Journal of Soil Biology
Year:2017 | Volume:5 | Issue:1 |Papers Count:7

Laccase is among the most important enzymes that has attracted much attention in the field of bioremediation in recent years, due to its ability to oxidize various compounds and persistent environmental pollutants. Since free from of Laccase has low operational stability with high cost of production, there are some limitations on the commercial applications in industrial and environmental biotechnology. In this regard, immobilization of such enzymes on absorbent surfaces can be a good way to increase stability and operational life of the enzyme. In order to examine the interactions between Laccase (Trametes versicolor) with Montmorillonite and zeolite minerals, three different experiments were done separately in a completely randomized design with two replications in vitro conditions. Experiments were included four levels of pH (5, 6, 7 and 8), nine levels of temperature (4oC and 10-80oC) and seven levels of incubation time (0, 1, 2, 5, 10, 20 and 30 days), respectively. Based on the results, the highest enzyme adsorption on the surface of studied minerals was observed in pH=5 and enzyme absorption decreased with increasing pH.Furthermore, the highest relative activities were obtained for free Laccase at 20oC, for immobilized Laccase on Montmorillonite at 80 and 4oC and for immobilized Laccase on zeolite at 4 and 70oC. Immobilized Laccase showed a remarkable stability to low and high temperatures. Maximum relative activity (100%) for immobilized Laccase on Montmorillonite and zeolite was observed in 20th day of incubation time and for free Laccase in 5th day of incubation time.Indeed, immobilization indicated a proper effect on Laccase enzyme activity retention.

Symbiotic bacteria associated with the root of legume plants were isolated from soil and the root nodules of alfalfa (Medicago sativa L.), chickpea (Cicer arietinumL.) and yellows alfalfa (Melilotus officinalis L.) grown in arseniccontaminated areas in south eastern part of Kurdistan province, Iran. According to physiological and biochemical properties, isolates were identified as the members ofRhizobium and Ensifer genus. The presence of arsenic resistant system known asars system was confirmed by amplification using primers corresponding toarsC gene. Growth rate of strains in different concentrations of arsenate was investigated in YEMB medium supplemented with 100-400 mM arsenate. Alfalfa, s isolates (AB1, AB3), chickpea, s isolates (PA2, PC2), yellow alfalfa, s isolate (YA1) and standard strain (Sinorhizobium meliloti SM117) were tolerant to 350 mM arsenate and (AB1, PA2 and YA1) isolates were moderately capable to grow at 400 mM arsenate. Among the identified strains, AB1 and PA2, were selected for greenhouse experiments. In order to evaluate the effect of arsenic contamination on legume-rhizobia symbiosis and biomass production of alfalfa and chickpea plants, an experiment was carried out based on a completely randomized design with a factorial arrangement in three replications. Experiment factors consisted of, three levels of rhizobia inoculation (with and without inoculation of AB1 and PA2) and five levels of arsenic concentrations (0.10, 50, 75 and 100 mgkg-1 soil) under greenhouse conditions for 8 weeks. Results obtained in this study indicated that the fresh weight and dry weight of alfalfa and chickpea (shoot and root) were decreased as the arsenic concentration of the soil was increased. The results also showed that fresh and dry shoot and root weight of alfalfa and chickpea were significantly higher in rhizobia-inoculated treatments compared to noninoculated plants.

Vermicompost technology is one of the most important tools for processing and converting organic wastes into biological fertilizers. The study intended to determine the best substrate for breeding earthworm speciesEisenia foetida in a completely randomized design with 10 treatments and four replications in a three-month period. Various substrates along with the remains of organic wheat straw and alfalfa in different ratios (25, 50, 75 and 100) were investigated in Year 2013 at the University of Gonbad-e Kavous. In this study, some characteristics of worms such as weight of adult worms, young, newborn, cocoon weight and final weight of earthworms, E. foetida, and growth rate, specific growth rate of the number of babies per generation and survival rates were studied.The results of analysis of variance showed that there were statisticallysignificant differences among all studied treatments from gain weight of adult worms, young, newborn and growth indices point of view except insurvival rates. The most weight gained with adult worms was found in the 1: 1 ratio of sheep manure along with alfalfa residues. However the greatest weight in young worms were obtained from sheep manure with straw treated in the ratio of 1: 3. The maximum weight of the baby worm and final weight were obtained from the worms in the straw mixed with sheep manure in the ratio of 1: 1. The results also showed that treatment of sheep manure with straw and alfalfa wastes had the greatest increase in worm weight.

Exopolysaccharides secreted by bacteria has an important role in bacterial resistance against stresses such as salinity. This study aimed to isolate and identify halotolerant bacteria with the most exopolysaccharide production potential of the soil and evaluate the production of exopolysaccharides in different salt concentrations. Soil samples were spread on nutrient agar ± %5 NaCl then among the salt tolerant colonies, the most tolerable salt concentration (MTC) of mucoid ones was isolated and the EPS production in the presence of (5%) salt concentrations was assayed. The nature of exopolysaccharide produced by superior strain was identified with FTIR Spectrometer and the exopolysaccharides production in higher concentrations of salt were determined by anthrone-sulfuric acid method. In the infrared spectrum of exopolysaccharide, the absorption peaks were attributed to the presence of carbohydrate compounds such as b-glucans and also to alcohol groups, phenols, carboxylic acids, carbonyl and alkyne. The exopolysaccharide production was significantly (Pvalue<0.05) increased by increasing salt stress. According to the results, the strain no-7 with growth potential on the 25% salt and producing exopolysaccharides (0.168 g /L) in 24 hours was selected as a superior strain and according to 16S rDNA gene sequencing was identified asCitrobacter freundiiATHM38 and submitted to GenBank under the accession number KX553903.

In order to study the growth and yield of wheat under dryland conditions, an experiment was carried out in factorial arrangement using randomized complete block design with three replications at Agricultural Research Station of Ilam University during 2013-2014 cropping season. Experimental factors consisted of two wheat cultivars (KerasSablan and Saji), chemical and biofertilizers.Treatments include 1- without application of phosphorous fertilizer, 2-full use of recommended phosphorous, 3- pseudomonas putida, 4- Fuuneliformis mosseae, 5- pseudomonas putida+Fuuneliformis mosseae, 6- pseudomonas putida+Fuuneliformis mosseae+1/2 use of recommended phosphorous, 7- pseudomonas putida+1/2 use of recommended phosphorous and 8- Fuuneliformis mosseae+1/2 use of recommended phosphorous. Results indicated that wheat cultivars and fertilizer treatments had significant effect on spike dry weight, stem dry weight, chlorophyll a and b contents, dry weight and root length, nitrogen, phosphorus, potassium, period of grain filling, grain filling rate, dry matter remobilization and current photosynthesis. Saji cultivar had the highest grain filling rate, dry matter remobilization and current photosynthesis. Biofertilizer treatments had positive effect on period of grain filling, grain filling rate, dry matter remobilization and current photosynthesis under dryland conditions.1/2 use of recommended phosphorous+Mycorrhiza fungi treatment had the highest period of grain filling, grain filling rate, dry matter remobilization, current photosynthesis, chlorophyll a and b contents, dry weight and root length, nitrogen, phosphorus and potassium. Therefore with regard to the fact that cultivation of wheat in dryland conditions is facing the terminal stresses such as drought and heat, the integration use of Saji cultivar along with fertilizer treatment ofFuuneliformis mosseae+1/2 use of recommended phosphorous due to high chlorophyll content, nutritious elements, rate and duration of grain filling and current photosynthesis can be effective for improving the wheat grain yield.

Heavy metals may increase antibiotic resistance in bacteria. The aim of this study was to determine antibiotic-resistance of frequent Gram-negative isolates in agricultural, pasture and mine soils. Hence, 97 isolates from soil samples were selected and antibiotic (7 antibiotics) and heavy metal resistance were determined by disc diffusion and MIC methods. Based on the results, 50% of the Azotobacters from agricultural soils and 28.57% of those from pastures showed multi-resistant against amoxicillin, ampicillin, vancomycine and tetracycline.62.5% of Enterobacter strains from agricultural soils, 33.33% of pastures isolates and 35% of the mining soils isolates showed resistance to these antibiotics.87.5% of the agricultural soilPseudomonas strains and 100% of pastures isolates showed also resistance to these antibiotics. According to the results, the resistance to streptomycin and doxycycline in three isolates was high, whereas it was the least for gentamicin. All isolates displayed resistance to lead and sensitivity to cadmium. All agricultural soil Azotobacter strains, 57% of pasture isolates and 66.7% of mining waste isolates were multi-resistant to Pb, Hg and Ni. Abundance of Enterobacters, resistant to these metals from agricultural, pasture and mining waste samples was 45.83, 80 and 65%.37.50 and 66.7% ofPseudomonas strains from agricultural and mining wastes showed also resistance to those metals. The high percentage of antibiotic-resistance may be attributed to the heavy metals in soils. Resistance to antibiotics in all soils was high. But, due to the favorable conditions of agricultural soils, it seems that dangerous antibiotic-resistant bacteria may be spreading much more faster.

Co-application of biological fertilizers and phosphate sources have greatly considered in calcareous soils in recent years. In order to study the effect of phosphate solubilizing bacterium (PSB), phosphate sources and vermicompost on some growth characteristics of lettuce (cv. Ferdos), a greenhouse experiment was conducted with factorial arrangement in a completely randomized design with three replications and three factors. Factors consisted of two levels of phosphate solubilizing bacterium (Pseudomonas flouresence) (with and without inoculation), two levels of vermicompost (0 and 1% w/w) and four phosphate sources (control, rock phosphate, tricalcium phosphate (TCP) and triple super phosphate at 25 mg P kg-1 soil). Biological fertilizers significantly increased shoot fresh and dry weights (SFDW), but they didn’t have remarkable effect on lettuce height. Application of rock phosphate and tricalcium phosphate (TCP) increased dry and fresh weight, respectively. Application of triple super phosphate significantly increased SFDW and lettuce height. Co-application treatments of bacterium, vermicompost and phosphate sources (except super phosphate) significantly increased SFDW, leave numbers and phosphorus concentration of lettuce. Overall, the results indicated that phosphorus chemical fertilizers can be replaced by co-application of insoluble phosphate and biological fertilizers.