Correction to: The ISME Journal advance online publication, 21 March 2013; doi:10.1038/ismej.2013.37

Since the online publication of this article, the authors have noticed that a supplementary file has not been included with the paper.

The supplementary file (Supplementary file 4) has now been included, and appears alongside the online version of the original article.

The authors would like to apologize for any inconvenience this may have caused.