RIVERSIDE — Symbiotic bacteria, which thrive on all plants and animals, are a key yet poorly understood facet of our natural world. Living in symbiosis with their hosts, these bacteria perform a variety of useful functions, such as processing or “fixing” gaseous nitrogen into forms usable by plants and helping break down fibrous foods in the digestive tract of animals.

The evolution of these particular bacteria is the focus of a free, public lecture at the University of California, Riverside on Thursday, Nov. 12. Biologist Joel Sachs will give the hour-long lecture, titled “The Silent Majority: How Symbiotic Bacteria Evolve to Help and Hurt,” at 7 p.m. in the University Theatre. Doors open at 6 p.m. Seating is open.

In his talk, Sachs, an assistant professor at UC Riverside who investigates basic questions about microbial evolution and ecology, will explore the idea that we live in a world surrounded by microbes and explain the dominant roles that symbiotic bacteria play in our lives.

"Each of our bodies is literally covered — both inside and out — with bacteria that help make us what we are," he said. "These bacterial symbionts help us in ways we are just beginning to understand. In the talk, I will describe the key symbioses that biologists study and what we have learned from these natural systems. I will link symbioses to medical research on pathogenic disease."

In the lecture, Sachs also will explain why bacteria are thought to help or hurt their hosts and describe the different evolutionary pathways that symbiotic bacteria can take. At UC Riverside, he studies beneficial bacterial infections as well as how hosts can exert control over bacterial infections and select good bacteria over bad ones.

"Biologists are discovering that these bacterial infections are often evolutionarily unstable and more dynamic than previously thought," Sachs said. "My lab investigates the forces that shape bacterial cooperation with hosts as well as the origins and evolution of harmful strains. We also study the ecological conditions and molecular mechanisms that allow bacteria to undergo switches between being beneficial to being pathogenic."

His lecture is hosted by the College of Natural and Agricultural Sciences and the Science Circle, a group of university and community members committed to advancing science at UC Riverside and in inland Southern California.

It is the last of three talks in the series, "The Science of Evolution II: Applying Evolutionary Ideas." The lectures, which aim to boost the public’s awareness and understanding of how science works and break down some of the misunderstandings about what scientists do, follow an earlier series of lectures on evolution held this year at UC Riverside.

Sachs received his Ph.D. in 2004 from the University of Texas, Austin, and went on to UC Berkeley where he received a National Institutes of Health Ruth Kirschstein National Research Service Award. He joined UC Riverside in 2007.

For more information about the lecture series, visit www.cnas.ucr.edu/sciencelectures/, call (951) 827-6555 or e-mail carol.lerner@ucr.edu.

The University of California, Riverside, is a doctoral research university, a living laboratory for groundbreaking exploration of issues critical to inland Southern California, the state and communities around the world. Reflecting California's diverse culture, UC Riverside's enrollment of about 18,000 is expected to grow to 21,000 students by 2020. The campus is planning a medical school and has reached the heart of the Coachella Valley by way of the UC Riverside Palm Desert Graduate Center. The campus has an annual statewide economic impact of more than $1 billion. To learn more, call (951) UCR-NEWS.