BackgroundAlthough the importance of the human oral microbiome for health and disease is increasingly recognized, variation in the composition of the oral microbiome across different climates and geographic regions is largely unexplored.ResultsHere we analyze the saliva microbiome from native Alaskans (76 individuals from 4 populations), Germans (10 individuals from 1 population), and Africans (66 individuals from 3 populations) based on next-generation sequencing of partial 16S rRNA gene sequences. After quality filtering, a total of 67,916 analyzed sequences resulted in 5,592 OTUs (defined at ≥97% identity) and 123 genera. The three human groups differed significantly by the degree of diversity between and within individuals (e.g. beta diversity: Africans > Alaskans > Germans; alpha diversity: Germans > Alaskans > Africans). UniFrac, network, ANOSIM, and correlation analyses all indicated more similarities in the saliva microbiome of native Alaskans and Germans than between either group and Africans. The native Alaskans and Germans also had the highest number of shared bacterial interactions. At the level of shared OTUs, only limited support for a core microbiome shared across all three continental regions was provided, although partial correlation analysis did highlight interactions involving several pairs of genera as conserved across all human groups. Subsampling strategies for compensating for the unequal number of individuals per group or unequal sequence reads confirmed the above observations.ConclusionOverall, this study illustrates the distinctiveness of the saliva microbiome of human groups living under very different climatic conditions.Electronic supplementary materialThe online version of this article (doi:10.1186/s12866-014-0316-1) contains supplementary material, which is available to authorized users.

We have taken the approach of introducing the muscle-specific myosin light chain (MLC)-GLUT4 transgene into the GLUT4-null background to assess the relative role of muscle and adipose tissue GLUT4 in the etiology of the GLUT4-null phenotype. The resulting MLC-GLUT4-null mice express GLUT4 predominantly in the fast-twitch extensor digitorum longus (EDL) muscle. GLUT4 is nearly absent in female white adipose tissue (WAT) and slowtwitch soleus muscle of both sexes of MLC-GLUT4-null mice. GLUT4 content in male MLC-GLUT4-null WAT is 20% of that in control mice. In transgenically complemented EDL muscle, 2-deoxyglucose (2-DOG) uptake was restored to normal (male) or above normal (female) levels. In contrast, 2-DOG uptake in slow-twitch soleus muscle of MLC-GLUT4-null mice was not normalized. With the normalization of glucose uptake in fast-twitch skeletal muscle, whole body insulin action was restored in MLC-GLUT4-null mice, as shown by the results of the insulin tolerance test. These results demonstrate that skeletal muscle GLUT4 is a major regulator of skeletal muscle and whole body glucose metabolism. Despite normal skeletal muscle glucose uptake and insulin action, the MLC-GLUT4-null mice exhibited decreased adipose tissue deposits, adipocyte size, and fed plasma FFA levels that are characteristic of GLUT4-null mice. Together these results indicate that the defects in skeletal muscle and whole body glucose metabolism and adipose tissue in GLUT4-null mice arise independently. ( J. Clin. Invest. 1997. 100:671-677.) Key words: GLUT4 • transgenic mice • knockout mice • glucose metabolism • skeletal muscle

Salt-induced fluxes of H+ , Na + , K + , and Ca 2+ were investigated in ectomycorrhizal (EM) associations formed by Paxillus involutus (strains MAJ and NAU) with the salt-sensitive poplar hybrid Populus 3 canescens. A scanning ion-selective electrode technique was used to measure flux profiles in non-EM roots and axenically grown EM cultures of the two P. involutus isolates to identify whether the major alterations detected in EM roots were promoted by the fungal partner. EM plants exhibited a more pronounced ability to maintain K + /Na + homeostasis under salt stress. The influx of Na + was reduced after short-term (50 mM NaCl, 24 h) and long-term (50 mM NaCl, 7 d) exposure to salt stress in mycorrhizal roots, especially in NAU associations. Flux data for P. involutus and susceptibility to Na + -transport inhibitors indicated that fungal colonization contributed to active Na + extrusion and H + uptake in the salinized roots of P. 3 canescens. Moreover, EM plants retained the ability to reduce the salt-induced K + efflux, especially under long-term salinity. Our study suggests that P. involutus assists in maintaining K + homeostasis by delivering this nutrient to host plants and slowing the loss of K + under salt stress. EM P. 3 canescens plants exhibited an enhanced Ca 2+ uptake ability, whereas short-term and long-term treatments caused a marked Ca 2+ efflux from mycorrhizal roots, especially from NAU-colonized roots. We suggest that the release of additional Ca 2+ mediated K + /Na + homeostasis in EM plants under salt stress.