Characterization of Mercury-Resistant Rhizobacteria for Plant Growth Promotion: An In Vitro and In Silico Approach

Area of Science:

• Microbiology
• Environmental Science
• Biotechnology

Background:

• Rhizobacteria play a crucial role in plant health and soil ecosystems.
• Mercury contamination poses a significant environmental and health risk.
• Understanding bacterial resistance mechanisms is vital for bioremediation strategies.

Purpose of the Study:

• To screen and characterize rhizobacterial isolates for mercury resistance and plant growth-promoting traits.
• To identify bacterial species with high indole-3-acetic acid (IAA) production and mercuric chloride (HgCl2) resistance.
• To elucidate the structural and functional aspects of the MerB protein involved in mercury detoxification.

Main Methods:

• Screening of 30 rhizobacterial isolates for HgCl2 resistance, growth on nitrogen-free mannitol (NFM), and IAA production.
• Biochemical characterization and 16S rDNA ribotyping for phylogenetic analysis of selected isolates.
• Bioinformatic tools (Protparam, Pfam, I-TASSER, etc.) for structural determination and functional prediction of the MerB protein.

Main Results:

• Six isolates (UM-3, AZ-5, UM-7, UM-11, UM-26, UM-28) showed significant HgCl2 resistance (30 µg/ml) and high IAA production.
• Phylogenetic analysis identified isolates as Exiguobacterium sp., Bacillus thuringiensis, Bacillus subtilis, Enterobacter cloacae, and Pseudomonas aeruginosa.
• Bacillus thuringiensis AZ-5 exhibited high HgCl2 resistance due to the merB gene; MerB protein predicted to be organomercuric lyase involved in Hg detoxification with MerA.

Conclusions:

• Selected rhizobacteria possess valuable traits for mercury bioremediation and plant growth promotion.
• The study identified specific bacterial strains with robust mercury resistance mechanisms.
• Bioinformatic analysis provided insights into the structural homology and function of the MerB protein in bacterial mercury detoxification.