The role of Ochrobactrum anthropi and Ochrobactrum tritici bacteria in biosorption of copper

hajar Abyar ¹ ( Department of Environmental Sciences, Faculty of Fisheries and Environmental Sciences, Gorgan University of Agricultural Sciences and Natural Resources, Gorgan 49189-43464, Iran. )
mohsen Nowrouzi ² ( Department of Science and Biotechnology, Faculty of Nano and Bio Science and Technology, Persian Gulf University, Bushehr 75169-13798, Iran )

Submited date : 2022-09-11 Accepted date : 2023-01-22

Keywords: Sediment, Biological removal, Khor Musa, Ochrobactrum sp,

Abstract :

The increasing development of industries and refineries has enhanced heavy metals as a worldwide environmental problem, which shows a potential threat to humans, animals, and plants due to their non-degradable and stable characteristics. Many heavy metal compounds are highly soluble in water which facilitates their easy transfer into the food chain and accumulation in the environment such as excessive amounts of heavy metals in sediments, wastes, and aquatic organisms. There is numerous microbial biomass with different enzymatic capabilities to bioremediate heavy metals such as fungi, bacteria, and algae. Bacteria with a high surface area to volume ratio and easy availability could adsorb heavy metals using functional groups such as hydroxyl, carbonyl, and carboxyl on their cell wall. Therefore, in this study, the use of biological and cost-effective methods to remove heavy metals from aqueous solutions was considered. For this purpose, the potential of marine bacteria isolated from Khor Musa sediments, which are located in the northwest Persian Gulf, in removing copper was evaluated. The sediment samples were diluted in the NaCl solution and cultivated on the nutrient agar media containing copper concentrations of 10, 50, and 100 mg/L. After 3 days of incubation at 30 °C, the bacteria colonies on the media with a 100 mg/L copper concentration were isolated and purified for further assessment. The primary identification of the isolated bacteria was performed using gram staining and the potassium hydroxide (KoH) test. Then, biochemical tests and the 16S rRNA sequence were utilized to accomplish the bacterial identification. The potential of isolated bacteria in copper removal was evaluated under 50, 100, and 200 mg/L copper concentrations for 150 min. The sampling was performed in 30 min intervals using atomic absorption spectroscopy. Cultivation of sediment samples in a nutrient agar medium containing concentrations of 10 to 100 mg/L of copper led to the isolation and identification of two resistant bacteria from the genus Ochrobactrum sp. Both bacteria were gram-negative and rod-shaped, positive mobility and oxidase tests, negative methyl red (MR) and Voges-Proskauer (VP), and H2S producing in triple sugar iron agar (TSI) test. Furthermore, glucose and maltose tests indicated that the isolated bacteria were oxidative. The bacterium O. anthropi strain YX0703 illustrated a remarkable performance in which that removed 71.08% and 63.96% of copper metal in concentrations of 100 and 200 mg/L, respectively. In addition, a range of copper removal in a concentration of 50 mg/L was from 47.3% after inoculation, to 72.6% at 120 min. The maximum removal of copper was observed in the first 60 min of exposure to the metal equivalent to 64.92%. While, the highest percentage of metal removal by O. tritici strain AN4 was obtained at a concentration of 50 mg/L, equivalent to 72.62%, and when the concentration increased to 200 mg/L, the removal rate decreased to 49.97%. It is noteworthy to mention that O. tritici strain AN4 removed 58.22% of copper at a concentration of 100 mg/L in 90 min while the removal trend was relatively constant after 90 min exposure to the copper. The samples containing copper without bacterial inoculation were considered as control which showed a constant concentration during the experiments. Comparing the amount of copper absorbed by bacteria in different concentrations showed a significant difference (p<0.05) and with the increase in copper concentration, the amount of metal absorbed by bacteria enhanced. In fact, the biosorption of metal ions to the cell wall of microorganisms continues until a balance is established between the absorbed ions and the number of remaining ions in the solution, therefore, at high concentrations due to the abundance of metal ions, more ions must be absorbed by the bacteria. According to the obtained results, more than 70% of a 50 mg/L copper concentration was absorbed by both O. tritici strain AN4 and O. anthropi strain YX0703 in 150 min. The performance of bacteria in concentrations of 100 and 200 mg/L was also impressive, which indicates the high capacity of these bacteria in the biosorption of copper. Therefore, by providing optimal growth conditions, the potential of this group of bacteria can be used to reduce heavy metal pollution in the southern aquatic ecosystems, especially in areas that are heavily influenced by human activities. Moreover, Generally, the obtained results depicted the possibility of using these bacteria to treat wastewater contaminated with heavy metals.