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

Iodine – why do we care?

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

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 10 - 20 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

Inhibitor studies: 125I- has biological underpinnings Autoclaving, >93% inhibition The bactericide, Bronopol, average 61% inhibition (range 7 - 89%) The antifungal agent, Cycloheximide, caused inhibition of 125I uptake in only two samples The oxidase inhibitor, sodium azide, average inhibition of 81% (range 55 - 99%)

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

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.