Saccharomyces yeasts are intensively studied in biological research and in their domesticated roles in brewing and baking, and yet, remarkably little is known about their mode of life in forest soils. We report here that resident genotypes of the yeast S. paradoxus are persistent on a time scale of years in their microhabitats in forest soils. We also show that resident genotypes can be replaced by transplanted yeast genotypes. The high inoculum levels in experimental transplantations rapidly decreased over time, but the transplanted genotypes persisted at low abundance. We conclude that, in forest soils, Saccharomyces yeasts exist at very low abundance and that dispersal events are rare.
Background and objectives
The probiotic Escherichia coli strain Nissle 1917 (EcN) has been shown to effectively prevent and alleviate intestinal diseases. Despite the widespread medical application of EcN, we still lack basic knowledge about persistence and evolution of EcN outside the human body. Such knowledge is important also for public health aspects, as in contrast to abiotic therapeutics, probiotics are living organisms that have the potential to evolve. This study made use of experimental evolution of EcN in an insect host, the red flour beetle Tribolium castaneum, and its flour environment.
Methodology
Using a serial passage approach, we orally introduced EcN to larvae of T. castaneum as a new host, and also propagated it in the flour environment. After eight propagation cycles, we analyzed phenotypic attributes of the passaged replicate EcN lines, their effects on the host in the context of immunity and infection with the entomopathogen Bacillus thuringiensis, and potential genomic changes using WGS of three of the evolved lines.
Results
We observed weak phenotypic differences between the ancestral EcN and both, beetle and flour passaged EcN lines, in motility and growth at 30 °C, but neither any genetic changes, nor the expected increased persistence of the beetle-passaged lines. One of these lines displayed distinct morphological and physiological characteristics.
Conclusions and implications
Our findings suggest that EcN remains rather stable during serial passage in an insect. Weak phenotypic changes in growth and motility combined with a lack of genetic changes indicate a certain degree of phenotypic plasticity of EcN.
Lay Summary
For studying adaptation of the human probiotic Escherichia coli strain Nissle 1917 we introduced it to a novel insect host system and its environment using a serial passage approach. After passage, we observed weak phenotypic changes in growth and motility but no mutations or changes in persistence inside the host.
Probiotics are living microorganisms that are increasingly and successfully used for the therapy of various diseases. The most common use of probiotics is the therapeutic and preventive application for gastrointestinal disorders. The probiotic Escherichia coli strain Nissle 1917 (EcN) has been proven to effectively prevent and alleviate intestinal diseases, including various types of inflammatory bowel disease. Despite the widespread medical application of EcN, the underlying mechanisms of its protective effect remain elusive. The present work aimed to establish an insect model system to enable further research on the modes of action of EcN and the dynamics of adaptation to a novel host organism. Using a long-term serial passage approach, we orally introduced EcN to the host, the red flour beetle Tribolium castaneum. After multiple cycles of intestinal colonization in beetle larvae, several attributes of the passaged replicate lines were assessed. We observed phenotypic changes in growth and motility but no genetic changes in the lines after passaging through the host and its flour environment. One of the EcN lines exposed to the host displayed peculiar morphological and physiological characteristics showing that serial passage of EcN can generate differential phenotypes.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.