Bacteria Colonies Arrange Themselves Like Human Economies: The Rich Get Richer

A new study on bacteria formation reveals that surface bacteria communities called biofilms tend to organize themselves in a way similar to many modern human economies, in a rich-get-richer pattern. The find could help researchers better understand how to battle infections without the use of powerful drugs.

The study is reportedly the first to identify the strategy by which bacteria form the micro-colonies that become biofilms. Biofilms can be the cause of some lethal infections, and the study shows promise at better understanding bacterial infections resistant to antibiotics.

According to the researchers, bacteria in biofilms behave very differently from free-swimming bacteria. Within biofilms, bacteria change their gene expression patterns and are far more resistant to antibiotics and the body's immune defenses than individual, free-swimming bacteria, because they mass together and are protected by a matrix of proteins, DNA and long, chain-like sugar molecules called polysaccharides. This makes seemingly routine infections potentially deadly.

The researchers used an algorithm to map the movements of the bacteria Pseudomonas aeruginosa, which can cause lethal, difficult-to-treat infections, including those found in cystic fibrosis and AIDS patients.

The bacteria that start the biofilm have no special qualities, but as bacteria move across a surface, they leave some influential markers. "Some of the bacteria remained fixed in position," said Matthew R. Parsek, professor of microbiology at the University of Washington who lead the research. "But some moved around on the surface, apparently randomly, but leaving a trail that influenced the surface behavior of other bacteria that encountered it."

Bacteria arriving later also lay trails, but their movements tend to be guided by the trails from the pioneers. This network of trails creates a process of positive feedback and enables bacteria to organize into micro-colonies that mature into biofilms. By being at the right place at the right time, and by using communally produced polysaccharides, a small number of lucky cells - often ones that come later - become the first to form micro-colonies. Cells in micro-colonies have many survival advantages over other bacteria.

The micro colonies develop in accordance to Zipf's Law, which has been used to describe the phenomenon of a small portion of a population controlling the majority of that population's wealth.

"It turns out bacteria do something similar," said Gerard Wong a bioengineering professor at UCLA. "A small number of bacteria have the best access to the lion's share of communally produced polysaccharides."

Wong said the research may provide insight into how to fight antibiotic-resistant bacteria. "Typically, when we want to get rid of bacteria, we just kill them with antibiotics," he said. "As a result, they develop defense mechanisms and grow stronger. Maybe that's not always the best way to treat biofilms. Perhaps we can regulate bacterial communities the way we regulate economies. Our work suggests that new treatment options may use incentives and communications, as well as punishment, to control bacterial communities."