مجله زیست شناسی خاک
سال دهم شماره 2 (پاییز و زمستان 1401)

The increasing accumulation of plastic waste is one of the main environmental challenges currently facing human societies. Environmental toxicity of nano∕microplastics as newly known pollutants is a constant threat to terrestrial, marine, and atmospheric ecosystems. Nanoplastics are well able to pass through cell membranes and enter the cell, disrupting all vital functions of living organisms, including humans, plants, and microorganisms. Nano∕microplastics are considered a serious global pollutant due to their resistance to decomposition. Therefore, increasing efforts have been made to eliminate or reduce nano∕microplastics through eco-friendly technologies. Bio-enzymes have been evaluated as efficient agents for plastic degradation. A variety of plastic-degrading enzymes have been discovered among microbial communities. However, naturally occurring plastic degrading enzymes are not suitable for synthetic plastic degradation due to poor thermos-stability and low catalytic activity. Therefore, exploration in various environments to discover new plastic-degrading enzymes with desirable properties and functions has been increasingly considered. In the biological approach, the decomposition of nano/microplastics, increasing the efficiency of depolymerization, and optimizing the activity and thermal stability of the enzymes involved, have been investigated in various ways. Recent research efforts have made significant progress in discovering and engineering plastic decomposing enzymes, showing great promise for the suitable treatment for plastics biodegradation.

Due to the inevitable entry of cadmium into the soils and its high toxicity, it is essential to prevent it from human food chains. Biofilm-forming plant growth-promoting bacteria with the ability of auxin production can prevent the transport of some heavy metals to plants. A hydroponic factorial experiment was designed based on a randomized complete block in three replications to investigate the effect of biofilm-forming plant growth-promoting bacterium and tryptophan on yield and cadmium uptake in Rye. Experimental factors include three levels of cadmium (zero, 50 and, 100 mg.L-1), two bacterial inoculation (with or without Bacillus atrophaeus) and, tryptophan (presence in 100 mgL-1 and absence). The results showed that the addition of tryptophan and bacterial inoculation could increase the yield of rye dry matter by 19% on average vs control. In addition, the co-applying of tryptophan with bacterial inoculation was able to reduce 100% and 62% of the cadmium concentration in rye aerial parts at 50 and 100 mg.L-1, respectively. The use of tryptophan by the improvement of the antioxidant system was able to reduce the amount of malondialdehyde and hydrogen peroxide at 50 mg.L-1 cadmium level up to 30 and 42%, and for 100 mg.L-1 cadmium by 34 and 32%, respectively. Therefore, it seems that with further studies, these treatments can be used to increase the yield and reduce the Cd entry into the food chain in the Cd-contaminated soils.

This study aimed to investigate the effect of Amoxicillin, Cefixime, and Metronidazole on some biological properties such as basal respiration, substrate-induced respiration, and bacterial abundance in uncontaminated and heavy metal-contaminated soils. The experiment has performed with a completely randomized factorial design with three replications. Factors include three soil types (heavy metal contaminated mine soil, rangeland soil near mine, and agricultural soil), seven antibiotic treatments (control, Amoxicillin, Cefixime, and Metronidazole, each one 100 and 200 mg per kg of dry soil) and three incubation times: short-time (zero-7 days), medium-time (15 and 30 days) and long-time (60 and 90 days)). The results showed that in the medium time, the application of 200 mg.kg-1 of antibiotics amoxicillin in agricultural soil and metronidazole in mine soil, resulted in the highest (8.4958) and lowest (4.4594) logarithm of the abundance of all soil bacteria. Rangeland soil had the highest basal respiration amount (0.1066 mg CO2. g-1dry soil. day-1) in short-time incubation, and agricultural soil had the lowest basal respiration amount in both long-time (0.0144) and medium-time (0.0172). The use of 100 mg of metronidazole per kg of rangeland soil in the short time resulted in the highest amount of substrate-induced respiration (0.0251 mg CO2. g-1 dry soil. h-1) and the use of 100 mg of amoxicillin per kg of agricultural soil in the medium incubation time resulted in the lowest substrate-induced respiration (0.0027). It seems that agricultural soil showed the highest abundance of bacteria and mine soil showed the highest amount of substrate-induced respiration. Rangeland soil had the highest amount of basal respiration and there was no significant difference with agricultural soil in the abundance of bacteria and mine soil in the amount of substrate induced respiration. Mine soil showed the lowest abundance of bacteria and agricultural soil showed the lowest amount of basal and substrate induced respiration. The application of metronidazole resulted in the highest amount of basal and substrate induced respiration, and the lowest abundance of bacteria. The application of amoxicillin and Cefixime showed the highest abundance of bacteria and the lowest amount of substrate induced respiration, respectively. Incubation in a short time had the highest amount of basal and substrate induced respiration. The highest abundance of bacteria and the lowest amount of substrate induced respiration were observed in the medium time. The long-time incubation showed the lowest abundance of bacteria and the lowest basal respiration amount.

One of the main reasons for the low yield of biofertilizers in fish ponds is the use of insoluble mineral phosphorus sources (often tri-calcium phosphate) during the process of isolation and evaluation of phosphorus-releasing microorganisms. A large part of insoluble phosphorus (50 to 90%) in warm water fish ponds is insoluble organic phosphorus. Therefore, it seems phosphorus-releasing microorganisms isolated solely from mineral phosphorus sources can not be effective as biofertilizers in warm water fish ponds. The aim of this study was to isolate phosphorus-releasing bacteria from warm water fish ponds using NBRIP medium containing organic phosphorus source (calcium phytate) and compare their performance with bacteria derived from insoluble mineral phosphorus source (tri-calcium phosphate) in microcosm conditions (Erlenmeyer contains sediment: conditions similar to a fish pond). The phosphorus release ability of isolates (33 organic isolates and 19 inorganic isolates) was evaluated in NBRIP solid and liquid medium. The range of soluble phosphorus in the liquid medium containing calcium phytate varied between 57.40 - 141.93 and 108.16 - 219.49 mg/l in the medium containing tricalcium phosphate. In the final step, evaluation of isolates in sediment microcosm showed that three isolates from organic phosphorus source (3P, 13P, and 2P) were the best phosphorus release isolates (with 11.86, 12.53, and 28.18 mg / l respectively) and had better performance compared to isolates from mineral phosphorus source. Molecular identification showed these isolates belonged to priestia aryabhattai, Bacillus zanthoxyli, and Acinetobacter johnsonii. Due to the pathogenic potential of A. johnsonii for fish and humans, the Bacillaceae family strains can be considered candidates for use in biofertilizers for further evaluation.

In this study, keratinase-producing bacteria were used to produce natural fertilizer from chicken feathers. Twenty-nine soil samples were collected from 0-30 cm depth of agricultural fields and mixed with chicken feathers. After three weeks, 31 isolates were isolated from the soils mixed with feathers, which were able to grow on the special culture medium of Feather Meal Agar (FMA). The isolates were transferred to a liquid medium containing feathers and their ability to degrade the feathers was investigated. A completely randomized design was used to examine the effect of the solution created by the degradation of chicken feathers on lettuce growth. The experimental treatments included the foliar application of three solutions obtained from the degradation of chicken feathers (gh1, b1, c11), and control (distilled water). The results showed eight isolates were able to completely decompose the feathers in seven days by producing keratinase enzyme. The highest activity of the keratinase enzyme (with the ability to fully degrade the feather: 8.56 U / ml) was related to that of Bacillus methylotrophic strain gh1. Also, the maximum concentration of free amino acid (1065 μg / ml) was observed in the growth medium of Bacillus siamensis strain c11. The three solutions obtained from feather degradation had a significant effect (p < 0.01) on lettuce fresh weight, lettuce dry weight, and fresh root weight. The results showed that the lettuce fresh weight increased by 28.8%, 26.1%, and 14.1%, using Bacillus methylotrophicus (gh1), Bacillus velezensis (b1), and Bacillus siamensis (c11) respectively, compared to the control. In addition, the lettuce dry weight increased by 25.7%, 19.9%, and 15.2%, with the aid of gh1, b1, and c11 treatments, respectively, compared to the control. The results showed that using keratinase-producing bacteria, feather degradation could be increased, and the obtained product can be used as a growth stimulant for lettuce.