UCSB Scientists Detect Signals Between Microorganisms



UCSB researchers discovered an elaborate form of bacterial communication between Escherichia coli bacterium earlier this year, marking the first observed instance of coordination between bacterial organisms.

The organisms collaborate through a chemical exchange between at least two E. coli bacteria, creating a biofilm to help anchor the microbial colony together and shield it from outside elements. The chemical communication is a modified exchange process originally used to block protein synthesis and kill competing bacteria.

According to molecular, cellular and developmental biology professor David Low, the process requires cooperative input from all affected cells.

“The tRNase comes into a CDI [capacitive deionization] negative cell — the one that doesn’t have immunity — and it digests the transfer RNA, and protein synthesis stops,” Low said. “But it turns out that this tRNase that got injected isn’t active at all unless a protein in the target cell called CysK binds to it. That means that the target cell has to supply a factor in order for it to get inhibited or die. It’s as if this inhibitor cell had to ask permission to kill or inhibit the target.”

Low said researchers were puzzled by the necessity for the cell to provide a component of its own destruction.

“Why ask permission from a target cell to inhibit it?” Low said. “That didn’t make a lot of sense.”

The team discovered some E. coli cells contained an immunity protein forming a ternary complex between itself, the tRNase and the cysK to render the inhibitor harmless. The team also found the bacteria could not form biofilms if either tRNase or

CysK production in the cells was disrupted in E. coli cultures. The results indicated the ternary complex is required for the biofilm’s formation.

Low said the research results indicate the bacteria potentially possess a rudimentary form of communication between individual organisms.

“What we believe now — and we’re starting to accumulate some evidence — is that what this system may really be for is to communicate between themselves,” Low said.

An E. coli lacking the immunity protein would be destroyed by encountering one that did, whereas two cells with the immunity protein could cooperate to start a colony. This ensures E. coli without the immunity are weeded out through the evolutionary process.

Low said understanding how bacteria operate as a group could help scientists develop ways to control microorganisms.

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