Synergistic enhancement of heavy metal tolerance and reduction by indigenous bacterial consortia of Pseudomonas putida and Pasteurella aerogenes

Abstract

Effective remediation is needed to reduce environmental and health threats from heavy metal contamination. This work examines the bioremediation capability of a new bacterial consortium from the polluted Tanjaro River: Pseudomonas putida pUoR_24 and Pasteurella aerogenes aUoR_24. Research will evaluate the consortium's ability to reduce copper (Cu), zinc (Zn), and nickel (Ni) concentrations in different environments. The study used microbiological methods to investigate metal tolerance, reduction efficiency, and growth optimization at varied temperatures, salinities, and pH levels. Results demonstrate the consortium's superior metal tolerance, with Minimum Inhibitory Concentrations (MICs) of 8 mM for Cu and 7 mM for Ni. Inductively Coupled Plasma Optical Emission Spectrometry (ICP-OES) showed outstanding metal reduction rates of 84.78% for Cu, 91.27% for Zn, and 88.22% for Ni, exceeding those of individual strains. Based on Scanning Electron Microscopy (SEM) and Energy Dispersive X-ray (EDX) analyses, Cu exhibited the highest weight percentage (3.7%), followed by Ni (0.5%), while Zn was undetectable, suggesting preferential sequestration of Cu and Ni by the consortium. The consortium also displayed robust growth across a wide range of temperatures (20-37°C), salinities (up to 4% NaCl), and pH levels (2-11). These findings show that microbial consortia can establish eco-friendly bioremediation solutions for heavy metal-contaminated settings.

Keywords: Pasteurella aerogenes; Pseudomonas putida; Bacterial consortium; Heavy metal bioremediation; Synergistic interactions.

Fig. 1

(a) Map of Iraq showing the location of the Tanjaro River. (b) Google Earth image highlighting the sampling sites along the river (Google Earth). (c–e) Photographs of polluted areas within the Tanjaro River, depicting waste accumulation, industrial discharge, and foam formation due to contamination.

Fig. 2

Phylogenetic tree showing the phylogenetic relationship of the 16S rRNA sequence of the pUoR_24 strain based on the partial 16S rRNA gene sequence in comparison with closely related sequences in GenBank.

Fig. 3

Phylogenetic tree illustrating the relationships of the aUoR_24 strain’s 16S rRNA sequence, based on a partial 16S rRNA gene sequence compared to closely related sequences available in GenBank.

Fig. 4

Metal tolerance of pUoR_24, aUoR_24, and their co-culture. (a) Cu, (b) Zn, (c) Ni, (d) Spot assay showing bacterial growth on nutrient agar plates with varying metal concentrations after 12 h at 30°C.

Fig. 5

Heavy metal reduction by pUoR_24, aUoR_24, and their co-culture after 24 h of incubation with an initial concentration of 3 mM of Cu, Zn, and Ni. Metal concentrations were determined by ICP-OES. Control samples were prepared without bacterial strains.

Fig. 6

Temperature optimization for bacterial growth of pUoR_24, aUoR_24, and their co-culture in the presence of 3 mM Cu, Zn, or Ni. Growth was measured after a 24 h incubation.

Fig. 7

Effect of NaCl concentration on bacterial growth of pUoR_24, aUoR_24, and their co-culture in the presence of 3 mM Cu, Zn, or Ni. Growth was measured after 24 h incubation at 30°C.

Fig. 8

pH optimization for bacterial growth of pUoR_24, aUoR_24, and their co-culture with and without 3 mM Cu, Zn, or Ni. Growth was measured after 24 h incubation at 30°C.

Fig. 9

SEM analysis of bacterial cells exposed to metals. (a) Cu, (b) Ni, (c) Zn.

Fig. 10

EDX analysis of bacterial cells exposed to metals. (a) Control, (b) Cu, (c) Ni, (d) Zn.