Phytoremediation of a multi contaminated soil: mercury and arsenic phytoextraction assisted by mobilizing agent and plant growth promoting bacteria

Purpose

The possibility of using chemical and microbial additives to enhance the phytoextraction of mercury (Hg) and arsenic (As) from a multi-contaminated soil could be very effective, leading to a significant saving in terms of time and costs of the reclamation. The aim of this study was to evaluate the efficacy of the addition of (i) thiosulfate and (ii) metal-tolerant bacteria isolated from the polluted soil having plant growth promotion (PGP) potential to perform As and Hg phytoextraction by Brassica juncea and Lupinus albus.

Materials and methods

A collection of 13 bacterial isolates able to tolerate As and Hg was obtained from the contaminated soil, identified by partial 16S rRNA gene sequencing and tested in vitro for PGP activities. The most promising strains were further tested in vivo for the evaluation of plant growth ability and rhizocompetence on model plants. Pot experiments were conducted in microcosms, with polluted soil vegetated with B. juncea and L. albus. Ammonium thiosulfate and potassium dihydrogen phosphate were used as mobilizing agents, together with a bacterial consortium composed by the most promising PGP isolates.

Results and discussion

Thirteen indigenous metal-tolerant bacterial strains were isolated, and their in vitro characterization highlighted their great potential in assisting the phytoremediation process; most of them tolerated both trace elements and showed, at the same time, multiple PGP traits. The results were confirmed in vivo on model plants and lead to the selection of the most promising PGP strains to be applied in microcosm-scale phytoextraction experiments. Thiosulfate addition significantly increased the mobilization of both elements, promoting bioavailability and phytoextraction. When a selected bacterial consortium was supplemented in addition to thiosulfate, the efficacy of the phytoaccumulation was increased up to 85 % for As and up to 45 % for Hg.

Conclusions

The use of the common fertilizer thiosulfate appeared to have great potential in phytoextraction practices since it was able to facilitate the uptake by plants of both Hg and As. Moreover, the application of a consortium of indigenous PGP bacteria (PGPB) produced a further positive effect on the plant biomass, supporting and enhancing the phytoextraction strategy, thus demonstrating their potential in a microbe-assisted phytoremediation intervention.

     

Effect of Long-Term Soil Management on the Mutual Interaction Among Soil Organic Matter, Microbial Activity and Aggregate Stability in a Vineyard

Vineyard management practices to enhance soil conservation principally focus on increasing carbon (C) input, whereas mitigating impacts of disturbance through reduced tillage has been rarely considered. Furthermore, information is lacking on the effects of soil management practices adopted in the under-vine zone on soil conservation. In this work, we evaluated the long-term effects (22 years) of alley with a sown cover crop and no-tillage (S + NT), alley with a sown cover crop and tillage (S + T), and under-vine zone with no vegetation and tillage (UV) on soil organic matter (SOM), microbial activity, aggregate stability, and their mutual interactions in a California vineyard in USA. Vegetation biomass, microbial biomass and activity, organic C and nitrogen (N) pools, and SOM size fractionation and aggregate stability were analysed. Soil characteristics only partially reflected the differences in vegetation biomass input. Organic C and N pools and microbial biomass/activity in S + NT were higher than those in S + T, while the values in UV were intermediate between the other two treatments. Furthermore, S + NT also exhibited higher particulate organic matter C in soil. No differences were found in POM C between S + T and UV, but the POM fraction in S + T was characterized by fresher material. Aggregate stability was decreased in the order: S + NT > UV > S + T. Tillage, even if shallow and performed infrequently, had a negative effect on organic C and N pools and aggregate stability. Consequently, the combination of a sown cover crop and reduced tillage still limited SOM accumulation and reduced aggregate stability in the surface soil layer of vineyards, suggesting relatively lower resistance of soils to erosion compared to no-till systems.     

Computed tomographic diagnosis of a fracture of the floor of the pelvis in a Thoroughbred foal

This case report describes the clinical and diagnostic imaging findings, treatment and outcomes of a 15-day-old Thoroughbred foal referred for the evaluation of severe left hindlimb lameness of 8 days' duration. Radiographic examination of the left hindlimb and transcutaneous ultrasonographic examination of the pelvis were unremarkable. A computed tomographic (CT) examination was performed to investigate the proximal aspect of the limb and the pelvis; CT scans of the thorax were also acquired. In this case, CT images allowed detection of a closed, slightly displaced, oblique wedge-like fracture of the left caudal ramus of the pubis and medial ramus of the ischium, allowing an accurate diagnosis to guide appropriate treatment and prognostication. The foal was treated with anti-inflammatory drugs and box-rest. A follow-up by telephone interview with the trainer 3 years later revealed that the horse is in full athletic activity without any residual gait alteration related to the pelvic fracture.     

The plant alkaloid sanguinarine is a potential inhibitor of follicular angiogenesis

Sanguinarine (SA), a phytobiotic from Sanguinaria Canadensis, has been demonstrated to inhibit vessel growth. Current restrictions on the use of antibiotic growth promoters have motivated addition of this alkaloid as a naturally appetizing feed additive for farm animals. However, concern may araise since angiogenesis is a fundamental event in ovarian follicle growth. Therefore, the aim of this study was to evaluate the potential negative role of SA in follicular angiogenesis. For this purpose, we studied the effect of 300 nM SA on the production of vascular endothelial growth factor (VEGF) by swine granulosa cells from follicles >5 mm and on the activation of Akt, the main effector of the VEGF signalling pathway. In addition, the potential interference of SA in vessel development was tested in an in vitro angiogenesis bioassay. SA inhibited both VEGF production and VEGF-induced Akt activation in swine granulosa cells. Moreover, it was able to block vessel growth induced by VEGF. Taken together, our results suggest that SA could be detrimental to follicular angiogenesis, and therefore supplementation of feed with this alkaloid should be carefully considered.     

Relative Importance of Mineralogy and Organic Matter Characteristics on Macroaggregate and Colloid Dynamics in MG‐Silicate Dominated Soils

Soil aggregation and organic matter (OM) conservation are important in the prevention of land degradation. Aggregation processes and OM turnover influence each other and depend on the characteristics of both minerals and organic pools. We assessed the relative importance of the organic and mineral phases at the macroaggregate and colloidal scale in two soils (CHL and SRP, chlorite and serpentine‐rich, respectively) where Mg‐silicates dominated, by incubating them with a relatively degraded and oxidized organic fraction, that is the humic acids (HAs) extracted from the organic horizons of both CHL and SRP. The HA from SRP were more aromatic and richer in phenolic groups, whereas HA from CHL were N‐richer, more aliphatic and richer in carboxyl groups. The SRP soil formed larger amounts of macroaggregates, more stable than in CHL. At the colloidal scale, SRP was more flocculated and clay had a lower electrophoretic mobility than CHL. HA enhanced aggregate formation in both samples but improved aggregate stability only in CHL. In CHL, slight differences in electrophoretic mobility were visible, while in SRP, differences were more pronounced, with a point of zero charge at lower pH and larger hydrodynamic diameter. The abundance of Mg in SRP may have favoured the formation of weaker outer‐sphere interactions and the release of clay‐HA associations upon water dispersion, while in CHL Ca formed more stable bonds with HA. In SRP, ligand exchange reactions can be ruled out, conversely to the dominant bonding mechanism occurring in Al‐silicate dominated soils, with important consequences on the release of OM‐loaded clay particles. Copyright © 2016 John Wiley & Sons, Ltd.     

Tissue distribution of the antigenic variants of canine parvovirus type 2 in dogs

Twelve dogs dead as consequence of natural infection caused by canine parvovirus (CPV) type 2a (n=4), type 2b (n=4) or type 2c (n=4) were investigated for determining the viral DNA loads in different tissue samples. By means of a real-time PCR assay, CPV DNA was detected in all tissues examined, with the highest titres observed in the lymphoid tissue and the lowest loads in the urinary tract. Surprisingly, the nervous tissue was found to contain considerable amounts of CPV nucleic acid. Similar patterns of tissue distribution were observed in all the examined dogs irrespective of the antigenic variant causing the disease.