Soil science
S. Balandeh; A. Lakzian; A. Javadmanesh
Abstract
Introduction: Silver nanoparticles (AgNPs) have a broad spectrum of uses, therefore, AgNPs will be released from those products into many different ecosystems. In the last decades, AgNPs have received substantial attention due to their distinctive physical and chemical properties such as high thermal ...
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Introduction: Silver nanoparticles (AgNPs) have a broad spectrum of uses, therefore, AgNPs will be released from those products into many different ecosystems. In the last decades, AgNPs have received substantial attention due to their distinctive physical and chemical properties such as high thermal and electrical conductivity, chemical stability, catalytic activity and antimicrobial properties against microbes such as bacteria, fungi, and viruses. There are many parameters for assessment effect of toxicity due to AgNPs but soil microbial community is one of which considered being an important target for assessing the impact of manufactured nano-materials on the terrestrial environment. Toxicity of AgNPs is due to the physical interaction of AgNPs with microorganisms and the production of reactive oxygen species (ROS). Although as we have been known harmful effects of AgNPs on the soil bacterial community, but the most information about antimicrobial properties of AgNPs come from the routine lab instructions such as soil respiration, substrate induced respiration and microbial biomass and colony forming unite. So, the objective of this paper was to study the effects of silver nanoparticles on microbial activity using the routine lab instructions and compare with the obtained data from the molecular genetic techniques. In this paper, the quantitate population of soil bacterial was estimated using Real time qPCR with the MIQE guidelines. Materials and Methods: In order to study the effect of silver nanoparticles on microbial activity and bacterial population in a calcareous soil, an experiment was conducted as a completely randomized design based on factorial arrangement with three replications. Experimental factors included silver slat forms (AgNPs and AgNO3), Ag concentrations (0, 0.5, 5, 10, 50, and 100 mg Ag kg-1 dry soil) and incubation time (7 and 42 days). Soil samples (Typic Haplicambids) with clay loam texture and seven percent of calcium carbonate was collected from Research Field of Ferdowsi University of Mashhad, Mashhad, Khorasan Razavi, Iran. The soil samples were amended with different concentrations of AgNPs and incubated at 25oC for 42 days. The water content of soil samples was adjusted at 70% WHC during the incubation time. After 7 and 42 days of incubation, the soil substrate-induced respiration (SIR), heterotrophic plate count (HPC), and soil urease and dehydrogenase activities were measured. Finally, based on the obtained data, the soil biological quality index was estimated using the soil biological parameters. In order to quantify the total bacterial population, DNA was extracted from soil samples and was estimated using the relative concentration of 16S rDNA gene by a quantitative Polymerase Chain Reaction (qPCR), with a minimum information for publication of quantitative real-time PCR experiments (MIQE) guidelines. Results and Discussion: The results showed that with increasing the concentration of both AgNPs and AgNO3, the activity of dehydrogenase and urease in soil samples decreased during the incubation times. Microbial substrate induced respiration (SIR) and the total bacterial population in soil samples considerably declined at the end of experiment. Bacterial population in AgNPs treatments decreased compared to AgNO3 treatments but the reduction was not statistically significant. Over time, soil dehydrogenase activity and soil SIR decreased in both AgNPs and AgNO3 treatments, while soil urease activity and heterotrophic bacterial populations improved but again in heterotrophic bacterial populations was not statistically significant. The soil biological quality index was estimated from the soil biological data. AgNO3 treatments reduced the soil biological quality index compared to AgNPs treatments. In other words, the results showed that AgNO3 was more toxic to soil bacteria activity compared to AgNPs. The lowest soil urease and dehydrogenase enzyme activity and soil biological quality index were observed in the treatment of 100 mg kg-1 dry soil AgNO3 after 7 days of incubation. The application of 0.5, 5, 10, 50, and 100 mg Ag kg-1 dry soil decreased relative soil bacterial population by 22%, 40%, 59%, 73%, and 82% in AgNO3 treatment and 10%, 30%, 68%, 76%, and 86% in AgNO3 treatment compared to control after 42 days of incubation, respectively. Conclusion: The results of this study showed that silver nanoparticles can negatively affect the enzymes involved in the nitrogen and carbon cycle. The AgNPs had less toxicity effect on the soil microbial activity compared to AgNO3. However, AgNPs was more toxic to soil bacteria populations compared to AgNO3. Different behavior AgNPs and AgNO3 in calcareous soil needs more investigations but there is no doubt that AgNPs is as an emerging contaminant and it has high toxicity potential for soil microbial community.
S. Abdollahi; A. Golchin; F. Shahryari
Abstract
Introduction: Contamination of soils with heavy metals is one of the most serious environmental problems increasing the risk of the entry of heavy metals into food chains. Rhizosphere soil is distinct from the bulk soil and is defined as the volume of soil around living roots which is influenced by root ...
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Introduction: Contamination of soils with heavy metals is one of the most serious environmental problems increasing the risk of the entry of heavy metals into food chains. Rhizosphere soil is distinct from the bulk soil and is defined as the volume of soil around living roots which is influenced by root activities. Enzymes are produced by both roots and soil microorganisms to alter nutrient availability in rhizosphere soil. Soil enzymes promote the transformation of matter and energy in the soil, and their activity has a close relationship with soil nutrient availability. Detection of microbial enzymes in a natural environment is important to understand biochemical activities and to verify the biotechnological potential of microorganisms. However, there are few reports to indicate the biotechnological potential of plant growth promoting rhizobacteria (PGPR) and their effects on the activity of bacterial enzymes in rhizosphere soils under the stress of heavy metals. Thus, in the present study lead and cadmium contaminated rhizosphere soils were inoculated with PGPR species to investigate the influence of these bacteria on the activity of some enzymes. Materials and Methods: A factorial pot experiment with completely randomized design base and three replications was performed in the greenhouse conditions. The factors examined were (a) rhizosphere soils of three varieties of cabbage [Brassica oleracea var. acephala L. (Ornamental cabbage), Brassica oleracea var. italica L. (Broccoli cabbage) and Brassica oleracea var. capitata L. (Cabbage)] and (b) five species of PGPR, consisting Pseudomonas putida PTCC 1694, Bacillus megaterium PTCC 1656, Proteus vulgaris PTCC 1079, Bacillus subtilis PTCC 1715 and Azotobacter chroococcum, used to inoculate the rhizosphere soils. There was also a control treatment (without rhizobacteria). The experiment had 18 treatments and there were 54 experimental units. To study rhizosphere soils, several rhizoboxes were used and three seedlings of cabbage were planted in the central part of each rhizobox (rhizosphere area). In treatments inoculated with rhizobacterial species, 2 ml of a bacterial suspension with 107-108 (cfu ml-1) was used to inoculate the soil of rootzone. After three months, cabbage varieties were harvested and the activity of alkaline phosphatase, acid phosphatase, urease, and dihydrogenase were measured in rhizosphere soils. The data obtained from this study were statistically analyzed by SPSS statistical software package (Version 9.4) and the variance of the data was analyzed by one-way ANOVAs (Duncan’s test) range test at 1 and 5 percent probability levels. Results and Discussion: The analysis of variance of the data (ANOVA) showed that the cabbage varieties, inoculation with PGPR species and their interactions had significant effects (p < 0.01) on the activity of alkaline phosphatase, acid phosphatase, urease, and dihydrogenase in rhizosphere soils. The results showed that inoculation of the rhizosphere soils with PGPR species increased the activity of soil enzymes. The highest activity of alkaline phosphatase (1529.28 µg pNP.g-1 dm.h-1) was measured in rhizosphere soils of the broccoli inoculated with Pseudomonas putida PTCC 1694. But, the highest activity of acid phosphatase (497.92 µg pNP.g-1dm.h-1) was obtained in rhizosphere soils of cabbage inoculated with Pseudomonas putida PTCC 1694. Also, the highest activity of urease (208.36 µg N-NH4+.g-1dm.2h-1) was observed in rhizosphere soils of the cabbage inoculated with Azotobacter chroococcum and the highest activity of dihydrogenase (8.71 µg TPF.g-1dm.16h-1) was observed when rhizosphere soils of the cabbage were inoculated with Bacillus subtilis PTCC1715. Conclusion: From the results of this study, it may be concluded that inoculation of Pb and Cd contaminated soils with PGPR species could modulate the toxic effects of heavy metals on plant and increase the activity of some key enzymes for plant growth in rhizosphere soils.
Samira Abduolrahimi; Nasrin Ghorbanzadeh; Akbar Forghani; Mohammad Bagher Farhangi
Abstract
Introduction: Cadmium is considered to be one of the heavy metals with the highest toxicity, because it has high activity and a relative high dissolution rate in water and in living tissues. In recent years, due to the high volume of natural resources pollution and the inefficiency of conventional physicochemical ...
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Introduction: Cadmium is considered to be one of the heavy metals with the highest toxicity, because it has high activity and a relative high dissolution rate in water and in living tissues. In recent years, due to the high volume of natural resources pollution and the inefficiency of conventional physicochemical methods for refining these resources and the occurrence of environmental crisis, bioremediation process has been at the forefront. Microbially induced calcite precipitation (MICCP) has been considered as a novel solution for these problems, and several bacterial species have been already utilized for MICCP. MICCP based degradation of urea occurs through the ureolytic pathway. Urease (urea amidohydrolase) is an enzyme that hydrolyzes urea into one mole of carbonate and two moles of ammonia per mole of urea. In this aspect, microbial mineral precipitation products such as calcite can strongly adsorb heavy metals on their surfaces and incorporate heavy metal ions into their crystal structure. Some studies have reported MICCP-based sequestration of soluble Cd via coprecipitation with calcite was useful for Cd bioremediation. Several bacterial species have been utilized for MICCP. The endospore forming bacteria Sporosarcina pasteurii have been shown to produce high levels of urease and have therefore been extensively studied. Sporosarcina pasteurii has attracted significant attention for its unique feature of calcium carbonate precipitation, which can be easily controlled. So, In the present study the ability of Sporosarcina pasteurii bacterium has been investigated in the remediation of Cd(II) in Cd-contaminated sandy soil based on MICCP method.
Materials and Methods: Sporosarcina pasteurii (PTCC 1645) was procured from Microbial Bank of Iran (Central Collection of Industrial Fungi and Bacteria, Karaj, Iran). The bacterial strain was inoculated into NB (nutrient broth) media containing 2% urea and 25 mM CaCl2 (NBU media) and then incubated at 37◦C for 6 days. The urease activity was determined at regular time intervals by measuring the amount of ammonia released from urea according to the phenol-hypochlorite assay. Minimum inhibitory concentration (MIC) test was performed to determine the lowest concentration of cadmium chloride, which prevents the growth of bacteria. Sporosarcina pasteuriiwas inoculated into NBU media supplemented with 0.5, 1,2,4,8 and 10 mmol l-1 Cd and incubated at 37◦C, 130 rpm for 50 hours. Control flasks without adding Cd were also incubated. Bacterial growth was determined in terms of optical density (OD) by measuring absorbance at a wavelength of 600 nm at regular time intervals (0, 10, 20, 30, 40 and 50 hours) and colony-forming units (CFU) were also counted. The cadmium removal in 0.5, 1 and 2 mM cadmium solutions (based on MIC) was measured.A sandy soil from a depth of 0 to 30 cm was sampled. The soil was polluted with 10, 20, 40 and 50 mg/kg of cadmium and incubated in room temperature for two weeks. After incubation time, the cadmium remediation studies were performed at 30◦C in the beakers containing 100 g of sterilized dried contaminated soils and 200 mL of overnight grown of Sporosarcina pasteurii (~ to 107cfu ml−1) in NBU media. For each treatment corresponding control were included with the same condition but without bacteria.After 7 days of incubation, urease and dehydrogenase enzymes activity and concentration of cadmium in soluble + exchangeable and carbonate fractions were measured. The concentration of cadmium in iron-manganese oxides, organic matter and residual fractions in concentration of 50 mg/kg cadmium was also determined according to the continual extraction procedure of Tessier et al. (1979).
Results and Discussion: The amount of released ammonia by ureolytic activity of Sporosarcina pasteurii increased up to fourth day and then became almost constant.Optical density in different concentrations of cadmium decreased in comparison to control treatment after 48 hours. The minimum inhibitory concentration of cadmium for bacteria growth was 2 mM as determined by colony counting after 48 hours of incubation. Cadmium removal efficacy from solutions containing 0.5, 1 and 2 mM of cadmium was 99.6, 99.8 and 99.8%, respectively. The amounts of urease and dehydrogenase activities in the presence of bacterium were significantly higher than control treatments (P≤0.05). The results of the fractionation of contaminated soils in the absence of Sporosarcina pasteurii showed the distribution of cadmium as organic matter
F. Aghababaei; F. Raiesi; alireza hosseinpuor
Abstract
Soil biota such as earthworms and arbuscular mycorrhizal fungi (AMF) play an important role in the stability of ecosystem, and the bioavailability of soil elements, in particular heavy metals, in soils. To examine the effects of these organisms, a 3×2×3 factorial experiment arranged as randomized complete ...
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Soil biota such as earthworms and arbuscular mycorrhizal fungi (AMF) play an important role in the stability of ecosystem, and the bioavailability of soil elements, in particular heavy metals, in soils. To examine the effects of these organisms, a 3×2×3 factorial experiment arranged as randomized complete design was set up to study the individual and combined influence of earthworms (Lumbricus rubellus L.) and AMF (Glomus mosseae and Glomus intraradices) on soil organic matter (OM), dissolve organic carbon (DOC), soil respiration, microbial biomass carbon (MBC), soil enzyme activity and glomalin production in a calcareous soil contaminated with 0, 10, 20 mg of Cd kg-1 soil cropped with sunflower (Helianthus annuus L.) with three replications. Both earthworms and mycorrhizal fungi were able to survive in all the treatments with added Cd. Results showed that Cd pollution decreased all the measured microbial activities and properties in soil. Earthworm treatment increased DOC by 4-10% at all Cd levels. The amount of soil MBC in mycorrhizal treatments was greater (1.9-2.4 times) than that in non-mycorrhizal treatment, and AMF inoculation increased MBC/TOC ratio from 23% to 53% in Cd-polluted soils. Earthworm and AMF enhanced soil enzyme activity/MBC ratio, 10-18 and 40-54% for soil alkaline phosphatase and 4-9 and 40-55% for soil urease, respectively. The glomalin production increased at 20 mg kg-1 and was about 15% greater in G. mosseae than in G. intraradices species. Although soil respiration was decreased substantially with Cd pollution, inoculation of either earthworms or AMF enhanced soil respiration when compared with the corresponding controls.
