Prodigiosin production by Serratia marcescens

Sma 274 was cultured on PG agar and incubated at 28°C for 16 hours. A single bacterial colony was picked and inoculated into 10 mL PGB, followed by incubation at 28°C for 16 hours at 250 rpm in the Innova^TM 4200 Incubator Shaker (New Brunswick Scientific, USA). The optical reading of the culture was then normalised to 0.4 and the normalised bacterial culture was diluted 100× with PG broth and incubated at 28°C for 96 hours. After the 96-hour incubation period, 1 mL of the S. marcescens culture was used to estimate prodigiosin production using the formula below [27]:

Prodigiosin in bacterial culture is detected by observing a single peak at 499 nm (OD₄₉₉) [27]. The value (1.381 × OD₆₂₀) represents the number of bacterial cells so that OD₄₉₉-(1.381× OD₆₂₀) reflects the absorption of prodigiosin. The absorbance value of prodigiosin is then divided by the bacterial cell absorbance value (OD₆₂₀) to express prodigiosin units on a per cell basis and a factor of 1000 is included in the formula to avoid working with small numbers (<1).