Hi,

though I haven't used S. aureus for protein expression, there is something similar in E. coli expression, which may play a role here. What promoter do you use to drive expression, by chance the T7? For E. coli, there are several strains (e.g. BL21 DE3) expressing T7 RNA polymerase, which is required for expression from a T7 promoter, other lines lacking those factors will not give any expression. Do you use the same plasmid / promoter in the working GFP-control construct?

What I would suspect is that your Newman strain lacks a factor required for expression (transcription, translation or folding) of the protein. Does the same DNA-prep (= same clone) work for transfection of the other strain? If not, I guess you have excluded other possibilities, such as mutations?

There are a lot reasons for failed expression, including codon usage, cell toxicity of expressed protein, stability, degradation. You need to optimize each of them. In many cases, it just doesn't work. You need to change expression system if unlucky.

Cydi from EZBiolab

Thank you Mr. Heinrich for your answer. I know from a publication that the mcherry is under a phage repressor promoter that is suppose to drive mcherry expression constitutively. At the moment I am waiting to receive specific information about the plasmid itself and no, I have not tried transfering the plasmid to other strains. However I found several colonies yesterday that faintly express mcherry (at least that is what I think).