Recombinant Rhizobium meliloti strains with extra biotin synthesis capability

Area of Science:

• Microbiology
• Plant-Microbe Interactions
• Molecular Biology

Background:

• Biotin is essential for Rhizobium meliloti 1021 growth in alfalfa (Medicago sativa L.) rhizosphere.
• Biotin limitation can restrict R. meliloti 1021 populations in planta.

Purpose of the Study:

• To engineer R. meliloti strains for enhanced biotin production to overcome growth limitations.
• To assess the in vitro and rhizosphere performance of biotin-overproducing R. meliloti strains.

Main Methods:

• Conjugation of the Escherichia coli biotin synthesis operon into a biotin auxotroph R. meliloti 1021-B3 strain.
• In vitro growth assays and cell density measurements.
• Rhizosphere competition experiments comparing engineered strains with wild-type R. meliloti 1021.

Main Results:

• Transconjugant strains (Rm1021-WS10, Rm1021-WS11) exhibited faster in vitro growth and higher cell density.
• Engineered strains overproduced biotin on a defined medium.
• Rm1021-WS11 showed a significant viability loss (up to 99%), while Rm1021-WS10 exhibited reduced cell death, suggesting a stabilizing factor.
• Recombinant strains demonstrated delayed growth and poor competitiveness against wild-type R. meliloti 1021 in alfalfa rhizosphere.

Conclusions:

• Engineering R. meliloti for enhanced biotin synthesis can improve in vitro growth but does not guarantee improved rhizosphere competitiveness.
• Potential viability issues and competitive disadvantages need to be addressed for successful application of engineered R. meliloti in symbiosis.
• Further research is needed to identify stabilizing factors and improve rhizosphere performance of modified R. meliloti strains.