Improving legume nodulation and Cu rhizostabilization using a genetically modified rhizobia.

Area of Science:

• Environmental microbiology
• Plant-microbe interactions
• Bioremediation

Background:

• Rhizobia-legume symbiosis is a promising tool for rhizostabilization of heavy metal-contaminated soils.
• Developing tolerant and symbiotically effective rhizobia is crucial for this application.

Purpose of the Study:

• To enhance symbiotic properties of arsenic-resistant Ensifer medicae MA11 in copper-contaminated environments.
• To engineer a strain capable of alleviating copper toxicity in Medicago truncatula.

Main Methods:

• Transformed Ensifer medicae MA11 with copAB genes from Pseudomonas fluorescens under the nifH promoter control.
• Evaluated the performance of the engineered strain (E. medicae MA11-copAB) in Medicago truncatula grown in copper-contaminated substrates.

Main Results:

• The engineered E. medicae MA11-copAB strain alleviated copper toxicity, maintaining root/shoot growth, nitrogen content, nodulation, and photosynthetic rates.
• Nodules formed by the engineered strain accumulated twice the copper compared to the wild-type.
• Increased copper accumulation in roots and decreased translocation to shoots by the engineered strain.

Conclusions:

• Engineered E. medicae MA11-copAB enhances copper rhizostabilization in Medicago truncatula, reducing the translocation factor and preventing food chain contamination.
• The nifH promoter-copAB construct is a valuable tool for developing rhizobia for copper rhizostabilization in contaminated soils.