Why do microbes produce pigments like pyocyanin rubarin etc?

Answer 1

The color of the compounds the bacteria produce are usually not relevant to their role. Pyocyanin, for example, helps P. aeurginosa acquire iron, inhibit fungal growth, and slow the metabolism in nearby cells by lowering intracellular concentrations of cAMP. It also is a reactive oxygen species, and has been shown to kill C. elegans.

Answer 2

Microbes produce pigments like pyocyanin and rubarin as a defense mechanism against other microbes, as a way to compete for resources and space. These pigments can also serve as signaling molecules in microbial communities to regulate various processes like biofilm formation and virulence.