Prodigiosin isolated from Serratia�marcescens in the Periplaneta�americana gut and its apoptosis‑inducing activity in HeLa cells

Serratia marcescens are considered to be abundant and optimal resources for obtaining prodigiosin, which can be isolated from soil, water, plants and air but rarely from insects. In the present study, a strain of Serratia marcescens named WA12‑1‑18 was isolated from the gut of Periplaneta americana, which was capable of producing high levels of pigment reaching 2.77 g/l via solid fermentation and was identified as prodigiosin by ultraviolet, high performance liquid chromatography (LC), Fourier‑transform infrared spectroscopy, LC‑mass spectroscopy and nuclear magnetic resonance. The apoptotic tumor cells treated with prodigiosin were examined by 4',6‑diamidino‑2‑phenylindole (DAPI) staining assays and transmission electron microscopy. Flow cytometry (FCM) was utilized to measure the apoptotic rate with Annexin V staining and the expression levels of proteins involved in apoptosis, including B‑cell lymphoma 2 (Bcl‑2), Bcl‑2‑associated X (Bax) and caspase‑3 were determined by western blot analysis and reverse transcription‑quantitative polymerase chain reaction (RT‑qPCR). The experimental results revealed that prodigiosin could inhibit the proliferation of HeLa cells and the half‑maximal inhibitory concentration values of prodigiosin in HeLa were 2.1, 1.2 and 0.5 µg/ml over 24, 48 and 72 h, respectively. Furthermore, DAPI staining assays and transmission electron microscopy clearly demonstrated that prodigiosin could induce HeLa cell apoptosis. FCM results revealed that the cell apoptotic rates were 19.7±1.4, 23.7±2.4 and 26.2±2.3% following the treatment with 0.5, 1.0 and 2.0 µg/ml prodigiosin for 48 h, respectively. Western blot analysis and RT‑qPCR revealed that prodigiosin could activate apoptosis‑associated molecules including Bcl‑2, Bax and caspase‑3. Therefore, the results of the present study demonstrated that the prodigiosin could induce apoptosis in HeLa cells, which may be associated with the upregulation of Bax and caspase‑3, the concomitant downregulation of Bcl‑2 levels and also triggering the extrinsic apoptotic signaling pathway.