The Evolution of Host Specialization in the Vertebrate Gut Symbiont Lactobacillus reuteri

Recent research has provided mechanistic insight into the important contributions of the gut microbiota to vertebrate biology, but questions remain about the evolutionary processes that have shaped this symbiosis. In the present study, we showed in experiments with gnotobiotic mice that the evolution of Lactobacillus reuteri with rodents resulted in the emergence of host specialization. To identify genomic events marking adaptations to the murine host, we compared the genome of the rodent isolate L. reuteri 100-23 with that of the human isolate L. reuteri F275, and we identified hundreds of genes that were specific to each strain. In order to differentiate true host-specific genome content from strain-level differences, comparative genome hybridizations were performed to query 57 L. reuteri strains originating from six different vertebrate hosts in combination with genome sequence comparisons of nine strains encompassing five phylogenetic lineages of the species. This approach revealed that rodent strains, although showing a high degree of genomic plasticity, possessed a specific genome inventory that was rare or absent in strains from other vertebrate hosts. The distinct genome content of L. reuteri lineages reflected the niche characteristics in the gastrointestinal tracts of their respective hosts, and inactivation of seven out of eight representative rodent-specific genes in L. reuteri 100-23 resulted in impaired ecological performance in the gut of mice. The comparative genomic analyses suggested fundamentally different trends of genome evolution in rodent and human L. reuteri populations, with the former possessing a large and adaptable pan-genome while the latter being subjected to a process of reductive evolution. In conclusion, this study provided experimental evidence and a molecular basis for the evolution of host specificity in a vertebrate gut symbiont, and it identified genomic events that have shaped this process

NACA Research Memorandums

Report presenting testing of free-falling recoverable-model tests at transonic speeds on a model with an aspect-ratio-4 triangular wing and a 45 degree sweptback tail in the extended wing-chord plane. Results regarding the lift, drag, stability, tail effectiveness, and buffet boundary are provided

NACA Technical Notes

"Measurements of propeller efficiency loss due to ice formation are supplemented by an analysis to establish the magnitude of efficiency losses to be anticipated during flight in icing conditions. The measurements were made during flight in natural icing conditions; whereas the analysis consisted of an investigation of changes in blade-section aerodynamic characteristics caused by ice formation and the resulting propeller efficiency changes. Agreement in the order of magnitude of efficiency losses to be expected is obtained between measured and analytical results" (p. 1)

NACA Research Memorandums

"The drag and pressure recovery of a scoop-inlet model have been investigated at transonic speeds by the free-fall testing technique over a Mach number range from about 0.8 to 1.12. Tests were conducted at zero angle of attack, using both rounded and sharp lips at mass-flow ratios from about 0.6 to 0.9. The results indicate that the Mach number of drag divergence of the scoop-inlet model was about the same as that of the basic model without inlets which was tested previously" (p. 1)

Magic Angle Spinning NMR Investigation of Influenza A M2(18-60): Support for an Allosteric Mechanism of Inhibition

The tetrameric M2 proton channel from influenza A virus conducts protons at low pH and is inhibited by aminoadamantyl drugs such as amantadine and rimantadine (Rmt). We report magic angle spinning NMR spectra of POPC and DPhPC membrane-embedded M2[subscript 18−60], both apo and in the presence of Rmt. Similar line widths in the spectra of apo and bound M2 indicate that Rmt does not have a significant impact on the dynamics or conformational heterogeneity of this construct. Substantial chemical shift changes for many residues in the transmembrane region support an allosteric mechanism of inhibition. An Rmt titration supports a binding stoichiometry of >1 Rmt molecule per channel and shows that nonspecific binding or changes in membrane composition are unlikely sources of the chemical shift changes. In addition, doubling of spectral lines in all of the observed samples provides evidence that the channel assembles with twofold symmetry.National Institutes of Health (U.S.) (EB001960)National Institutes of Health (U.S.) (EB002026)National Institutes of Health (U.S.) (Al067438)National Science Foundation (U.S.). Graduate Research Fellowship Progra