Hawaiian bobtail squid depend on bacterial partner for healthy development

Contact:

Researchers have found there is a bacterial protein "key" that allows the Hawaiian bobtail squid to develop a healthy body and its bioluminescent "glow." While researchers have long known the squid recruits Vibrio fischeri from the ocean to provide bioluminescent camouflage, a University of Hawai'i at Mānoa study revealed that the benefit of the partnership extends far beyond light-production: the bacteria were found to play a vital role in the healthy development of the squid.

"Our recent work revealed that in order to develop properly, the squid host requires a protein provided by its bacterial symbiont," said Jill (Kuwabara) Smith, lead author of the study, who was a postdoctoral researcher at the Pacific Biosciences Research Center (PBRC) in the UH Mānoa School of Ocean and Earth Science and Technology (SOEST) at the time of this research. "This was very surprising, but given that the work we do with this symbiosis model is always pioneering, just about every new finding is a surprise!"

Most bacteria release tiny, protein-filled "delivery packets" from their surfaces. Researchers previously knew that the Vibrio fischeri bacteria used a specific protein in these packets, called SypC, to start its relationship with the squid.

"Once the bacteria and its vesicles are inside the squid host, the new research found that the SypC assumes a new function-it prompts development of the light-organ itself," Smith shared.

Tracking a rare but important protein

To test this, the team tracked SypC by making it glow under a microscope. They found that without this single bacterial protein, the squid's body did not develop correctly. Interestingly, the squid's own immune cells-which usually kill germs-actually helped pick up these bacterial packets and carry them to the exact spot where the light organ needed to grow. Without SypC, the expression of 138 different genes in the squid was altered.

"In addition to contributing light-production capabilities, Vibrio fischeri are prompting the squid's development of organs and healthy expression of genes that are involved in a wide range of functions," said Smith.

From squid to human health

Nearly every organism and environment hosts a collection of microbes-a microbiome-which are an integral component of health. But the communication between bacteria and host before, during and after the meet-up has been mysterious.

"Very often an animal's microbiome is highly complex, so it is difficult to determine what each bacterial species is contributing to the molecular 'conversation' with the host animal," said Margaret McFall-Ngai, senior author on the paper, Professor Emerita at PBRC, and senior staff scientist at Caltech/Carnegie Science in Pasadena. "The host squid that we study naturally interacts with only one bacterial species, so the exchange between partners is much easier to understand."

Given the small size of baby Hawaiian bobtail squids (only a couple of millimeters long) it is possible to visualize, by confocal microscopy, the effects of host-microbe interactions with great resolution.

"The goal of our research is to discover those features of symbiosis that are evolutionarily conserved, from less complex animals through humans," said Smith, who is now a science teacher at 'Iolani School. "Those elements that are evolutionarily conserved are likely to be very important. Once we discover something, it can provide clues as to how things work in mammalian systems. The squid-vibrio system has guided the biomedical community again and again over the last 35+ years of its study."