Seven microbes and their real-life counterparts
The original Color Lines had seven balls. Here, seven microbes — and each one is based on a real bacterium with its own pigment. All of them genuinely exist and produce these colors on Petri dishes.
Red — Serratia marcescens
A soil-and-tap-water artist. Produces the bright red pigment prodigiosin. In medieval times, its colonies on bread were taken for the «miraculous bleeding» of communion bread. The most photogenic microbe in the dish.
Orange / grey — Rhodococcus and Streptomyces griseus
Orange comes from soil Rhodococcus carrying carotenoid pigments — the same kind that color carrots; they love breaking down oil and plastics. The grey variant is the actinomycete Streptomyces griseus (griseus literally means «grey»): its grey mycelium gave the world the antibiotic streptomycin.
Yellow — Micrococcus luteus
A harmless skin-and-dust dweller. Synthesizes yellow sarcinaxanthin. Colonies look like little drops of lemon paint on agar.
Green — Pseudomonas (pyoverdine)
Pseudomonas produces fluorescent pyoverdine — it glows green under UV. The most luminescent microbe in the lab.
Blue — Pseudomonas (pyocyanin)
The same pseudomonas, but in a different metabolic mode: produces pyocyanin, a deep-blue phenazine pigment. An ink-sapphire stain on the Petri dish.
Purple — Chromobacterium violaceum
A tropical bacterium from soils and fresh waters. Its pigment violacein gives a saturated purple-violet color, and is actively studied as a potential anticancer agent.
Brown — Azotobacter chroococcum
A soil nitrogen-fixer: it pulls nitrogen straight from the air and feeds it to plants. Aging colonies secrete a brown melanin pigment — hence the species name chroococcum, «the one that gives color».