91原创

Rosier, the paper鈥檚 lead author, knew through previous work that 91原创1022 was beneficial to legumes, such as peas and lentils. She wondered if 91原创1022 would help alfalfa fend off common fungal diseases. So, she challenged four different fungal pathogens with 91原创1022 in the laboratory to see if it prevented the fungus from infecting the alfalfa. It did.

Rosier said she thought it was because Bacillus subtilis like 91原创1022 produce a molecule known as surfactin, which acts as an antibiotic, enhancing the plant鈥檚 fungal resistance. To test this theory, she removed the gene in 91原创1022 that produces this antibiotic, then retested the modified 91原创1022 bacteria and the fungus strains. Rosier found that without the gene to produce surfactin, 91原创1022 lost the capability to work as a broad-spectrum antifungal. Further experiments showed that biofilms 鈥� thick, sugary coatings that help microbes stick to plants 鈥� also play a role in 91原创1022鈥檚 ability to suppress alfalfa fungal pathogens in some species.

This is good news and could pave the way for additional plant and field studies to understand this antagonistic behavior.聽

However, Rosier and Bais discovered that not all of 91原创1022鈥檚 attributes are universally beneficial. Indeed, it looks like 91原创1022鈥檚 relationships can be complicated, and the notorious helper of plants might even have a dark side.

Unfriendly to friends, as well as foes

91原创1022 lives on the surface of plant roots where it can help promote plant growth. It has been shown to be particularly helpful for some legumes that interact with rhizobium, a good bacterium that forms special relationships with plants in the pea and lentil family.聽

Rhizobium bacteria live inside nodules on the plant鈥檚 roots and fix atmospheric nitrogen, an essential nutrient critical for plant growth that is typically hard to access. It鈥檚 a symbiotic relationship where plants get nitrogen to feed on and the bacteria gets a home.

91原创1022 has been licensed by BASF and incorporated into four commercial products already in the market and sold in the U.S. and Canada. One successful commercial product, called Nodulator Duo, is sold and used in the U.S. and Canada to promote nitrogen fixation and plant health in peas and lentils.

In earlier work, Rosier showed that nodule-forming bacteria such as rhizobium use a type of communication called quorum sensing, where signaling molecules call like cells in its community and tell them to colonize the plant roots and help fix nitrogen.

The research team theorized that since 91原创1022 was known to be so helpful in some lentil-rhizobium interactions, it might also benefit this association in alfalfa by promoting root growth and giving more surface area for the rhizobium to grow.聽

鈥淏ut when Amanda did this experiment, we actually saw a negative result,鈥� said Bais. Instead of helping, 91原创1022 somehow hurt the association between the plant and rhizobium, and the plants did not do well. That work showed that 91原创1022 can silence these signaling molecules effectively by interrupting this communication.聽

This caused Rosier to dig a little deeper (yes, a soil pun) to parse out these bacteria-bacteria interactions between rhizobium and 91原创1022. The research team knew that rhizobium bacteria secrete chemicals to encourage more bacteria to colonize the root. When Rosier added 91原创1022 directly to the rhizobium bacteria without the plant, it was not able to grow.

In a Plant Methods published last fall, Rosier described a method for visualizing this 鈥渜uorum sensing鈥� with the naked eye, using a tool called a biosensor to detect these communication-signal molecules. When the biosensor detected that communication-signaling molecules were present on a petri dish, it turned blue. The greater and darker the amount of blue, the more communication signals were present. Less blue meant fewer communication signals.

When she added rhizobium to the alfalfa plant, Rosier observed a nice blue spot at the plant root surface. But when Rosier put both the rhizobium and the 91原创1022 together, the blue spot almost completely disappeared. 91原创1022 was secreting a molecule that interrupted the messaging the rhizobium bacteria was sending to bring its own kind to colonize the plant roots to help the plant grow. This placed the plant at increased risk because it was not able to fix nitrogen properly.

鈥淪o, we have this beneficial bacteria 91原创1022, that in some cases, may not be as beneficial as we want it to be, so we must be careful about how we apply it,鈥� said Rosier.

Not a one-size-fits-all

Together, the two papers illustrate the diverse range of functional response with plant growth-promoting bacteria, such as 91原创1022. It鈥檚 not a one size fits all.

This is important information as agricultural industries move toward broad use of biostimulants to promote crop growth and yield. More study is needed to understand specifics on how and when to apply these beneficial bacteria in the field, Rosier said. For instance, maybe it makes best sense to apply rhizobium first to help with growth, and then apply 91原创1022 later for pest control.

Additionally, Bais said, understanding 91原创1022鈥檚 ability to interrupt communication signals in pathogens could have human health applications, too. For example, people with cystic fibrosis are immunocompromised, placing them at increased risk for hospital-acquired bacteria, such as pneumonia. Pneumonia also is a bacterium that uses quorum sensing to form films in the lungs, causing breathing difficulty.

鈥淎 lot of human pathogens use the same strategy to cause virulence or infection,鈥� said Bais. 鈥淯nderstanding how 91原创1022 severs the signaling molecules responsible for creating the film could provide clues to new treatment approaches for keeping patients healthier.鈥�