Heavy Metal Resistance Ability of Pseudomonas Species Isolated from Sludge and Sewage in Iraq

Document Type : Original Articles


1 Department of Medical Laboratory Techniques, College of Medical Technology, Al-Farahidi University, Baghdad, Iraq

2 Department of Forensic Evidence Techniques, College of Medical Technology, Al-Farahidi University, Baghdad, Iraq


It has been well documented that one of the best ways to remediate water and soil heavy metal pollution would be the use of microorganisms able to absorb heavy metals. The ability to resist toxic and heavy metals has been developed in some bacteria and microorganisms. This study, therefore, aimed to test the resistance ability of Pseudomonas species (spp.) isolated from sludge and sewage in Iraq against heavy metals, including mercury (Hg), copper (Cu), nickel (Ni), and cadmium (Cd) with a minimal concentration of 50 μg/ml for each. Water and soil samples were collected from different locations in Iraq. To test the tubes, 1 ml of each water sample, 1 gm of each soil sample, and 9 ml of sterilized distilled water were added and mixed thoroughly, followed by serial dilutions for each test tube separately. A total of 100 μl of aliquots from the appropriate dilution (10-2) were also cultured on nutrient agar plates and then incubated at 37˚C for 18 h. Different colonies from both water and soil samples were selected and grown on king A and king B media plates to confirm that these types of bacteria belong to the Pseudomonas genus. The isolates were identified based on their staining ability, shape, color, size, production of pigments, transparency, and mucoid properties of colonies growing on nutrient agar plates. In addition, some other biochemical tests were conducted. Several colonies were obtained and selected from the cultured samples and consequently, cultured and purified as a single colony. The preliminary observation and biochemical identification of these isolates indicated that two of them belonged to Pseudomonas spp.: Ps-1(M9) and Ps-2(M19). The screening of the bacteria isolates for resistance against Cu (II), Hg (II), Cd (II), and Ni (II) was performed by the use of Minimum Inhibitory Concentration. During the experiment and screening, different metal levels were evaluated to choose the best bacterial isolates with the ability of normal growth and resistance against heavy metal toxicity. The recorded data showed that two Pseudomonas isolates could tolerate heavy metal concentrations ranging from 50 to 180 μg/ml. Additionally, the two resistant Pseudomonas isolates also showed resistance to some antibiotics.


Main Subjects

  1. Singh P, Purakayastha TJ, Mitra S, Bhowmik A, Tsang DCW. River water irrigation with heavy metal load influences soil biological activities and risk factors. J Environ Manage. 2020;270:110517.
  2. Chi Fru E, Rodriguez NP, Partin CA, Lalonde SV, Andersson P, Weiss DJ, et al. Cu isotopes in marine black shales record the Great Oxidation Event. Proc Natl Acad Sci U S A. 2016;113(18):4941-6.
  3. Pal C, Asiani K, Arya S, Rensing C, Stekel DJ, Larsson DGJ, et al. Metal Resistance and Its Association With Antibiotic Resistance. Adv Microb Physiol. 2017;70:261-313.
  4. Khallef M, Benouareth DE, Konuk M, Liman R, Bouchelaghem S, Hazzem S, et al. The effect of silver nanoparticles on the mutagenic and the genotoxic properties of the urban wastewater liquid sludges. Environ Sci Pollut Res Int. 2019;26(18):18403-10.
  1. Marshall TM, Colvin KL, Nevin R, Macrellis J, Dardia GP. Neurotoxicity Associated with Traumatic Brain Injury, Blast, Chemical, Heavy Metal and Quinoline Drug Exposure. Altern Ther Health Med.2019;25(1).
  2. Mao C, Song Y, Chen L, Ji J, Li J, Yuan X, et al. Human health risks of heavy metals in paddy rice based on transfer characteristics of heavy metals from soil to rice. CATENA. 2019;175:339-48.
  3. Gemeda FT, Guta DD, Wakjira FS, Gebresenbet G. Occurrence of heavy metal in water, soil, and plants in fields irrigated with industrial wastewater in Sabata town, Ethiopia. Environ Sci Pollut Res Int. 2021;28(10):12382-96.
  4. Liu Q, Xu X, Zeng J, Shi X, Liao Y, Du P, et al. Heavy metal concentrations in commercial marine organisms from Xiangshan Bay, China, and the potential health risks. Mar Pollut Bull. 2019;141:215-26.
  5. Williams CL, Neu HM, Gilbreath JJ, Michel SL, Zurawski DV, Merrell DS. Copper Resistance of the Emerging Pathogen Acinetobacter baumannii. Appl Environ Microbiol. 2016;82(20):6174-88.
  6. Rahman Z, Singh VP. The relative impact of toxic heavy metals (THMs) (arsenic (As), cadmium (Cd), chromium (Cr)(VI), mercury (Hg), and lead (Pb)) on the total environment: an overview. Environ Monit Assess. 2019;191(7):419.
  7. Noreen U, Ahmed Z, Khalid A, Di Serafino A, Habiba U, Ali F, et al. Water pollution and occupational health hazards caused by the marble industries in district Mardan, Pakistan. Environ Technol Innov. 2019;16:100470.
  8. Cardoso P, Nunes T, Pinto R, Sa C, Matos D, Figueira E. Rhizobium response to sole and combined exposure to cadmium and the phytocompounds alpha-pinene and quercetin. Ecotoxicology. 2020;29(4):444-58.
  9. Bhuiyan MAR, Khan T, Huq SM. Cadmium and lead tolerant bacteria isolated from industrial waste water. Dhaka Univ J Biol Sci. 2017;26:29-38.
  10. Sher S, Rehman A. Use of heavy metals resistant bacteria-a strategy for arsenic bioremediation. Appl Microbiol Biotechnol. 2019;103(15):6007-21.
  11. Medfu Tarekegn M, Zewdu Salilih F, Ishetu AI. Microbes used as a tool for bioremediation of heavy metal from the environment. Cogent food agric. 2020;6(1):1783174.
  12. Marzan LW, Hossain M, Mina SA, Akter Y, Chowdhury AMMA. Isolation and biochemical characterization of heavy-metal resistant bacteria from tannery effluent in Chittagong city, Bangladesh: Bioremediation viewpoint. Egypt J Aquat Res. 2017;43(1):65-74.
  13. Xing D, Magdouli S, Zhang J, Koubaa A. Microbial remediation for the removal of inorganic contaminants from treated wood: Recent trends and challenges. Chemosphere. 2020;258:127429.
  14. Koedam N, Wittouck E, Gaballa A, Gillis A, Hofte M, Cornelis P. Detection and differentiation of microbial siderophores by isoelectric focusing and chrome azurol S overlay. Biometals. 1994;7(4):287-91.
  1. Gill JS, Arora S, Khanna SP, Kumar KH. Prevalence of Multidrug-resistant, Extensively Drug-resistant, and Pandrug-resistant Pseudomonas aeruginosa from a Tertiary Level Intensive Care Unit. J Glob Infect Dis. 2016;8(4):155-9.
  2. Holt JG, Kreig NR, Williams ST. Bergyy's Manual of Determination bacteriology. 9th ed: Williams and Wilkins; 199.

21.          Garrity G, Bell J, Lilburn T. Taxonomic Outline of the Prokaryotic Genera. Bergey's Manual of Systematic Bacteriology.2003. 397 p.