IBS microbiota and uses thereof

1. A method of diagnosing and treating a subject having IBS, comprising:

determining that the subject will respond to rifaximin by

sequencing the V4 hyper-variable region of the 16S rRNA gene of bacteria obtained from a fecal sample of the subject; and

assigning a number of operational taxonomic units (“OTUs”) based on the V4 hyper-variable region of the 16S rRNA gene sequence to one or more taxa selected from Sphingobacteriaceae, Phyllobacteriaceae, Flavobacteriaceae, Sutterellaceae, Thermoanerobacteraceae, and Burkholderialesincertae sedis,

wherein an OTU includes a cluster of sequences that have at least 97% identity; and

wherein the subject will respond to rifaximin treatment if the number of OTUs is selected from the group consisting of the OTU of Sphingobacteriaceae greater than 2.056, the OTU of Phyllobacteriaceae greater than 0.540, and the OTU of Flavobacteriaceae greater than 2.928, the OTU of Sutterellaceae less than 3.96, the OTU of Thermoanaerobacteraceae less than 0.253, the OTU of Burkholderialesincertae sedis less than 0.259, and any combination thereof before the rifaximin treatment; and

administering an effective amount of rifaximin to the subject who will respond to rifaximin treatment.

2. The method of claim 1 , wherein the taxon is Sphingobacteriaceae.

3. The method of claim 1 , wherein said taxon is Phyllobacteriaceae.

4. The method of claim 1 , wherein said taxon is Flavobacteriaceae.