Serial passage in an insect host indicates genetic stability of the human probiotic Escherichia coli Nissle 1917

Schröder NCH, Korša A, Wami H, Mantel O, Dobrindt U, Kurtz J

Abstract

Abstract Background and objectives:The probioticEscherichia colistrain 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 beetleTribolium castaneum,and its flour environment.Methodology:Using a serial passage approach, we orally introduced EcN to larvae ofT.castaneumas 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 entomopathogenBacillus 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 probioticEscherichia colistrain 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.