Starving bacteria seek food together

When they're starving, they're social. And when they're social, they're slimy. Bacteria are the centerpiece of new research that has disclosed some of the methodology behind the social organization of bacteria.

The research was conducted in the labs of physics professor Robert Austin and molecular biology professor Jeffry Stock.

Contrary to the past assumption that bacteria disperse randomly and then cluster, this research suggests that the bacteria "can actively find each other," said Peter Wolanin, a postdoctoral researcher in Stock's lab.

Emil Yuzbashyan, a graduate student theorist, observed that when he placed E. coli in microscopic silicone mazes, the bacteria began congregating when placed in confined spots.

However, such an observation would be "hard to qualify," said Sungsu Park, a postdoctoral researcher in Austin's lab and the first author of the paper, which appeared in the July issue of Science.

To more easily validate Yuzbashyan's results, Park designed a simpler maze, using the same microfabrication method used by Yuzabashyan. The modified labyrinth of sorts had a small opening in the center leading to an enclosed area into which the bacteria entered and were observed clustering.

The hypothesis was validated again when the researchers used marine bacteria V. harveyi, which begins to glow once it clumps together with many others of its kind.

A mutant bacteria, whose genome was altered to prevent the bacteria from picking up on relevant chemical signals, did not aggregate as the other bacteria did, indicating chemical signals were behind the clustering.

The clustering bacteria moved into gatherings in a premeditated-like manner through the use of chemotaxis, in which the organism moves along a chemical concentration gradient. The chemical attractants that bacteria follow can be, for instance, amino acids.

Bacteria follow the chemical attractants in a process called a biased random walk, Wolanin explained. Organisms with no outside influence will randomly move about while staying within the confines of the same average area. However, in a biased random walk, organisms will spend a longer period of time moving in the direction of the attractant and a shorter time moving away from it. Therefore, the net motion is in the direction of the attractant.

Chemotaxis is used primarily for dispersing and finding food, scientists thought.

In these experiments, however, the bacteria used chemotaxis when they began to starve, and instead of dispersing to find new food sources, they all clustered in order to seek food out together.

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Previous research did not see this behavior because scientists generally kept their bacteria well fed.

In natural conditions, however, there is no experimenter providing a readily available food source. In this new study, the bacteria were allowed to starve and exhibit their natural instincts of finding each other.

Once the bacteria clumped together, they take part in a collective effort to find the nutrients they need. After they aggregate, the bacteria actually change their physiology to form a protective, adhesive gel-like biofilm.

While the applications of this research may not seem obvious, learning about this social behavior could actually help prevent illness.

The biofilm makes the bacteria resistant to antibiotics, which could make bacterial infections more difficult to control.

Plaque — the type that causes tooth decay — is a form of biofilm.

Biofilms also cause product contamination and equipment failure.

Interfering with the process of chemotaxis could prevent biofilm from forming and thus could be the basis of new ways to deal with the unwanted effects of bacteria.

So, bacteria are still considered infectious and icky. But, through this research, at least we now know they're congenial about it.