Phytoremediation potential of forage mulberry (Morus atropurpurea Roxb.) for cadmium contaminated paddy soils.

Mulberry is an important material to utilize the Cd polluted farmland in China and planting forage mulberry is a new development direction. This study aimed to investigate the changes of annual biomass and Cd content in shoot of Guisangyou 62, Guisangyou 12 and Yuesang 11 in field XT-C1, XT-X1 and ZZ-M1 under the pressure of Cd in 3 years. The Cd extraction ability of forage mulberry was analyzed, and the safety of forage mulberry was also discussed. The results showed that the annual biomass of each forage mulberry shoot could reach 64.52 ∼ 86.61 t/hectare (ha). The total harvest biomass of Guisangyou 12 was the highest, followed by Guisangyou 62 and Yuesang 11. In the same test area, for different forage mulberry varieties, there were no significant differences in Cd content in the shoot at each sampling time, and the Cd concentrations in shoot were in the range of 0.05 ∼ 0.66 mg/kg, meeting the hygienical standard for feeds (GB 13078-2017, China). Without considering the test area, the average Cd removal amount of each forage mulberry in a year was about 18.52 g/ha. Planting forage mulberry may become a new ecological economic model to achieve the safe utilization of Cd polluted farmland.Novelty statement Mulberry is one of the most important plants for safe utilization the Cd polluted farmland in China and planting mulberry as animal feed is a new development direction. This study investigated the effects of Cd on the shoot biomass of 3 forage mulberry varieties at 3 experimental areas in 3 years. It also examined how much Cd could be removed from soil by harvesting forage mulberry for 4 times a year. The Cd content in the shoot of forage mulberry and its safety were also evaluated.

Accumulation of Cd by three forage mulberry (Morus atropurpurea Roxb.) cultivars in heavy metal-polluted farmland: a field experiment.

A 3-year field experiment was conducted to evaluate the accumulation ability of 3 forage mulberry (Morus atropurpurea Roxb.) varieties (Guisangyou 62, Guisangyou 12, Yuesang 11) for Cadmium (Cd). The results showed that the shoot biomass of forage mulberry could reach to 64.51~69.58 t/ha in 2018. The total production of Guisangyou 12 was the highest among the tested 3 cultivars in each year. However, the biomass of the 3 varieties displayed without significant differences at every sampling time. In addition, the concentrations of Cd in the roots of the 3 mulberry cultivars were higher than those in the corresponding shoots in 2018. But in 2019, the Cd content in roots was near to that of shoots. The Cd concentrations in the roots of the forage mulberry showed Guisangyou 62 > Yuesang 11 > Guisangyou 12. And the Cd concentrations in shoots of all the 3 tested forage mulberry varieties were less than 1 mg/kg, meeting the hygienical standard for feeds (China). Though the 3 forage mulberry varieties were not hyperaccumulators for Cd, they could be used as alternative plants to make use of the Cd-polluted (< 1.0 mg/kg) paddy soils.

The mobility of cadmium and lead in the soil-mulberry-silkworm system.

Evaluation of the transportation of heavy metals in food chain has received a great deal of attention. In this study, the mobility of cadmium (Cd) and lead (Pb) in soil-mulberry-silkworm system was assessed. The results showed that bioconcentration factors for Cd and Pb were lower than 1 for all the three mulberry cultivars. Higher translocation factors (TFs) were observed in the levels from branch to leaf, larvae to excrement. The BCFs of Pb in root and silkworm excrement were higher than those in the other parts. Meanwhile, most of Cd accumulated from soils located in the root (48.00-54.40%) and only about 10% was in the leaf. But the Cd and Pb had significant effects on the ratios of cocoon shell with Yuesang 11 under different planting densities. For Yuesang 11 and Qiangsang 1, the Pb percentages were roots > branches > leaves > stems. The rates of ingestion (IR) and digestion (DR) were a little higher than those in the control at first and then decreased gradually with time. The IR reached the lowest values on 8th day while the DR arrived at the highest. Planting mulberry and raising silkworm could be a reasonable method for the utilization of heavy metal contaminated paddy soils.

Subcellular distribution and chemical forms of cadmium in Morus alba L.

Morus alba L. (mulberry) is a perennial woody tree and a species with great potential for Cd phyremediation owing to its large biomass and extensive root system. The mechanisms involved in Cd detoxification were investigated by analyzing the subcellular distribution and chemical forms of Cd in mulberry in the present study. These results indicated that 53.27-70.17% of Cd mulberry accumulated was stored in the root and only about 10% were in the leaves. Lots of the Cd was located in the cell wall of the mulberry root and in soluble fraction of the mulberry leaf. Moreover, in roots, the largest amount of Cd was in the form of undissolved Cd-phosphate. While in mulberry leaves and stems, most of the Cd was extracted by 2% Acetic acid and 0.6 M HCl, representing Cd-phosphate and Cd-oxalate. It could be concluded that the Cd combination with peptides and organo-ligands in vacuole of leaf or complexed with proteins or cellulose in the cell wall of root might be contributed to the tolerance of mulberry to Cd stress. The mulberry could be used to remediate the Cd polluted farmland soils.

Adsorption of Cd(II) by rhizosphere and non-rhizosphere soil originating from mulberry field under laboratory condition.

In this study, the adsorption behavior of Cd ions by rhizosphere soil (RS) and non-rhizosphere soil (NS) originated from mulberry field was investigated. The Langmuir, Freundlich and the Dubinin-Radushkevich (D-R) equations were used to evaluate the type and efficiency of Cd adsorption. The RS was characterized by lower pH but the higher content of soil organic matter and cation exchange capacity (CEC) as compared to NS. Also, the maximum adsorption of Cd2+ for RS (5.87 mg/g) was slightly bigger than that for NS (5.36 mg/g). In Freundlich isotherm, the Kf of the adsorption of Cd2+ to surface of the RS components was higher than that of the NS, indicating stronger attraction between Cd2+ and components of the RS. According to the D-R model, the adsorption of Cd2+ by both soils was dominated by ion exchange phenomena. These results indicated that mulberry roots modified physical and chemical properties of the RS under field conditions, which also affected the Cd sorption efficiency by soil components during laboratory experiments. Current knowledge of the Cd2+ sorption processes in the rhizosphere of mulberry may be important if these trees are planted for use in phytoremediation of Cd contaminated soils.

Effect of low-concentration rhamnolipid biosurfactant on Pseudomonas aeruginosa transport in natural porous media.

The effect of low-concentrations of monorhamnolipid biosurfactant on transport of Pseudomonas aeruginosa ATCC 9027 in natural porous media (silica sand and a sandy soil) was studied with miscible-displacement experiments using artificial groundwater as the background solution. Transport of two types of cells was investigated, glucose- and hexadecane-grown cells with lower and higher cell surface hydrophobicity (CSH), respectively. The effect of hexadecane presence as a residual non-aqueous phase liquid (NAPLs) on transport was also examined. A clean-bed colloid deposition model was used to calculate deposition rate coefficients (k) for quantitative assessment. Significant cell retention was observed in the sand (81% and 82% for glucose- and hexadecane-grown cells, respectively). Addition of a low-concentration rhamnolipid solution enhanced cell transport, with 40 mg/L of rhamnolipid reducing retention to 50% and 60% for glucose- and hexadecane-grown cells, respectively. The k values for both glucose- and hexadecane-grown cells correlate linearly with rhamnolipid-dependent CSH represented as bacterial-adhesion-to-hydrocarbon rate of cells. Retention of cells by the soil was nearly complete (>99%). Addition of 40 mg/L rhamnolipid solution reduced retention to 95%. The presence of NAPLs in the sand increased the retention of hexadecane-grown cells with higher CSH. Transport of cells in the presence of the NAPL was enhanced by rhamnolipid at all concentrations tested, and the relative enhancement was greater than in was in the absence of NAPL. This study shows the importance of hydrophobic interaction on bacterial transport in natural porous media and the potential of using low-concentration rhamnolipid for facilitating the transport in subsurface for bioaugmentation efforts.

Transport of bacteria in porous media and its enhancement by surfactants for bioaugmentation: A review.

The success of bioaugmentation processes for groundwater bioremediation requires efficient transport of bacteria in the subsurface environment. In this paper, the factors that influence transport of bacterial cells in porous media are reviewed and the effects of surfactants on the transport are discussed. Movement of bacterial cells in porous media is a process driven by advection and hydrodynamic dispersion forces of fluids. Immobilization of bacterial cells takes place due to processes such as adsorption and straining. Blocking and ripening along with bacterial migration process decrease and increase the retention of cells in porous media, respectively. Physicochemical properties of the porous media, groundwater chemistry, and properties of the bacterial cells affect the transport behavior. Surfactants have the potential to modify bacterial surface properties for both bacterial cells and medium solids, and thus enhance bacterial transport.

Effect of low-concentration rhamnolipid on transport of Pseudomonas aeruginosa ATCC 9027 in an ideal porous medium with hydrophilic or hydrophobic surfaces.

The success of effective bioaugmentation processes for remediation of soil and groundwater contamination requires effective transport of the injected microorganisms in the subsurface environment. In this study, the effect of low concentrations of monorhamnolipid biosurfactant solutions on transport of Pseudomonas aeruginosa in an ideal porous medium (glass beads) with hydrophilic or hydrophobic surfaces was investigated by conducting miscible-displacement experiments. Transport behavior was examined for both glucose-grown and hexadecane-grown cells, with low and high surface hydrophobicity, respectively. A clean-bed colloid deposition model was used for determination of deposition rate coefficients. Results show that cells with high surface hydrophobicity exhibit greater retention than cells with low surface hydrophobicity. Rhamnolipid affects cell transport primarily by changing cell surface hydrophobicity, with an additional minor effect by increasing solution ionic strength. There is a good linear relation between k and rhamnolipid-regulated cell surface hydrophobicity presented as bacterial-adhesion-to-hydrocarbon (BATH) rate of cells (R(2)=0.71). The results of this study show the importance of hydrophobic interaction for transport of bacterial cells in silica-based porous media, and the potential of using low-concentration rhamnolipid solutions for facilitating bacterial transport in bioaugmentation efforts.

Characteristics of mannosylerythritol lipids and their environmental potential.

Mannosylerythritol lipids (MELs) are promising biosurfactants containing two glycosyl derivatives and various fatty acids, which are mainly secreted by Pseudozyma as well as Ustilago. In this review, the latest research is demonstrated on production conditions, structural diversity, self-assembling properties and versatile biochemical functions of MELs. The genetic study and synthetic pathways, which mainly influence the type and yield of MELs production. Due to the excellent surface activity, biocompatibility and restorative function, MELs can be used in enviornmental industry, which has not been widely noted. In this paper, the current status of research on enviornmental potential of MELs has been discussed including petroleum degradation, bioconversion of chemical wastes and enhanced bioremediation of amphiphilic wastes.

Effect of low-concentration rhamnolipid on adsorption of Pseudomonas aeruginosa ATCC 9027 on hydrophilic and hydrophobic surfaces.

The effects of low-concentration monorhamnolipid (monoRL) on the adsorption of Pseudomonas aeruginosa ATCC 9027 grown on glucose or hexadecane to glass beads with hydrophobic or hydrophilic surfaces was investigated using batch adsorption experiments. Results showed that adsorption isotherms of the cells on both types of glass beads fitted the Freundlich equation better than the Langmuir equation. The Kf of the Freundlich equation for adsorption of hexadecane-grown cell to glass beads with hydrophobic surface was remarkably higher than that for adsorption of hexadecane-grown cell to glass beads with hydrophilic surface, or glucose-grown cell to glass beads with either hydrophilic or hydrophobic surface. Furthermore, it decreased with the increasing monoRL concentration. For both groups of cells, the zeta potential was close to each other and stable with the increase of monoRL concentration. The surface hydrophobicity of hexadecane-grown cells, however, was significantly higher than that of the glucose-grown cells and it decreased with the increase of monoRL concentration. The results indicate the importance of hydrophobic interaction on adsorption of bacterial cells to surfaces and monoRL plays a role in reducing the bacterial adsorption by affecting cell surface hydrophobicity.

Role of low-concentration monorhamnolipid in cell surface hydrophobicity of Pseudomonas aeruginosa: adsorption or lipopolysaccharide content variation.

A role of rhamnolipid biosurfactant to enhance the biodegradation of hydrocarbons is known to be enhancing bacterial cell surface hydrophobicity (CSH) and adhesion of cells to hydrocarbons. Assumptions regarding the mechanism for rhamnolipid in changing CSH of Gram-negative bacteria are rhamnolipid-induced release of lipopolysaccharide (LPS) from the cell's outer membrane and adsorption/orientation of rhamnolipid on the cell surface. In this study, the relation between cell-wall LPS or rhamnolipid content and CSH of a Pseudomonas aeruginosa bacterium subjected to rhamnolipid treatment was investigated to add insights to the mechanism. Results showed that the initial CSH was determined by the type of substrate the cells grow on and the stage of growth. For glucose-grown cells with low initial CSH and high LPS content, rhamnolipid sorption in cell wall had no discernable effect on CSH. For cells grown on glycerol with medium initial CSH and low LPS content, rhamnolipid sorption increased CSH of exponential-phase cells but decreased that of stationary-phase cells. For hexadecane-grown cells with high initial CSH and high LPS content, rhamnolipid sorption decreased CSH of both exponential-phase and stationary-phase cells. The results indicated that CSH has a better correlation to the content of rhamnolipid in the cell wall than to the content of LPS in the presence of rhamnolipid treatment and that rhamnolipid adsorption may be an important mechanism for rhamnolipid to alter CSH of P. aeruginosa.

[Purification and characterization of the biosurfactant rhamnolipid].

Biosurfactant rhamnolipid is a metabolic intermediate produced by microorganisms under a certain condition. There are the polar hydrophilic group and the non-polar hydrophobic group in rhamnolipid molecule which always exhibits high surface or interfacial activity. A reliable separation and purification method as well as component identification technique is essential for success of production process. The rhamnolipid was produced by aerobic fermentation using Pseudomonas aeruginosa CCTCC AB93066 in this study. It was separated from the culture by acid precipitation and purified by column chromatography until two groups of monorhamnolipid and dirhamnolipid were obtained. High performance liquid chromatography with mass spectrometry (HPLC-MS) examination showed that either the monorhamnolipid or the dirhamnolipid contained three major species. They were RhaC10C10, RhaC10C12-H2, RhaC10C12 for monorhamnolipid and Rha2C10 C10, Rha2C10 C12-H2, Rha2 C10 C12 for dirhamnolipid. The results of the study suggested that Pseudomonas aeruginosa CCTCC AB93066 is a good strain for rhamnolipid production. Acid precipitation-column chromatography technique is good for purification of rhamnolipid. Meanwhile, HPLC-MS is a reliable method for identifying components of rhamnolipid with high sensitivity and accuracy.