Microbial participation in iodine volatilization from soils

Area of Science:

• Environmental Microbiology
• Biogeochemistry
• Soil Science

Background:

• Microorganisms play a significant role in the transformation and cycling of elements within soil ecosystems.
• Iodine's biogeochemical cycle is not fully understood, particularly the mechanisms of its volatilization from terrestrial environments.

Purpose of the Study:

• To investigate the role of soil microorganisms in the volatilization of iodine from soils.
• To identify the specific microbial species and pathways involved in iodine methylation and emission.

Main Methods:

• Incubation of soils with iodide ions and analysis of volatile organic iodine species using gas chromatography.
• Use of radioactive iodine tracers (125I) to quantify iodine emission.
• Isolation and characterization of iodine-volatilizing bacterial strains and phylogenetic analysis based on 16S ribosomal DNA sequences.

Main Results:

• Iodine was primarily emitted as methyl iodide (CH3I), with emission enhanced by glucose and yeast extract.
• Microbial activity was essential, as autoclaving inhibited iodine emission, while antibiotics targeting bacteria (streptomycin, tetracycline) strongly reduced it.
• Fourteen out of forty isolated bacterial strains demonstrated significant iodine volatilization capabilities.
• Phylogenetic analysis revealed that these iodine-volatilizing bacteria are widely distributed across the bacterial domain.

Conclusions:

• Soil bacteria are key agents in methylating and volatilizing iodine as CH3I.
• Iodine-volatilizing bacteria are ubiquitous in soil environments.
• Understanding these microbial pathways is vital for the biogeochemical cycling of iodine and managing radioactive iodine (129I) in the environment.