Microbial link between arsenic in soil, lower rice yield uncovered, Pg11

Key Highlights:

• Research indicates that the balance of microbes in rice paddies affects arsenic buildup in rice grains, leading to crop losses.
• Arsenic-methylating bacteria convert inorganic arsenic into toxic organic forms, while demethylating archaea reverse this process.
• Straighthead disease, resulting in up to 70% yield losses, is linked to the dominance of arsenic-methylating bacteria in younger soils.
• The study identified 11 methylating microbes and 6 demethylating archaea as predictors of arsenic risk.
• Newly cultivated paddy regions are more vulnerable to straighthead outbreaks due to high ratios of methylating to demethylating microbes.
• Draining rice fields midseason and silicon fertilisation can mitigate risks associated with arsenic uptake.
• Current food safety regulations need to monitor arsenic speciation, not just total arsenic levels.

Detailed Insights:

• Arsenic speciation, the chemical form arsenic takes in soil and plants, is crucial because it determines the extent of straighthead disease.
• Soils younger than 700 years are dominated by arsenic-methylating bacteria, leading to higher accumulation of DMA and DMMTA.
• The ratio of methylating to demethylating microbes exceeding 1.5 significantly increases the risk of straighthead disease.
• Climate change, with higher temperatures and altered flooding, may increase soil arsenic content and disrupt microbial balance.
• Agronomic interventions like draining fields and crop rotation can help manage microbial communities and reduce arsenic uptake.
• Monitoring arsenic speciation, including methylated species like DMMTA, is essential for effective food safety regulations.
• Newly established or reclaimed paddy fields in India may face higher arsenic risk due to microbial imbalances.

Scientific/Technical Concepts Involved:

• Arsenic Methylation: Conversion of inorganic arsenic to toxic organic forms by bacteria.
• Arsenic Demethylation: Breakdown of methylated arsenic compounds by archaea.
• DMA (Dimethylarsinic acid): A toxic organic form of arsenic absorbed by rice plants.
• DMMTA (Dimethylated monothioarsenate): A more toxic derivative of DMA.