Studying Toxic Microbes in Grasses

By Marlene Cimons, National Science Foundation

“Sleepy grass,’’ which commonly grows in many western states, got its name for a reason.  When livestock graze upon it, they go to sleep. More accurately, they freeze in place.  Some animals even can die.

“They are like statues, they don’t move,’’ said Stan Faeth, professor of biology and head of the biology department at the University of North Carolina, Greensboro. 

All plant species harbor microbial “partners,’’ that is, microbes such as bacteria or fungi that “infect’’ the plant and live within plant tissues. They can dramatically alter plant growth and performance, often in ways beneficial to the plant. Like plant and animal species, microbes also can hybridize and create new genetic species and variants. 

“All organisms have lots of microbes internally,’’ Faeth said. “When microbes hybridize, this can change the processes of the hosts they are living in.’’

Fungal endophytes, for example, which are found in many types of grasses, produce alkaloids which help resist drought and resist herbivores. But, as is the case with “sleepy grass,’’ these alkaloids also can be toxic to animals. 

Faeth and his colleagues, which include Nadja B. Cech, associate professor in the university’s department of chemistry and biochemistry, are trying to better understand the workings of fungal endophytes.

“We’re trying to find out what maintains this remarkable variability in nature--why some are so toxic, and others have no effect at all,’’ Faeth said.

The National Science Foundation is funding the program through $615,971 in grant money, as part of the American Recovery and Reinvestment Act of 2009.

Their research, although basic, could have broad implications for the multi-billion dollar livestock industry, as well as for the restoration of native grasslands and the management of forage grasses.  The knowledge also could help the turf grass industry in the planning and maintenance of recreation areas.  

“The knowledge can be used practically,’’ Faeth said.  “If, for example, you want to restore native grass in a conservation setting, but have no idea whether the grass seeds are infected. So, in that way, it can improve the success of conservation efforts.’’

Moreover, “you can plant grass with high endophytes in places where nothing is grazing, such as golf courses,’’ Faeth continued.   “The grass uses less water and resists insects. It’s good for golf courses, but you don’t want to plant it in pastures where it will make livestock sick.’’

Faeth and his team are conducting greenhouse and field experiments in Arizona on two native grasses:  “sleepy grass’’ and Arizona fescue. The endophytes within Arizona fescue produce alkaloids but, unlike those in “sleepy grass,’’ they don’t hurt livestock.

The research team has been setting up what Faeth described as “common garden experiments’’ to understand how the endophytes work within the plant, and whether changing certain conditions can increase the grass’s ability to survive and compete better in harsh environmental conditions.

“We take plants with different strains of endophytes and grow them,’’ he said. “Then we alter the factors that can change the endophyte effect on the host, such as water, nutrients and competition. The alkaloid production stays the same. We are looking at the plant’s response in terms of growth and reproduction to understand how the plant responds to these variants.  We want to better understand how they (endophytes) work.”

Endophytes are not always good for the plants, he said.  “Depending on the strain of endophyte, you can get varying effects on the plant,’’ Faeth said. “We are studying this as well. Although endophytes generally are thought to be positive  (for the plant), most of our research is showing you can get highly variable effects. It’s important to know what strain you have.’’

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