It is very interesting to note that freshwater samples are more

related with terrestrial samples than with marine ones. This indicates that salinity is a very important selective factor for the composition of prokaryotic communities, and more relevant than the apparently loose distinction between aquatic and terrestrial Compound C nmr media, as was also described by Lozupone and Knight using a strictly phylogenetic approach [20]. Many prokaryotic taxa found in soil samples, may actually thrive in the interstitial water within soil particles [29], which could explain the highest similarity between the taxonomic profiles of freshwater and soil environments. When performing the analysis for environmental subtypes, the trends above are shown again, but new details emerge (Additional file 5, Figure S3). As before, host-associated Selleckchem ARN-509 habitats obviously separate from the

rest, but on this occasion the cluster includes the samples related to food treatments and compost. Thermal environments form the second clear division. The next groups to separate correspond to nutrient-rich soils (forests, grasslands and agricultural soils), and to saline environments. Interestingly, the latter are all aquatic except for saline soils, which cluster with this saline subgroup rather than with other Selleck CRT0066101 soil subtypes, thus illustrating the importance of salinity. The remaining groups are formed by a mixture of artificial, Resveratrol freshwaters and nutrient-poor soils that do not separate clearly. The conspicuous distinction

between rich and poor soil types correlates with the increase of several taxa in rich soils (especially Actinobacteria), and is in accordance with previous studies [30]. To further explore the relationships between environments and taxa, we carried out a Detrended Correspondence Analysis (DCA), a well-known multivariate technique traditionally used in ecology to explore patterns of variation in community data matrices. Figure 4 shows the results for family level. The first two resulting axes allow the discrimination between environments according to their taxonomic profiles. The first axis clearly separates animal tissues from other environments. The second axis discriminates saline and thermal environments from the rest. Freshwaters and soil samples are nearby and they both are close to the origin, thus indicating the absence of very specific taxa in them. This result supports the division in the five main environmental groups found earlier. Figure 4 Bi-plot of environment types and taxonomic families. The axes correspond to the first two components of a detrended correspondence analysis (DCA). Percentages in brackets refer to the proportion of inertia explained by the axes. A measure of the complexity of the composition of the different environments can be obtained by means of the diversity indices calculated from the abundance of taxa in the samples from these environments.