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.

Bacterial physiological behavior extremely depends on the environmental condition so temperature, pH and growth condition may influence to produce different color. Another important thing is quorum sensing condition, where different strain can exchanges their enzymatic and metabolic components which can trigger up different gene expression. You should consider the cross contamination during experiment as well.