests the use of biomass as animal feed.     

贵州省浮萍形态学鉴定与遗传多样性分析

为调查贵州省浮萍种间亲缘关系及变异情况, 研究在贵州省辖9个地级行政区的多处水环境中共采集到 41份浮萍种质, 通过形态鉴定这些种质中33个属于绿萍属(Lemna), 6个属于紫萍属(Spirodela), 2个属于斑萍属/兰氏萍属(Landoltia)。利用叶绿体atpF-atpH间隔序列和rpS16内含子序列进行分子生物学分析和鉴定, 41份浮萍种质聚类到Lemna aequinoctialis、Lemna minor、Spirodela polyrhiza和Landoltia punctata 4个种。atpF-atpH间隔序列和rpS16内含子序列的单倍型多样性分别为0.98700和0.64700, 群体突变率分别为0.15380和0.14334, 平均每kb核苷酸差异数为47.20000和61.72200, 核苷酸多态性分别为0.08725和0.09158。研究讨论了中国亚热带温润季风地区浮萍的遗传多样性, 为浮萍亲缘关系分析提供了依据, 也为亚热带湿润季风气候地区植物的种属鉴定及资源化利用奠定了基础。     

Common Duckweed (Lemna minor) Is a Versatile High-Throughput Infection Model For the Burkholderia cepacia Complex and Other Pathogenic Bacteria

Members of the Burkholderia cepacia complex (Bcc) have emerged in recent decades as problematic pulmonary pathogens of cystic fibrosis (CF) patients, with severe infections progressing to acute necrotizing pneumonia and sepsis. This study presents evidence that Lemna minor (Common duckweed) is useful as a plant model for the Bcc infectious process, and has potential as a model system for bacterial pathogenesis in general. To investigate the relationship between Bcc virulence in duckweed and Galleria mellonella (Greater wax moth) larvae, a previously established Bcc infection model, a duckweed survival assay was developed and used to determine LD₅₀ values. A strong correlation (R² = 0.81) was found between the strains’ virulence ranks in the two infection models, suggesting conserved pathways in these vastly different hosts. To broaden the application of the duckweed model, enteropathogenic Escherichia coli (EPEC) and five isogenic mutants with previously established LD₅₀ values in the larval model were tested against duckweed, and a strong correlation (R² = 0.93) was found between their raw LD₅₀ values. Potential virulence factors in B. cenocepacia K56-2 were identified using a high-throughput screen against single duckweed plants. In addition to the previously characterized antifungal compound (AFC) cluster genes, several uncharacterized genes were discovered including a novel lysR regulator, a histidine biosynthesis gene hisG, and a gene located near the gene encoding the recently characterized virulence factor SuhB_Bc. Finally, to demonstrate the utility of this model in therapeutic applications, duckweed was rescued from Bcc infection by treating with bacteriophage at 6-h intervals. It was observed that phage application became ineffective at a timepoint that coincided with a sharp increase in bacterial invasion of plant tissue. These results indicate that common duckweed can serve as an effective infection model for the investigation of bacterial virulence factors and therapeutic strategies to combat them.     

Effects of artificial ultraviolet-B radiation on growth and fatty acid composition of duckweed (Lemna minor)

1. Duckweed (Lemna minor), collected either in summer or early fall was exposed under laboratory conditions to control (photosynthetically active and UV‐A radiation) or experimental (control plus UV‐B radiation) conditions. 2. Growth and survival were determined by counting the number of green, and brown/white fronds following 1–5 or 11 days of irradiation. Growth of duckweed was impaired by exposure to UV‐B radiation in the fall experiment but not in the summer. 3. Fatty acid compositions were analysed following 5 or 11 days of irradiation and a recovery period of 0, 5, 29 or 40 h. Concentrations of the major fatty acids, palmitic, linoleic (LA) and α‐linolenic (ALA) acids were similar in the summer and fall duckweed collections, but the summer samples had higher concentrations of the desaturation products of LA and ALA. 4. UV‐B exposure had small, but significant, and contrasting effects on duckweed fatty acid concentrations. In the summer experiment, duckweed exposed to UV‐B had slightly lower concentrations of major fatty acids than control duckweed, while the reverse was true in the fall experiments. 5. These minor effects of UV‐B on concentrations of LA and ALA would be unlikely to have a major impact on the supply of these essential fatty acids from duckweed to freshwater food webs.