When the final PDF of this article was initially published Figures 2 and 4 were incorrect owing to operator error. We have since updated the article with the correct figures. BioMed Central would like to apologise to the authors and readers for any confusion this may have caused.
Competing interests
Shane Canning is a full-time employee of BioMed Central.
Incorrect figures
9 March 2012
When the final PDF of this article was initially published Figures 2 and 4 were incorrect owing to operator error. We have since updated the article with the correct figures. BioMed Central would like to apologise to the authors and readers for any confusion this may have caused.
Competing interests
Shane Canning is a full-time employee of BioMed Central.