design: Each individual collected a fecal sample from which the total microbial DNA was extracted using the QIAamp DNA Stool Mini Kit (Qiagen, Hilden, Germany) following the manufacturers instructions, with a modication consisting of a bead-beating step with the lysis buffer (20 sec at 15 Hz). A fragment of the gene DNA K chaperone heat protein 70 (dnaK) was amplified with primers designed by us (F_Ru_45_65: YGTNGCNGTNATGGARGGCGG; R_Ru_154_174: NGCCTGNCKYTTTGCVACCTG), and sequenced with Illumina MiSeq cycle flow cell, using a 2x150bp PE sequencing strategy.