I have isolated from water some strange-looking colonies on YDC medium. In fact they are dark violet. Do you have any idea about taxonomic position of this bacteria?
These may be marine, violacein-producing strains of Janthinobacterium spp. or Duganella spp.
What morphology does these microbes have under a light microscope?
@Pawel,
Thank you! It looks like Janthinobacterium indeed. One flagella. I have isolated recently pigmented Janthinobacterium spp. from potato tubers, and will compare them.
Alex
I can also suggest that when growing pigmented bacteria (e.g. Janthinobacterium spp.), environmental stress is an important factor "forcing" microorganisms to maintain pigment formation. In too favorable in vitro conditions, these bacteria often lose their ability of pigmentation after passaging. The presence of low concentrations of antibiotics or other stressors in culture media can induce pigmentation in these microbes.
@Pawel, I noticed that the pigmentation was weaker at plates of higher dilution and smaller number of other bacteria - pigment production was a reaction to presence of other species on the same plate.
@Alex, exactly. The production of violacein is quorum sensing-dependent and therefore the presence of high bacterial densities (of the same species or other species) has often a positive effect on the production of violet pigment by these bacteria.
Similar observations were made during my research: (I) on solid plates, on which purple-pigmenting bacteria were sown, violet colonies appeared gradationally (from areas of highest density to lowest), (II) in liquid cultures the formation of intense pigment most often occured inhomogeneously, for example, by 18h the bacterial culture remained slightly violet, after which the intensity of the pigment increased several times within an hour (potential transition to the stationary phase and activation of genes responsible for the violacein production).
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