I grew two different soil isolates (later identified to be Pseudomonas fluorescens and Janthinobacterium sp.) on LB, TSA and R2A agars.
P. fluorescens grew as a mucoid phenotype only on the LB agar, and Janthinobacterium sp. only produced its pigment, violacein, on the TSA agars.
Both isolates were transferred from a 24-hour nutrient broth culture, and all plates were grown at the same time, at the temperature, etc.
I am trying to speculate why these phenotypes have been observed in only these agar types, and not in the others, but I am struggling to find any real difference between the agars.
Any thoughts would be greatly appreciated!
Dear Grace, the ingredients of the media affect the growth of different type of bacteria. Especially heavy metal ions or minerals stimulate pigmentation in some bacteria. Also the presence of sugars in media, for example sucrose, stimulate extracellular polysaccharides (slime) production of bacteria. For this reason, we prefer selective media to select desired bacteria or general purpose media, (Blood agar, TSA, Nutrient agar etc.) to grow pure bacterial cultures for other tests, antibiotic susceptibility, biofilm assays, etc.
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