From the article:
Controlling for the influence of other factors known to impact mental health, such as diet and sleep, the researchers found that students with recent suicidal thoughts had higher levels of bacteria associated with periodontal disease and other inflammatory health conditions. […] They also found that these students had lower levels of Alloprevotella rava, a bacterium known to produce a compound that promotes brain health.
The bacteria:
One Fusobacteriaceae species, Fusobacterium naviforme, was found higher in individuals with SI. Veillonella atypica was observed in elevated abundances in individuals with SI.