بررسی همدمای جذب آهن در توده زنده و مرده باسیلوس سوبتیلیس و سودوموناس پوتیدا

Background and Objectives
Increasing effluents production and discharging them as untreated into aqueous and terrestrial ecosystems, leads to contamination and imbalance of the ecosystems. Contaminants may include heavy metals or even nutritional elements. Small amounts of heavy metals such as iron (Fe) around living things are needed for their life, but high amounts of these metals are toxic and the accumulation of these metals in habitats is fatal for them. Bioremediation has been suggested as a clean technology, in which microorganisms are used in order to remove contaminants. Bacteria are efficient structures for metal ion detoxification due to their abundance, small size and large specific surface area. Also, they have high stability to survive in polluted habitats. In this research, the ability of two species of bacteria, Bacillus subtilis and Pseudomonas putida, which had a high capacity for the accumulation of metal ions, were compared in absorbing iron from aqueous solution in two living and non-living states, keeping the absorption efficiency characteristics constant. It is obvious that both alive or dead masses of these bacteria, which have a high function in absorbing and storing iron, can be used to make bio-purifiers or bio-fertilizers.
Methodology
In this study, the effects of two bacterial species as alive or dead biomass were investigated on the biosorption of iron. Biomasses were prepared and purified from two species of bacteria, Pseudomonas putida and Bacillus subtilis. Their dead mass was made by sterilization. Moreover, a constant volume of 1.5 ml of the biomass of bacteria grown in broth media was isolated in the bottom of 2 ml vials. Then sorption isotherm experiments of Fe from iron solutions with different concentrations (0, 5, 10, 20, 50, 75, 100, 120, 150 and 200) mgL-1 in 0.01‌ M sodium nitrate solution and fixed pH values of 2.5 were investigated. In this research, by keeping constant the parameters affecting absorption such as initial pH and fixed volume of solution, amount of biomass, equilibrium time and temperature, the ability and speed of absorption by bacteria was tested only by increasing the concentration of Fe. Then, by measuring the difference in the amount of ions remaining in the solution from the initial amount used, the amount of absorbed ions was obtained. Linear, Langmuir, Freundlich and Temkin isotherm models were used to analyze the adsorption data. This was a factorial experimental research with a completely randomized basic design that was done in three replications. The average absorption of Fe was tested by Duncan's method and SAS 9.4 software.
Findings
The isotherm of iron absorption in bacteria showed that the maximum amounts of iron absorption in Bacillus subtilis in live and dead forms were 41.9 and 49.2 mg/g and in live and dead Pseudomonas putida were 24.6 and 25.1 mg/g, respectively. This shows the ability of Bacillus subtilis for absorption of iron from aqueous solution was higher than Pseudomonas putida by increasing Fe concentrations in constant pH, biomass quantity and temperature. On the other hand, the absorption of iron in the dead mass of bacteria compared to their live mass was higher. The isothermal investigations in elimination of iron metal from aqueous solution showed that among the tested models, the Linear, Freundlich and Temkin models were suitable. This study was done in 3 replicates, so the effect of experimental factors (bacteria species and viability) on the coefficients of the Linear, Freundlich and Temkin equations were also statistically tested. Among the experimental factors, only the bacterial species had significant effects on a and b coefficients of the Linear model and the Bt coefficient of the Temkin model, so the mean tests were only done for these parameters.
Conclusion
Examining absorption diagrams and also testing coefficients a and b of Linear equations and Bt of Temkin showed that Bacillus subtilis has more affinity and better retention capacity to absorb iron from aqueous solutions. Examining the Temkin model coefficient showed that the heat released after the absorption process in this bacterium is less than Pseudomonas putida. However, Bacillus subtilis had higher capacity and affinity for absorption of iron than Pseudomonas putida, so it was a more suitable adsorbent in all Fe concentrations. The ability of the living and non-living masses of Bacillus subtilis to absorb iron makes it a good candidate for research in the fields of biomining of heavy metals, bioremediation of contaminated waters and/or making biofertilizers.