The authors of Rennie et al. (2017) paper think microbes are not so different from robots designed artificially with the capability of responding to the surrounding environment.
The authors first argue that the slime mold has a sense of intelligence by advancing towards in the direction with more nutrients by pumping cytoplasm in that direction. Additionally, slime mold has the ability of leaving chemical trails which reminds it places not worth visiting.
Further, the authors discuss the intelligence of bacteria, especially biofilms. First, they argue that biofilms have sophisticated structures which allow them to absorb nutrients nearby as much as possible. Moreover, the cells in biofilms have different functions depending on the location of the cells in the biofilms. Similar to slime mold, biofilms have the capability of moving towards locations with more nutrients by secreting materials which help them move more energetically and more rapidly.
Additionally, biofilms have different spiral migration pattern depending on their genes. Biofilms also are intolerant of other strains so they develop boundaries between each other when forming.