Prodigiosin from an Endofungal Bacterium Serratia marcescens D1 Inhibits Biofilm Formation in Gram-Positive Bacteria

Prodigiosin, a pink-red pigment produced by many soil isolates of Serratia marcescens as well as by some marine bacterial isolates, is well documented for its bioactive properties. Here, we report the production of prodigiosin by an endofungal bacterium Serratia marcescens D1. The growth characteristics and pigment production were optimized for the bacterial isolate in liquid culture. The bacterial isolate was able to grow abundantly up to 35°C, while maximum pigment production was recorded between 25–30°C, and at pH 5. The pink-red pigment was isolated from the bacterial culture and purified using thin-layer chromatography. The identity of prodigiosin was confirmed by liquid chromatography—electrospray ionization—mass spectrometry (LC-ESI-MS). Antibacterial activity of prodigiosin was assessed against gram-positive and gram-negative bacteria. Prodigiosin showed potent antibacterial activity against gram-positive bacteria, while very low antibacterial activity was observed against gram-negative bacteria used in this study. The minimum inhibitory concentrations (MIC) of prodigiosin against Staphylococcus aureus , Bacillus subtilis and B. cereus were recorded as 3, 5, and 4 µg/mL, respectively. The pigment was able to cause damages to the plasma membrane of Bacillus subtilis and inhibited biofilm formation in B. subtilis and B. cereus, suggesting its active role against biofilm-derived antimicrobial resistance.