Purple biofilm gives Bacillus subtilis a run for its money

Scott Chimileski

Colonies formed by purple soil isolate on agar medium.

One of the students in the Small World Initiative lab I instruct isolated this very interesting species with an intense purple pigmentation and robust biofilm formation.

We aren’t sure what it is yet, but it shows antimicrobial activity against some other bacterial species and from what research we have done we suspect it may a member of the genus Janthinobacterium.  These organisms produce a purple pigment called violacein.

The media we use contains a chemical to select against fungi, but being astonished by the three dimensional structure of this biofilm we were eager to confirm that it is indeed a bacterium.

Soil isolate 3.2014

Gram stain of purple soil isolate. Conduced by SWI student Rofina Johnkennedy.

We did a Gram stain, which was a bit challenging considering the wax-like texture of this biofilm. After first failing to break apart he biofilm by aggressive vortexting and pippeting in liquid medium, we found that low power sonication was the most effective method for isolating and staining single cells and groups of cells. And, it is a Gram negative rod.


These colonies had a waxy texture with a clear sheen that reflected light.

How millions of individual seemingly identical and simple cells come together to form such complex structure is truly amazing.  This guy would give Bacillus subtilis a run for it’s money.