Research on bacteria adds to understanding of their social life

According to a study, strains of the bacterium Vibrio cholerae transform themselves from small, comma-shaped cells to long filaments in nutrient-poor environments to aid short-term survival.

This strategy of changing cell shape supports the growth of bacterial communities and allows the pathogen to compete in environments with a quick turnover of surfaces on which to grow.

The formation of the elongated cell shapes allowed the rapid formation of communities of bacteria that bind to surfaces, known as biofilms that are essential in turbulent nutrient environments. These formations came at the expense of being able to compete in the long term with biofilms made from smaller cells that pack together more tightly.

The finding added to the understanding of how bacteria adapt to their environment, reported a study published in the journal of Proceedings of the National Academy of Sciences.

"Bacteria are normally thought of as solitary organisms, but they are actually highly-social organisms that like to live in groups. This research shows that we can relate cell structure to group behaviour in new ways when looking at realistic environments," said Carey Nadell, an assistant professor of biology at Dartmouth.

When not inside a human host, V. cholerae grows on nutritious pieces of debris in aquatic environments. This debris, known as chitin, comes from the shells of arthropods like plankton and shrimp. Cholera cell growth on the chitin typically takes place in the form of biofilms featuring clusters of organisms.

In the research, strains of cholera were grown in seawater and then observed using 3D microscopy with the aid of fluorescent markers to make the bacteria visible. The researchers found that the altered long-filaments become entangled, providing an advantage that allows the bacteria to quickly colonize nutrient-rich particles in seawater.

The researchers noted that the formation of the filament-like structure came at the expense of longer-term competitive ability enjoyed by shorter cells that adhere more strongly to each other and to surfaces.

"This has important consequences for how cells survive in the environment. It shows how bacterial cell shape can be coupled to environmental success during the surface occupation, competition within biofilms, and dispersal to new resource patches," said Nadell.

There are many strains of the cholera bacteria. Because the bacteria in the study were grown in seawater, the research does not directly lead to a greater understanding of how cholera acts within the human body.

The discovery of a new way that bacteria form groups on surfaces can, however, help researchers understand more about how bacteria act and associate.