Abstract
The production of engineered nanoparticles (ENPs) has rapidly increased due to their wide range of applications in the field of electronics, medicine, chemistry and biology. Consequently, concerns have risen about the environmental release and potential negative impact of NPs. A few reports have described the effects of TiO2 NPs and quantum dots upon nitrogen fixing bacteria. However, the understanding of the interaction of NPs in plant-microbe interface (symbiotic association), like alfalfa (Medicago sativa L.)-Sinorhizobium meliloti, is still in its infancy. Alfalfa is the world's most important forage crop. It grows in association with S. meliloti, which is very important in terms of nitrogen fixation and, hence, global nitrogen cycling. This research project was aimed at understanding the effect of two ENPs (CeO2 and ZnO) on S. meliloti and alfalfa, separately, and on their symbiosis. This investigation was completed in three phases. Initially, the associated bacterium was treated, separately, with CeO2 and ZnO NPs. Ten nm CeO2 and ZnO NPs were exposed towards S. meliloti at 10, 31, 62.5,125, and 250 mg/l in liquid Yeast Mannitol Broth (YMB). Toxicological parameters evaluated included UV/Vis measurement of minimum inhibitory concentration, disk diffusion tests, and dynamic growth. Advanced scanning transmission electron microscope (STEM) and infrared spectroscopy (FTIR) were utilized to determine the spatial distribution of NPs and macromolecule changes in bacterial cells, respectively. Results indicate that ZnO NPs were more toxic than CeO2 NPs in terms of inhibition of dynamic growth and viable cells counts. STEM images revealed that CeO2 and ZnO NPs were found on bacterial cell surfaces and ZnO NPs were internalized into the periplasmic space of the cells. FTIR spectra showed changes in protein and polysaccharide structures of extra cellular polymeric substances present in bacterial cell walls treated with both NPs. The growth data showed a bacteriostatic effect of CeO2 NPs, whereas ZnO NPs was bactericidal to S. meliloti. Overall, ZnO NPs were found to be more toxic than CeO2 NPs to S. meliloti. In phase II, the alfalfa plant in association with S. meliloti, were cultivated for 30 d in soil treated with ZnO NPs, ionic (ZnCl2) and bulk ZnO, concentrations ranging from 0 (control)-750 mg kg-1. Plant growth, Zn bioaccumulation, dry biomass, leaf area, total protein, and catalase (CAT) activity were measured. Results showed 50% germination reduction by bulk ZnO at 500 and 750 mg/kg and all ZnCl2 concentrations. ZnO NPs and ionic Zn reduced root and shoot biomass by 80% and 25%, respectively. Conversely, bulk ZnO at 750 mg/kg increased shoot and root biomass by 225% and 10%, respectively, compared to control. At 500 and 750 mg/kg, ZnCl2 reduced CAT activity in stems and leaves. Total leaf protein significantly decreased as external ZnCl2 concentrations increased. STEM analysis revealed the presence of ZnO particles in tissues, suggesting the uptake of NPs. However, ZnO NPs showed less toxicity compared to ZnCl2 on measured traits. Phase III was performed in soil treated with either ZnO or CeO2 NPs at 0, 250, 500, and 750mg/kg for 30 days to study the toxicity effect of ZnO and CeO2 towards alfalfa's secondary metabolites and antioxidative properties. The toxicity was evaluated for leaf using chlorophyll (a & b), carotenoids, phenolic, and flavonoid contents. Results showed that, compared to control, leaf chlorophyll a content reduced to 60% and 40% at 750 mg/kg of CeO2 and ZnO NP treatments, respectively. Chlorophyll b reduced by 64%, 48%, and 60% at 250, 500 and 750 mg/kg CeO2 NP treatments, while chlorophyll b remained the same except 40% reduction at 750 mg/kg bulk ZnO treatment. CeO2 NPs enhanced the root flavonoids content by 34% at 750 mg/kg treatment and 86% in shoot at 500 mg/kg treatment, compared to control. Total root flavonoids decreased by 49% in plants treated with 750 mg/kg of ZnO NP treatment, whereas total flavonoids in shoots remained similar to control in all treatments, except 250 mg/kg ZnO NP treatment, where the flavonoid content decreased to 77%. This is the first complete study in a symbiotic system in terms of nano, bulk and ionic Zn species comparison in soil matrix. In addition, to the best of the authors' knowledge, this is the first report on the effects ZnO and CeO2 on alfalfa's secondary metabolites and chlorophyll content. Our results will help to reveal the toxicity of CeO2 and ZnO NPs on alfalfa and S. meliloti species, as well as to understand the eco-toxicity of NPs in plant-microbe symbiosis.
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Claims 20
Claim · model-written summary
ZnO nanoparticles inhibited S. meliloti growth and viable counts more than CeO2 nanoparticles.
- Taxon
- alfalfa
Medicago sativae1 - Treatment
- ZnO NPse0
- Interactor
- Sinorhizobium meliloti
Sinorhizobium melilotie1symbiont - Outcome
- inhibition of dynamic growth and viable cells countse0
- Direction
- more toxice0
- Comparator
- CeO2 NPse0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Results indicate that ZnO NPs were more toxic than CeO2 NPs in terms of inhibition of dynamic growth and viable cells counts.”
e1“alfalfa (Medicago sativa L.)-Sinorhizobium meliloti”
Claim · model-written summary
CeO2 and ZnO nanoparticles occurred on bacterial cell surfaces, with ZnO also internalized into periplasm.
- Taxon
- alfalfaMedicago sativae1
- Interactor
- Sinorhizobium melilotiSinorhizobium melilotie1symbiont
- Outcome
- ZnO NPs were internalized into the periplasmic space of the cellse0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“STEM images revealed that CeO2 and ZnO NPs were found on bacterial cell surfaces and ZnO NPs were internalized into the periplasmic space of the cells.”
e1“alfalfa (Medicago sativa L.)-Sinorhizobium meliloti”
Claim · model-written summary
Both nanoparticle treatments changed bacterial extracellular protein and polysaccharide structures.
- Taxon
- alfalfaMedicago sativae1
- Treatment
- both NPse0
- Interactor
- Sinorhizobium melilotiSinorhizobium melilotie1symbiont
- Outcome
- protein and polysaccharide structurese0
- Direction
- changese0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“FTIR spectra showed changes in protein and polysaccharide structures of extra cellular polymeric substances present in bacterial cell walls treated with both NPs.”
e1“alfalfa (Medicago sativa L.)-Sinorhizobium meliloti”
Claim · model-written summary
CeO2 nanoparticles were bacteriostatic to S. meliloti.
- Taxon
- AlfalfaMedicago sativat0
- Treatment
- CeO2 NPse0
- Interactor
- S. melilotiSinorhizobium melilotie0symbiont
- Outcome
- bacteriostatic effecte0
Not reportedComparatorDirection
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“The growth data showed a bacteriostatic effect of CeO2 NPs, whereas ZnO NPs was bactericidal to S. meliloti.”
t0“Alfalfa (Medicago Sativa)”
Claim · model-written summary
ZnO nanoparticles were bactericidal to S. meliloti.
- Taxon
- AlfalfaMedicago sativat0
- Treatment
- ZnO NPse0
- Interactor
- S. melilotiSinorhizobium melilotie0symbiont
- Outcome
- bactericidal to S. melilotie0
Not reportedComparatorDirection
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“The growth data showed a bacteriostatic effect of CeO2 NPs, whereas ZnO NPs was bactericidal to S. meliloti.”
t0“Alfalfa (Medicago Sativa)”
Claim · model-written summary
Bulk ZnO at 500 and 750 mg/kg reduced alfalfa germination by 50%.
- Taxon
- alfalfaMedicago sativae1
- Treatment
- bulk ZnO at 500 and 750 mg/kge0
- Interactor
- S. melilotiSinorhizobium melilotie1symbiont
- Outcome
- germinatione0
- Direction
- reductione0
- Value
- 50%e0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Results showed 50% germination reduction by bulk ZnO at 500 and 750 mg/kg and all ZnCl2 concentrations.”
e1“alfalfa plant in association with S. meliloti”
Claim · model-written summary
ZnCl2 at all tested concentrations reduced alfalfa germination by 50%.
- Taxon
- alfalfaMedicago sativae1
- Treatment
- all ZnCl2 concentrationse0
- Interactor
- S. melilotiSinorhizobium melilotie1symbiont
- Outcome
- germinatione0
- Direction
- reductione0
- Value
- 50%e0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Results showed 50% germination reduction by bulk ZnO at 500 and 750 mg/kg and all ZnCl2 concentrations.”
e1“alfalfa plant in association with S. meliloti”
Claim · model-written summary
ZnO NPs reduced root and shoot biomass by 80%.
- Taxon
- AlfalfaMedicago sativat0
- Treatment
- ZnO NPse0
- Outcome
- root and shoot biomasse0
- Direction
- reducede0
- Value
- 80%e0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“ZnO NPs and ionic Zn reduced root and shoot biomass by 80% and 25%, respectively.”
t0“Alfalfa (Medicago Sativa)”
Claim · model-written summary
ionic Zn reduced root and shoot biomass by 25%.
- Taxon
- AlfalfaMedicago sativat0
- Treatment
- ionic Zne0
- Outcome
- root and shoot biomasse0
- Direction
- reducede0
- Value
- 25%e0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“ZnO NPs and ionic Zn reduced root and shoot biomass by 80% and 25%, respectively.”
t0“Alfalfa (Medicago Sativa)”
Claim · model-written summary
Bulk ZnO at 750 mg/kg increased shoot biomass by 225%.
- Taxon
- AlfalfaMedicago sativat0
- Treatment
- bulk ZnO at 750 mg/kge0
- Outcome
- shoote0
- Direction
- increasede0
- Value
- 225%e0
- Comparator
- controle0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“bulk ZnO at 750 mg/kg increased shoot and root biomass by 225% and 10%, respectively, compared to control.”
t0“Alfalfa (Medicago Sativa)”
Claim · model-written summary
Bulk ZnO at 750 mg/kg increased root biomass biomass by 10%.
- Taxon
- AlfalfaMedicago sativat0
- Treatment
- bulk ZnO at 750 mg/kge0
- Outcome
- root biomasse0
- Direction
- increasede0
- Value
- 10%e0
- Comparator
- controle0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“bulk ZnO at 750 mg/kg increased shoot and root biomass by 225% and 10%, respectively, compared to control.”
t0“Alfalfa (Medicago Sativa)”
Claim · model-written summary
ZnCl2 at 500 and 750 mg/kg reduced CAT activity in stems and leaves.
- Taxon
- AlfalfaMedicago sativat0
- Organ / stage
- stems and leavese0
- Treatment
- ZnCl2e0
- Outcome
- CAT activitye0
- Direction
- reducede0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“At 500 and 750 mg/kg, ZnCl2 reduced CAT activity in stems and leaves.”
t0“Alfalfa (Medicago Sativa)”
Claim · model-written summary
Total leaf protein decreased significantly with increasing external ZnCl2 concentration.
- Taxon
- AlfalfaMedicago sativat0
- Treatment
- external ZnCl2 concentrationse0
- Outcome
- Total leaf proteine0
- Direction
- decreasede0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Total leaf protein significantly decreased as external ZnCl2 concentrations increased.”
t0“Alfalfa (Medicago Sativa)”
Claim · model-written summary
ZnO particles were observed in plant tissues, suggesting uptake.
- Taxon
- AlfalfaMedicago sativat0
- Outcome
- presence of ZnO particles in tissuese0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“STEM analysis revealed the presence of ZnO particles in tissues, suggesting the uptake of NPs.”
t0“Alfalfa (Medicago Sativa)”
Claim · model-written summary
ZnO nanoparticles showed less toxicity than ZnCl2 on measured traits.
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“ZnO NPs showed less toxicity compared to ZnCl2 on measured traits.”
t0“Alfalfa (Medicago Sativa)”
Claim · model-written summary
At 750 mg/kg, CeO2 nanoparticles reduced leaf chlorophyll a content to 60% of control.
- Taxon
- AlfalfaMedicago sativat0
- Treatment
- CeO2e0
- Outcome
- leaf chlorophyll a contente0
- Direction
- reducede0
- Value
- 60%e0
- Comparator
- controle0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“compared to control, leaf chlorophyll a content reduced to 60% and 40% at 750 mg/kg of CeO2 and ZnO NP treatments, respectively.”
t0“Alfalfa (Medicago Sativa)”
Claim · model-written summary
At 750 mg/kg, ZnO NP treatments nanoparticles reduced leaf chlorophyll a content to 40% of control.
- Taxon
- AlfalfaMedicago sativat0
- Treatment
- ZnO NP treatmentse0
- Outcome
- leaf chlorophyll a contente0
- Direction
- reducede0
- Value
- 40%e0
- Comparator
- controle0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“compared to control, leaf chlorophyll a content reduced to 60% and 40% at 750 mg/kg of CeO2 and ZnO NP treatments, respectively.”
t0“Alfalfa (Medicago Sativa)”
Claim · model-written summary
CeO2 nanoparticles reduced chlorophyll b by 64%, 48%, and 60% at 250, 500, and 750 mg/kg.
- Taxon
- AlfalfaMedicago sativat0
- Treatment
- CeO2 NP treatmentse0
- Outcome
- Chlorophyll be0
- Direction
- reducede0
- Value
- 64%, 48%, and 60%e0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Chlorophyll b reduced by 64%, 48%, and 60% at 250, 500 and 750 mg/kg CeO2 NP treatments”
t0“Alfalfa (Medicago Sativa)”
Claim · model-written summary
CeO2 nanoparticles increased root and shoot flavonoids at the reported doses.
- Taxon
- AlfalfaMedicago sativat0
- Treatment
- CeO2 NPse0
- Outcome
- root flavonoids contente0
- Direction
- enhancede0
- Value
- 34%e0
- Comparator
- controle0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“CeO2 NPs enhanced the root flavonoids content by 34% at 750 mg/kg treatment and 86% in shoot at 500 mg/kg treatment, compared to control.”
t0“Alfalfa (Medicago Sativa)”
Claim · model-written summary
ZnO nanoparticles at 750 mg/kg reduced total root flavonoids by 49%.
- Taxon
- AlfalfaMedicago sativat0
- Treatment
- 750 mg/kg of ZnO NP treatmente0
- Outcome
- Total root flavonoidse0
- Direction
- decreasede0
- Value
- 49%e0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Total root flavonoids decreased by 49% in plants treated with 750 mg/kg of ZnO NP treatment”
t0“Alfalfa (Medicago Sativa)”
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Claims are grouped by organism, treatment and what was measured or targeted. A paper counts as positive when any of its claims in the group is positive.