Three bacterial strains efficiently reduce selenite to selenium nanoparticles in cell membranes

Area of Science:

• Microbiology
• Nanotechnology
• Agricultural Science

Background:

• Microbial synthesis of selenium nanoparticles (SeNPs) is key for selenium-rich agriculture.
• Existing selenium-reducing strains have limited selenite tolerance (≤100 mmol/L) and low efficiency.

Purpose of the Study:

• To screen and identify microbial strains with high selenite tolerance and efficient SeNP synthesis capabilities.
• To characterize the selenium-reducing bacteria and their SeNP production mechanisms.

Main Methods:

• Screening of selenium-rich soil for high-tolerance microbial strains.
• Identification of isolates using 16S rRNA gene sequencing.
• Analysis of SeNP synthesis and characterization (size, morphology).
• Quantitative PCR (qPCR) to elucidate selenium reduction pathways.

Main Results:

• Three strains tolerating >300 mmol/L selenite were isolated: Citrobacter sp.BM-1, Providencia sp.BM-2, and Brucella sp.BM-3.
• Brucella sp.BM-3 is identified as a novel selenium-reducing bacterium.
• All strains synthesized spherical SeNPs (210-221 nm) extracellularly.
• The glutathione pathway, involving nitrate and sulfate reductases, was identified as the primary selenium reduction mechanism.

Conclusions:

• Citrobacter sp.BM-1, Providencia sp.BM-2, and Brucella sp.BM-3 are highly effective for microbial selenium nanoparticle synthesis.
• These strains demonstrate significant potential for developing advanced selenium-rich fertilizers.
• The identified novel bacteria expand the toolkit for biotechnological applications of selenium nanoparticles.