细菌可使果蝇避免营养不良

Microbes, small and ancient life forms, play a key role in maintaining life on Earth. As has often been pointed¹ 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 nutritional² disorders³ such as protein malnutrition⁴.   Using fruit flies -- Drosophila melanogaster -- as a simple and easily studied stand-in for humans, these new findings advance our understanding of the fundamental mechanisms⁵ underlying⁶ microbial contributions to metabolism⁷ 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 isolated⁸ from field-caught fruit flies, promotes nutritional harvest that rescues the health and longevity⁹ of undernourished flies.   Surprising Protein Harvest   Using a range of radioisotope-labeled dietary components¹⁰ such as amino acids (the components of proteins and the basic building blocks of the body) and sucrose (sugar) to measure the transfer of nutrients¹¹ 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, essentially¹² returning them to the pre-malnutrition profile of well-fed flies.   "Ryuichi and colleagues did a lot of painstaking¹³ 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."