Dear Grace Forsythe

Similarly, in the production processes of melanin pigment from Streptomyces strains, sometimes i get a dark black eumelanin; sometimes i get a brownish pyomelanin pigment. I think, you are getting pyocyanin and pyoverdine pigments in your researches. It is possible to obtain different pigments even if all parameters and external factors are the same. Some researchers, whose opinions I asked, stated that this situation may be caused by contamination. But no matter how much we pay attention to aseptic techniques, the same bacteria can produce different pigments under the same conditions. I think this issue is caused by epigenetic factors and maybe it may be necessary to conduct transcriptomic and proteomic researches to clarify this issue.

This situation may even depend on whether the inoculum from the medium is taken from 24-hour or 48-hour cultures.

I do not know about your research topic, but if you are working on a subject other than pigment production, you should not doubt the reliability of your results.

I am working on both bacteria and fungi.

for fungal pigmentation, the colony colors will change depend on the volume medium, dark-light condition, temperature, etc.

But in bacteria I never experienced such things like yours. I think, just my personal opinion, are you sure your bacteria culture not contaminated? please spread on LA medium or extract the DNA from your culture and do PCR with 16S primer pairs and check on gel electrophoresis. Do this step on both your yellow and your bright green colonies. you will find out both are same or different. if both are same then you can conclude its due to your bacteria pigmentation

Hi Grace,

It's quite natural to observe green colour of PA01 culture because of pyocyanin production. Pyocyanin production in PA01 is controlled by quorum sensing mechanism. This is the reason, Why you observed different colour of PA01. Pyocyanin will be produced when the cells attain a particular quorum. When the cell number is less, it will be in yellow. When the cells are more, QS can regulate pyocyanin production and hence green.

1. Try to use known number of cells as inoculum. Thereby you can get reproducible results.

2. If you are worried about possible contamination, use cetrimide agar for discriminating PA from contaminants.

Hope this will help you. Other than that, if you are going for PCR based identification, you have to sequence 16S amplicons. Just checking on agarose gel will not give any conclusive results except PA specific primers.

All the best for your research.