The bacteria persuade their squid host to create a less hostile working environment

Bacteria living symbiotically within the Hawaiian bobtail squid may direct the host squid to change its normal gene expression schedule to make a home more inviting, according to a new study published in PLoS Biology by researchers from the University of Hawai’i (UH) at the Mānoa School of Ocean and Earth Science and Technology (SOEST).

Almost every organism and environment hosts a collection of symbiotic microbes, a microbiome, which are an integral component of ecological and human health. In bacteria, small RNA (sRNA) is a key element affecting gene expression in microscopic organisms, however, there has been little evidence that beneficial bacteria use these molecules to communicate with their animal hosts.

In the new study, lead author Silvia Moriano-Gutierrez, a postdoctoral fellow at the Pacific Biosciences Research Center at SOEST, and co-authors found that a specific bacterial sRNA that is typically responsible for quality control of protein production in the bacterium plays an essential role in the symbiosis between Vibrio fischeri and the squid.

The Hawaiian squid recruits V. fischeri to inhabit the squid’s luminous organ, as the bacterium is luminescent and camouflages the squid during its night hunt.

Through RNA sequencing, scientists found in squid blood sRNA sequences that were produced by bacteria inhabiting the light organ and found a high concentration of a specific sRNA within the host cells that coat the crypts where bacteria live.

“The presence of this particular sRNA results in a ‘calming’ the squid’s immune reaction, which will increase the ability for bacteria to persistently colonize host tissue and deliver their beneficial effects,” said Dr Moriano-Gutierrez. . “This work reveals the potential for sRNAs of a bacterial symbiont to not only control its own activities, but also to trigger critical responses that promote peaceful partnership with its host.”

The researchers, including co-author and UH Mānoa graduate student Leo Wu, determined that the bacteria load sRNA into their outer membrane vesicles, which are transported to the cells surrounding the symbiont population in the light organ, reducing activities squid antimicrobials in the right position. .

“It was unexpected to find a common bacterial sRNA that had evolved for a housekeeping function in the bacterium to be specifically recruited into bacterium-host communication during the initiation of symbiosis,” said Dr. Moriano-Gutierrez.

“We anticipate that a host’s recognition and response to specific symbiont sRNAs will emerge as an important new mode of communication between bacteria and the animal tissues they live in,” said Dr. Moriano-Gutierrez. “Other symbiotic RNAs entering host cells have yet to be explored.”