Bacterial adaptations unveiled: Bradyrhizobium SUTN9-2's responses to plant extracts

New study explores how Bradyrhizobium SUTN9-2 interacts with rice, chili, and tomato, influencing growth and nitrogen fixation.

A groundbreaking study has unveiled unique responses of Bradyrhizobium sp. strain SUTN9-2 when exposed to extracts from various host plants such as rice, chili, and tomato. This bacterium is not only capable of nitrogen fixation but also demonstrates remarkable adaptability through endophytic interactions.

Researchers found SUTN9-2 experiences significant morphological and physiological changes, including cell enlargement and increased DNA content, particularly when interacting with Oryza sativa (rice) extracts. The transformative effects on bacterial cells are believed to stem from interactions with the plant’s cationic antimicrobial peptides (CAMPs), which trigger adaptive responses similar to those seen under symbiotic conditions.

Utilizing advanced transcriptomic and cytological techniques, the scientists revealed notable upregulation of genes linked to CAMP resistance, nitrogen metabolism, and defensive responses when SUTN9-2 was treated with plant extracts. These interactions exhibited variations across different plant species, providing insights on how endophytic bacteria manage the challenges posed by host defenses.

According to the study, "This study suggests SUTN9-2 likely evolves resistance mechanisms against CAMPs found in rice, chili, and tomato plants." This highlights the bacterial strain's potential for improving agricultural sustainability, as it could help crops to thrive under adverse conditions.

Notably, the findings also show SUTN9-2 can colonize both chili (Capsicum annuum) and tomato (Solanum lycopersicum), offering similar benefits to rice, though the degree of effectiveness varied. For example, SUTN9-2 treatment led to significant growth enhancements in tomato plants, with increases of 133% in total length by 28 days post-inoculation (dpi).

While the effects of rice extracts resulted in pronounced cell enlargement and higher nitrogen fixation activity, chili extracts appeared to induce cell death more rapidly, demonstrating the complex dynamics at play during these endophytic interactions. The researchers noted, "Distinct plant factors significantly alter the bacterial cell size and nitrogen fixation efficiency," underlining the need to understand specific plant-bacterial interactions for optimizing biofertilizer effectiveness.

The study also evaluated how the extracts influenced the bacterial viability and nitrogenase activity. Results indicated chi extracts led to significant cell death, correlatively reducing the nitrogen-fixing capabilities of SUTN9-2, unlike the more favorable environment provided by rice extracts, which maximized nitrogenase activity.

Overall, this research not only elucidates the survival strategies of Bradyrhizobium sp. SUTN9-2 but also extends our comprehension of the roles these bacteria play as endophytes across various plant species. "These findings provide insights for enhancing biofertilizer applications," the authors concluded, signaling important steps toward sustainable agricultural practices.