Researchers reveal the ‘dark side’ of beneficial soil bacteria

September 21, 2012 under CANR News

It’s a battleground down there — in the soil where plants and bacteria dwell.

Even though beneficial root bacteria come to the rescue when a plant is being attacked by pathogens, there’s a dark side to the relationship between the plant and its white knight.

According to research reported by a University of Delaware scientific team in the September online edition of Plant Physiology, the most highly cited plant journal, a power struggle ensues as the plant and the “good” bacteria vie over who will control the plant’s immune system.

“For the brief period when the beneficial soil bacterium Bacillus subtilis is associated with the plant, the bacterium hijacks the plant’s immune system,” says Harsh Bais, assistant professor of plant and soil sciences, whose laboratory group led the research at the Delaware Biotechnology Institute.

In studies of microbe-associated molecular patterns (MAMPs), a hot area of plant research, the UD team found that B. subtilis produces a small antimicrobial protein that suppresses the root defense response momentarily in the lab plant Arabidopsis.

“It’s the first time we’ve shown classically how suppression by a benign bacteria works,” Bais says. “There are shades of gray — the bacteria that we view as beneficial don’t always work toward helping plants.”

In the past, Bais’ lab has shown that plants under aerial attack send an SOS message, through secretions of the chemical compound malate, to recruit the beneficial B. subtilis to come help.

In more recent work, Bais and his collaborators showed that MAMP perception of pathogens at the leaf level could trigger a similar response in plants. Through an intraplant, long-distance signaling, from root to shoot, beneficial bacteria are recruited to forge a system-wide defense, boosting the plant’s immune system, the team demonstrated. In that study, the Bais team also questioned the overall tradeoffs involved in plants that are associated with so-called beneficial microbes.

In the latest work, involving the testing of more than 1,000 plants, the researchers shed more light on the relationship. They show that B. subtilis uses a secreted peptide to suppress the immune response in plants. It is known that plants synthesize several antimicrobial compounds to ward off bacteria, Bais says.

The team also shows that when plant leaves were treated with a foliar MAMP — flagellin, a structural protein in the flagellum, the tail-like appendage that bacteria use like a propeller — it triggered the recruitment of beneficial bacteria to the plant roots.

“The ability of beneficial bacteria to suppress plant immunity may facilitate efficient colonization of rhizobacteria on the roots,” Bais says. Rhizobacteria form an important symbiotic relationship with the plant, fostering its growth by converting nitrogen in the air into a nutrient form the plant can use.

“We don’t know how long beneficial bacteria could suppress the plant immune response, but we do know there is a very strong warfare under way underground,” Bais says, noting that his lab is continuing to explore these interesting questions. “We are just beginning to understand this interaction between plants and beneficial soil bacteria.”

The lead author of the research article was Venkatachalam Lakshmanan, a postdoctoral researcher in the Department of Plant and Soil Sciences; Sherry Kitto, professor of plant and soil sciences; Jeffrey Caplan, associate director of UD’s Bio-Imaging Center; Yu-Sung Wu, director of the Protein Production Facility; Daniel B. Kearns, associate professor in the Department of Biology at Indiana University; and Yi-Huang Hsueh , of the Graduate School of Biotechnology and Bioengineering at Yuan Ze University, Taiwan.

The research was supported by grants from the National Science Foundation.

Article by Tracey Bryant

Animation and images courtesy of Harsh Bais

This article can also be viewed on UDaily.


UD graduate Seyler studies ethnobotany in Hawaii

September 14, 2012 under CANR News

Culturally and botanically, University of Delaware graduate Barnabas Seyler is living in paradise as he conducts his doctoral research in ethnobotany at the University of Hawaii.

Ethnobotany, the blending of ethnology–the study of culture–and botany–the study of plants–suits Seyler perfectly as he loves learning about diverse people, histories and cultures as well as plants. He said that this multidisciplinary approach is important because, “much of the major conservation and botanical challenges we face today are quite complicated, and they, in many cases, must be solved in cooperation/collaboration with people in quite different cultures.”

As an undergraduate at UD, Seyler learned about a wide variety of subjects as he received a bachelor of science from the College of Agriculture and Natural Resources (CANR), double majoring in landscape horticulture and plant science, with a minor in plant biology, and a bachelor of arts degree from the College of Arts and Sciences where he majored in East Asian studies with a minor in philosophy. For his graduate degree, Seyler attended the Longwood Graduate Program in public horticulture where he earned his master of science degree.

Seyler said that he enjoyed the small teacher to student ratio at CANR and “loved that the teachers knew me by name and knew my interests and encouraged me along the way.” He also said that he enjoyed getting to know David Frey, associate professor in the Department of Plant and Soil Sciences, who served as the advisor to the Horticulture Club, of which Seyler was President for 3 years. “Dr. Frey was also always there to offer advice and encourage me along the way,” said Seyler.

Seyler also noted that his academic advisor Sherry Kitto, professor in the Department of Plant and Soil Sciences, was “quite encouraging to me when things got difficult and was always full of wisdom and practical advice.”

Of the Longwood Graduate Program, Seyler said that, “The professional connections and contacts I was able to make, the professional development opportunities, and the incredible travel and research trips were quite significant in leading me to where I am today. My advisor, Dr. Robert Lyons, who is the director of the Longwood Graduate Program, was also a great resource. He allowed me to continue taking Chinese language classes throughout my master’s program, and he was a great encouragement.”

During his master’s program, Seyler traveled to China where he conducted his thesis research, before ending up in Hawaii.

For someone who loves rich, diverse culture and plant life as much as Seyler, he couldn’t have found a better place. “I can’t deny that the weather and tropical flora are quite enjoyable. Although I am actually a temperate-flora guy, I am really enjoying the ability to become better versed in tropical plants,” said Seyler. On the cultural side, Seyler said that what he really enjoys about Hawaii is that it “has an incredibly rich diversity of cultures, languages, and people. Hawaiian Pidgin, the local creole language, is quite interesting since it blends English with the beautiful Hawaiian language, with its deep meaning and cultural significance. As one who loves learning languages and interacting with different cultures, I feel like I am in Heaven!”

At the University of Hawaii, Seyler is conducting his research with a professor in China at Sichuan University. The two of them will work on a population assessment of the orchids in Sichuan Province. Though the project is still in its preliminary stages, Seyler does say that there is a need to assess the current status of orchids throughout China, as many populations have been declining as a result of over harvesting.

In addition to his studies, Seyler is also a teaching assistant for a plant ecology class. He said that he enjoys the class because it is relatively new and thus has a lot of flexibility and potential for the future and that he enjoys being able to work with the professor who he said is “an excellent teacher and well-liked by the students.”

Seyler is also in a unique position as he is both a student at the University of Hawaii and a participant in the East-West Center’s education program. According to its website, the East-West Center promotes better relations and understanding among the people and nations of the United States, Asia and the Pacific through cooperative study, research and dialogue.

Seyler explained that he “received an East-West Center Association Alumni Scholarship, so I participate in the EWC Graduate Degree Program. I get to live in the EWC dormitory with students from all over the Asia Pacific region and beyond.”

He estimates that there are more than 60 countries represented and said that they “participate in educational programs, seminars, and community-building activities together, while also building friendships and relationships that will continue into our careers and future lives.”

For anyone interested in applying to graduate school, Seyler offered some words of wisdom saying, “In my experience, there are three things that graduate schools, and employers, are looking for in applicants–beyond simply the GPA, letters of recommendation, and essays.”

Those three things are “study abroad, volunteer, and internship experiences. If at all possible, I would encourage students to try to get as many of these opportunities as possible.”

Article by Adam Thomas