Scripps Institute. US: Microbes, small and ancient life forms, play a key role in
maintaining life on Earth. As has often been pointed out, without
microbes, we’d die—without us, most microbes would get along just fine. Now, a study by scientists from the Florida campus of The Scripps
Research Institute (TSRI) sheds significant new light on a surprising
and critical role that microbes may play in nutritional disorders such
as protein malnutrition.
Using fruit flies—Drosophila melanogaster—as a simple and
easily studied stand-in for humans, these new findings advance our
understanding of the fundamental mechanisms underlying microbial
contributions to metabolism and may point to long-term strategies to
treat and prevent malnutrition in general.
In the study, published February 12 in the journal Cell Reports, a team led by TSRI biologist William Ja showed that Issatchenkia orientalis,
a fungal microbe isolated from field-caught fruit flies, promotes
nutritional harvest that rescues the health and longevity of
undernourished flies.
Surprising Protein Harvest
Using a range of radioisotope-labeled dietary components such as
amino acids (the components of proteins and the basic building blocks of
the body) and sucrose (sugar) to measure the transfer of nutrients from
food to microbe to fly, the study shows that the microbes first harvest
amino acids directly from the fly’s food sources and then transfer that
protein to the fly—by being eaten.
“Flies in the wild carry microbes to every surface they touch,” said
Research Associate Ryuichi Yamada, who spearheaded the study in the Ja
lab. “As flies land on low-protein fruit, they deposit microbes, which
take up and concentrate the available amino acids. By eating the
microbes, flies gain a much needed source of dietary protein.”
In flies that are fed nutrient-poor diets, this chain of events
restores body mass and protein levels, essentially returning them to the
pre-malnutrition profile of well-fed flies.
“Ryuichi and colleagues did a lot of painstaking work to carefully
show that the simplest explanation for what was happening was correct,”
Ja said. “The direct influence of microbes on fly nutrition is often
overlooked and may be relevant in numerous studies of host-microbe
interactions.”
Natural Symbiosis
This relationship appears to be particularly beneficial for flies.
Devouring the protein-plumped microbes extends fly lifespan during
periods when nutrients are scarce. “In fact, the I. orientalis microbe is commonly found in field-trapped fruit flies,” said Yamada. “That suggests a natural symbiosis.”
Ja believes the study also offers a larger lesson on the partnership
that can occur between microorganisms and their hosts, in addition to
providing information on nutrient harvesting and the potential of Drosophila as a platform for studies of host-microbe relationships.
“While everyone keeps looking for that single magic microbial
metabolite or species, what has been increasingly ignored is the bulk
effect that microbes have on primary metabolism,” he said. “Our study
suggests that diverse [microbial] species could each benefit their hosts
and that their quantity, rather than quality, may be of fundamental
importance.”
In addition to Ja and Yamada, other authors of the study, “Microbes Promote Amino Acid Harvest to Rescue Undernutrition in Drosophila,” are Sonali A. Deshpande, Kimberley D. Bruce and Elizabeth M. Mak of TSRI. For more information, see http://www.cell.com/cell-reports/home
The work was supported by the National Institutes of Health (grants
R00AG030493 and R21DK092735), The Ellison Medical Foundation and the
Glenn Foundation for Medical Research.