After more than 50 years at Harvard, celebrated molecular biologist Richard Losick has officially closed his MCB laboratory —a quiet but significant milestone in an extraordinary career marked by scientific innovation, influential mentorship, and deep-rooted commitment to teaching.
“I was lucky,” Losick says, reflecting on a career that began in the late 1960s and has helped shape the fields of bacterial cell biology and gene regulation. “It was a glorious era, and I lived through it.”
A Career Forged in a Golden Era
Losick arrived at Harvard from MIT in 1969 as a Junior Fellow of the prestigious Society of Fellows. The nomination came by way of Salvador Luria, a future Nobel Laureate, who had a big influence on Losick when he was a graduate student. James Watson was a Senior Fellow at the time and Luria had been Watson’s PhD mentor. “The fix was in,” Losick jokes. “Watson had to accept me, however unworthy I was.”
He quickly found himself on the third floor of the Bio Labs—a space that would become legendary—working in the lab of Jack Strominger. Losick credits Strominger, who just celebrated his 100th birthday, with launching his career at Harvard and playing a central role in advocating for him during his early years at the university. “He is my scientific hero and a dear friend,” Losick adds.
“The third floor became like an incubator for Nobel Laureates,” he recalls, and writes in a recent essay on the topic. “At one point, there were 10 people who either did Nobel Prize–winning work or trained there.” Among them were George Wald, Wally Gilbert, Robert Horvitz, Mario Capecchi, Richard Roberts, and Victor Ambros, who was most recently awarded the Nobel in 2023.
Coming of scientific age in the presence of Watson and Gilbert had an indelible impact on Losick’s approach to research. It was a straight-talking environment that prized asking questions with complexity yet communicating with clarity, a skill he started to hone while an undergraduate and that he emphasizes to this day. He credits his senior thesis mentor at Princeton, Charles Gilvarg, with teaching him the value of critical feedback in science, and who recommended he do his graduate work with Phillips Robbins at MIT. Robbins worked alongside his lab members at the bench, an experience Losick recalls with great appreciation.
Spore Formation
Early in his career, Losick focused on gene regulation in Bacillus subtilis, using this model organism to study how a bacterial cell differentiates into a dormant spore. This work uncovered how sigma factors—proteins that direct RNA polymerase to specific sets of genes—act in a cascading fashion to regulate developmental transitions. These insights laid a conceptual foundation for understanding how cells adopt specialized roles.
“It was very rewarding,” he says of those early breakthroughs. “It showed how a bacterial cell divides asymmetrically and gives rise to two daughters that have different gene expression programs.” The smaller daughter cell becomes the spore, and the larger daughter cell nurtures it. “That was one of the first examples of how cells specialize.”
Losick was also drawn to studying spore formation in a fascinating, filamentous bacterium called Streptomyces coelicolor.
Together these findings pulled him deeper into bacterial cell biology, a field that, at the time, was just beginning to recognize the spatial organization of bacterial cells. “People used to think of bacteria as just a bag of proteins,” Losick explains. “But we could show that proteins go to specific places inside the cell—just like in higher organisms.”
Biofilm formation
In the 2000s, Losick’s attention turned to an even more socially complex behavior: biofilm formation. Biofilms are surface-associated communities where bacteria embed themselves in a self-produced matrix of extracellular materials. These structures can be highly resilient, enabling bacteria to resist antibiotics, desiccation, and immune responses.
“The idea that bacteria could organize themselves into multicellular communities with distinct cell types and spatial organization—it was just fascinating,” Losick says. “And Bacillus subtilis turned out to be a spectacular model for studying this.”
What began as a line of inquiry into a single cell type morphed into a deep exploration of bacterial collectives. In a series of landmark papers, Losick’s lab and that of his collaborator, Robert Kolter at Harvard Medical School, revealed that biofilms are not just random aggregations but exhibit division of labor among subpopulations of cells. Some cells produce extracellular matrix components. Others generate surfactants to aid in colony expansion. Still others enter a dormant state, acting as a hedge against future environmental stress. “In a way, biofilms are the closest thing bacteria come to having tissues,” Losick explains. “It’s not unlike how cells in a developing embryo adopt different fates to contribute to the overall organism.”
Noise in development
One other theme in Losick’s research was noise, or random fluctuations.[AM1] [LRM2] His early education in biology led him to believe that development is always deterministic. But his work with B. subtilis led him to notice that the bacterium spontaneously switches between a single-cell, motile state and chains of non-motile, sticky cells. This switching takes place under constant environmental conditions and hence is stochastic.
Losick interprets this switching as bet-hedging since the bacterium cannot predict the future. In other words, the non-motile chains exploit the current environment whereas the motile cells swim off to find and exploit new environmental niches. A wonderful collaboration with Johan Paulsson at Harvard Medical School led to the discovery that the source of noise is stochastic competition between just two proteins. It is now widely appreciated that stochasticity is a widespread feature of cell fate determination. For example, when B. subtilis divides asymmetrically to produce a spore, the choice of the pole at which a septum forms is determined by chance. In the compound eye of the fruit fly, Drosophila, the distribution of different types of photoreceptor cells is governed stochastically rather than being programmed.
The Last Chapter and Its Future Implications
B. subtilis is a harmless, soil bacterium. In a “final chapter” of his lab’s scientific output, Losick switched his focus to the biofilm-forming, human pathogen, Staphylococcus aureus. To his surprise, his lab’s work revealed that S. aureus produces biofilms in a very different manner than its distant cousin, B. subtilis in which cells are held together by an electrostatic net composed on DNA. His group’s work paved the way for others to design strategies for disrupting biofilm formation by the pathogen.
“I never imagined when I started in molecular biology that I’d end up studying the social behavior of a pathogen,” Losick reflects. “But the science led me there,” nodding to the sense of closure that has come with winding down his lab.
A Lab That Launched Generations
Over the course of five decades, Losick mentored an estimated 50 graduate students and several scores of postdoctoral fellows. “Maybe a hundred people or more passed through the lab,” he says. Many of them have gone on to distinguished academic and industry careers, continuing the legacy of rigorous inquiry and curiosity-driven science that Losick modeled.
Losick’s era of research also benefitted from a funding environment unlike what many young scientists face today. “I could take chances and go in new directions,” he says, noting that freedom to explore is increasingly rare. “It makes me sad for all my younger colleagues, especially the new ones, or young people who want to enter the field.”
Reinventing the Classroom
Though his lab has closed, Losick isn’t stepping away from Harvard—or from science or teaching.
“I always thought that being a teacher made me a better scientist because it forced me to think about things in a broad context,” he says. “Explaining it to students had a positive impact on my thinking about my own research. And conversely, I would like to think that my being a scientist made me a better teacher because I lived in the practice.”
After decades of teaching freshman and sophomores molecular biology, he has launched a new course on the history of molecular biology—an opportunity to share the story of a field whose history he witnessed first hand. “Since I’m old enough to have lived through the revolution in our understanding of how living things work,” he says with a laugh, “I thought I’d teach it.”
The course is accompanied by an open-access eBook that Losick is in the process of releasing. “It combines classic publications with narrative history,” he says. In Spring 2025, Losick taught the course abroad at the University of Warwick in England,plans to return to Harvard to teach it again this fall, and then teach it at the University of Texas Southwestern Medical Center[AM3] [LRM4] next Spring.
Losick also co-teaches a popular graduate seminar, MCB 208 – Talking About Science – with MCB colleague Jeff Lichtman. In this course, students present and critique landmark Nobel-winning studies. “The whole course is about giving a talk,” he explains. “They pick a Nobel Prize–winning paper and then we take them apart—and build them back up again.”
Has any student ever chosen one of Losick’s own papers? “No,” he says with a chuckle. “I don’t have a Nobel Prize.”
The Third Floor—and Beyond
Losick remains deeply connected to the community that once thrived on the third floor of the Bio Labs, now being echoed in the vibrant work of today’s scientists on the second floor. He attends group meetings and informal gatherings with younger faculty and continues to be inspired by the energy of the next generation.
“The third floor was a special place,” he says. “It wasn’t just the science. It was a community. And that spirit continues.”
The story of the third floor—and Losick’s place in it—has been documented in an essay he wrote for the MCB website, detailing the emergence of molecular biology at Harvard and its remarkable concentration of talent. His personal history even includes an unexpected connection to fellow Nobel Laureate George Wald, whose lecture on death he attended as an undergraduate. “Little did I imagine that a few years later, he’d be my neighbor on the third floor.”
A Life in Science—and Family
While he continues to teach and write, Losick also treasures his time with family, including five grandchildren. He and his wife, Jan Per, who once showed him around Watson’s lab when she was a graduate student, retreat to a remote cabin in northern Maine whenever they can. “We try to spend time with family,” he says simply. “That’s the most important thing.”
As he reflects on his legacy, Losick remains humble. “I’m proud of what I’ve done,” he says. “But it doesn’t merit a trip to Sweden.”
Still, for those who’ve worked with him, studied under him, or been inspired by his decades of work, there’s no doubt that Rich Losick’s impact on molecular biology—and on Harvard—will endure for generations.
August, 2025