Study: Taxonomy, tissue, and habitat influence mollusk microbial communities (DOI: 10.1093/ismejo/wrag092)
A mollusk's microbial community has more to do with its family tree than its address.
In other words, the composition of a mollusk's microbiome depends less on the environment in which it lives and more on what species it belongs to, say University of Michigan researchers.
A microbiome is the collection of bacteria, archaea, viruses and fungi living on and inside hosts, and it's important in helping organisms digest food or protect themselves against harmful microbes.
U-M researchers led by graduate student Diana Vergara-Flórez conducted a review of 85 studies to examine the making of mollusk microbiomes. Their review results mean that two members of the same species of clam will have more similar microbiomes in their guts, even if one lives in a lake in Michigan and one lives in a lake in Europe, than two clams that are of different species but which live in the same lake.
"For the drivers of microbiome differences, who you are matters. Your family matters more than where you live," Vergara-Flórez said. "The environment doesn't matter as much as who you are, or your identity, or your family."
Like humans' gut microbiome, the mollusk microbiome helps them digest food and protects them against harmful microbes, but scientists don't know much about how the mollusk microbiome is composed. Understanding the mollusk microbiome is important to prevent mollusk populations from dying off in a rapidly changing and warming world.
"Each animal has specific microbes that are adjusted to not only specific conditions in the animal, but also where the animal lives," Vergara-Flórez said. "If we make a little change in where the animal lives, let's say, if we pollute their environment or increase its temperature, it can create something we call dysbiosis."
Dysbiosis occurs when beneficial bacteria in the gut decrease and harmful ones increase, potentially leading to illness.
"Microbes can reproduce very fast and can adjust to different environments," said Vergara-Flórez, a doctoral candidate in the U-M Department of Ecology and Evolutionary Biology. "But some of these mollusks may die because their microbial communities change too quickly for the mollusk to adapt."
To examine the make-up of microbiomes in mollusks, U-M researchers reviewed studies that examined three groups of mollusks: gastropods, which include snails and slugs; cephalopods, which include octopuses and squids; and bivalves, which include clams, oysters and mussels.
"Environment, diet and geographical variables matter, but DNA and family matter a bit more for these mollusks," Vergara-Flórez said. "We don't know why microbiome composition seems to be tied to family, but we do know that microbes and their hosts have evolved together for a long time. We call this 'host filtering'-the animal takes the microbes they need from the environment."
The researchers also analyzed which mollusk groups the studies focused on, and found that most of the studies focused on mollusks we eat, such as oysters, mussels and clams. They also found that most of the research was concentrated in the United States, Europe and China.
They say their study highlights the need for more research to better understand and predict the response of mollusk microbiomes to environmental change.
"There isn't much research in this group of animals, even though they have been living on the planet for millions of years. Much of the research that is done has been in the species we consume," Vergara-Flórez said. "We have more than 8,000 species of mollusks, and we know about just a few of them, so it's sad and frustrating how the research is so human-centered."
Vergara-Flórez is continuing to study microbiomes in mollusks, focusing in particular on cone snails from Cape Verde and the Pacific Ocean. Cone snails are a family of venomous snails consisting of more than a thousand species, living in tropical and subtropical regions. They are important in controlling animals in the reefs in which they live.
The study, funded by the U-M Museum of Zoology, was published in The ISME Journal.
