Antibacterial and Antioxidant Potential of Cadmium-Resistant Halotolerant Bacteria Isolated from Mangrove Rhizosphere Soils in Saudi Arabia
DOI:
https://doi.org/10.22317/jcms.v12i2.2139Keywords:
Halotolerant, Uropathogens, Cadmium, Halomonas, Vreelandella, Anti-Bacterial Agents, AntioxidantsAbstract
Objective: This study aimed to isolate halotolerant and halophilic bacteria and study their abilities to resist cadmium (Cd) and to produce antimicrobial and antioxidant agents.
Methods: Soil samples of mangroves were collected from four different sites in Saudi Arabia: three in Tarut Bay (Darin Safwa, and Syhat) and the fourth in the Farasan Islands (Sajid Island).
Results: Of the 125 isolates obtained on three different media containing 3 M NaCl and 100 ppm Cd (II), Luria-Bertani (LB), saline nutrient, and casein agar, LR40 and LD57 were the most resistant to cadmium metal. The previous isolates grew well for 5 days on LB medium at 37°C in the presence of Cd (II) metal (50-500 ppm at 3 M NaCl), with a minimum inhibitory concentration (MIC) of 600 ppm for both isolates. The two isolates were identified as Vreelandella alkaliphila strain LR40 (accession number PP767765.1) and Halomonas smyrnensis strain LD57 (accession number PP767765). The effect of several factors on the growth of isolates LR40 and LD57 in the presence of Cd (II) metal (300 ppm) was studied; the results showed that the best growth of both isolates in the presence of the metal was at pH 7, 3 M NaCl, 37°C, and after 2 days. The biosorption capacity of Cd (II) by the live biomass of isolates LR40 and LD57 in the solution with 500 ppm was 70.34% and 72.85%, respectively. The ethyl acetate extracts of the two isolates exhibited moderate antibacterial activity against uropathogenic bacteria, and the presence of cadmium in the growth medium enhanced this activity. Also, the cell and ethyl acetate extracts showed excellent antioxidant activity as determined by DPPH (1,1-Diphenyl-2-picrylhydrazyl), with antioxidant percentages ranging from 65-76%.
Conclusion: The coastal mangroves of Saudi Arabia are rich with new halotolerant bacteria that possess a specific combination of resistance to cadmium, tolerance to high salt, and, importantly, antimicrobial and antioxidant activities, making them highly promising candidates for many biotechnological applications
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