1. Iodide uptake by forest soils is principally related to the activity of extracellular oxidases 
Chris M. Yeager
8/19/2109

2. Iodine – why do we care?

3. Iodine biogeochemistry
Biotic processes are a principal driver of iodine cycling
Microorganisms transform the oxidation state of iodine, principally oxidizing iodide (I-) under aerobic conditions and reducing iodate (IO3-) under anaerobic conditions
Microbes are also capable of accumulating iodine and volatilizing it via formation of small organic-I molecules

4. I- oxidation in soils
Biotic processes are thought to be a primary driver of iodination of soil organic matter under aerobic conditions
Oxidation of I- results in the formation of reactive species, I2 and HOI, that will form covalent attachments to soil organic matter
The organisms and mechanisms involved in I- oxidation in soils are poorly defined
Examined I- uptake by soils collected at two depths (0 -10 and cm) from 5 co-located deciduous and coniferous forests in Japan and United States.
Measured a variety of soil parameters and soil enzyme activities to correlate with 125I uptake.
Evaluated 125I uptake in the presence of biocides and enzyme inhibitors
PRIMARY GOAL: Determine the best measure(s) of the iodide oxidation potential of soils, with a focus on microbial processes

5. Inhibitor studies: 125I- has biological underpinnings
Autoclaving, >93% inhibition
The bactericide, Bronopol, average 61% inhibition (range %)
The antifungal agent, Cycloheximide, caused inhibition of 125I uptake in only two samples
The oxidase inhibitor, sodium azide, average inhibition of 81% (range %)

6. 125I uptake corelates with extracellular oxidase activity
Levels of 125I uptake did vary by site; highest in forest soils from the Nishi-Tokyo forested site
125I uptake was not correlated with forest type (deciduous vs. coniferous) or soil depth
ABTS and L-DOPA measures of extracellular oxidases generally tracked the 125I results
As with 125I uptake, measures of extracellular oxidase activity did not correlate with either soil depth or forest type
Peroxidase activity was quite variable and below the level of detection for many soil samples

7. Best predictors of iodide oxidation in soils
Multivariate analysis revealed measurements of L-DOPA oxidation and Actinobacteria biomass accounted for 75% of the variation in 125I uptake in forest soils from two continents
These results indicate that extracellular oxidases drive 125I oxidation and soil binding under aerobic conditions in forest soils and that enzymes from the Actinobacteria may play a particularly important role. Aromatic soil residues with N moieties may be preferentially targeted.