Correction to: Nature Microbiology https://dx.doi.org/10.1038/s41564-017-0030-5 (2017); published online 2 October 2017.

In the version of this Letter originally published, the authors incorrectly stated that primers 28F-519R were reported in ref. 54 to underestimate the abundance of SAR11 in the ocean. This statement has now been amended in all versions of the Letter.