Fig. 3
![Fig. 3](http://media.springernature.com/full/springer-static/image/art%3A10.1186%2Fs13068-019-1490-z/MediaObjects/13068_2019_1490_Fig3_HTML.png)
Improvement of putrescine tolerance of M. alcaliphilum 20Z by adaptive evolution. Filled circles show the wild-type strain M. alcaliphilum 20Z grown in NMS. The open circles show the evolved strain in NMS, while the filled triangles show the evolved strain exposed to 100Â mM of putrescine dihydrochloride. The open triangles show the evolved strain exposed to 200Â mM of putrescine dihydrochloride, and the filled squares show the evolved strain with 400Â mM of putrescine dihydrochloride