Making Choices

How microbes choose lifestyles gives clue to origin of multicellular life

How microbes choose lifestyles gives clue to origin of multicellular life.

Like many bacteria, the Bacillus subtilis lives a double life.

During adventurous phases, the microbes are free-swimming, independent explorers, searching for rare nutrient-rich niches amid an otherwise inhospitable environment. In more communal moments, B. subtilis cells trade their rotating flagellum for an extracellular matrix that causes them to stick together in chains that cling to nearby surfaces. These chains can eventually become the foundation for biofilms, dense communities of microbes that can grow on almost any moist or wet natural or industrial surface.

Though the two lifestyles are well known to microbiologists, the factors guiding the decision of when to choose each state have remained mysterious. Do the cells pick a lifestyle on a whim, or do they retain some memory of the past that influences what they do next?

Researchers led by Johan Paulsson, an associate professor of systems biology at Harvard Medical School, and Richard Losick, the Maria Moors Cabot Professor of Biology in the Harvard Faculty of Arts and Sciences, have developed new tools and techniques that allowed them to discover that random fluctuations in gene expression help drive the initiation of the sedentary communal state, and that the individual cells that make up these nascent colonies share an internal clock that commits them to communal life for an extended “trial period.” The researchers said that these findings provide important insight about how individual cells can organize themselves into a cooperative community, an important first step in the development of multicellular life. The results of the study were published in Nature.