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Purpose The purpose of this paper was to identify Serratia marcescens to extract and purify prodigiosin pigment to evaluate the antibacterial potential of the pigment. Design/methodology/approach Samples were collected from shrimp aquaculture ponds. Species identification was conducted using morphological, biochemical and molecular tests. Pigment extraction and purification were carried out using column chromatography. The antibacterial effect of crude and purified prodigiosin pigment was evaluated on Escherichia coli, Bacillus subtilis, Pseudomonas aeruginosa and Staphylococcus aureus as biofouling bacteria. In addition, the interaction between prodigiosin and proteins involved in biofilm formation was evaluated using molecular docking. Findings The results of prodigiosin extraction with solvents showed the highest percentage of pigment presence with methanol solvent in the second day of culture. The chemical structure of pure prodigiosin obtained from the column chromatography was confirmed by Fourier-transform infrared spectroscopy. Both crude and purified pigments exhibited antibacterial effects against selected bacterial strains. The antibacterial effect of the purified pigment was higher, and the highest antibacterial effect was observed on B. subtilis. Prodigiosin docking was carried out with all target proteins, and the docked energy in all of them was at an acceptable level. Originality/value Prodigiosin extracted from S. marcescens can be used as a bioactive compound to design and manufacture of anti-biofouling and anti-biofilm formation products to use extensively for industrial applications as a natural color in marine industries, food industry, cosmetics and textile productions.

Bacteria of the genus Raoultella are known to inhabit aquatic environments and can be found in medical samples. The pathogenicity of Raoultella ornithinolytica isolates in human has become increasingly important, and several cases of infections have been reported recently. However, there are no reports of isolation of bacteriophages infecting this bacterium. In this study, two novel phages (ISF3 and ISF6) of a methylotrophic Raoultella strain were isolated from sewage. To characterize the isolated phages, morphological features, protein profiles, restriction digestion patterns, and partial genome sequences were studied. Despite morphological differences, electron microscopy revealed that both phages had an icosahedral capsid connected to a contractile tail, suggesting that ISF3 and ISF6 both belong to the family Myoviridae. Partial nucleotide sequences of the ISF3 genome showed 99% to 100% identity to DNA of Klebsiella pneumonia phages KP15, KP27 and BMBT1; however, the restriction digestion profiles of ISF3 genome digested by EcoRI and EcoRV differed from those of Klebsiella phages KP15 and KP27. A partial sequence alignment showed that ISF6 can be classified as a member of a new viral genus due to its significant differences from other previously identified phages. To the best of our knowledge, this is the first report of the isolation and characterization of the specific Raoultella phages that have potential to be used as new pharmaceuticals against R. ornithinolytica.