Biocolorants Production by Pigment-Producing Bacteria Isolated from Soil

Background: The use of synthetic organic colors has been acknowledged for many years as the most reliable and economical method of restoring some of the food’s original shade to the processed products. However, from the health safety point of view, they are not accepted by consumers because they produce skin allergies, less stable and also produce highly toxic wastes that pose a threat to the environment.

The Aim of the Study: The aim was to isolate and identify pigment-producing bacteria from soil and to study various growth parameters for their pigment production.

Materials and Methods: Soil samples were collected from different site within Sokoto State metropolis and were screened on nutrient agar for isolation of pigment-production bacteria. The isolated pigment-producing bacteria were subjected morphological, biochemical and molecular characterization. The phylogenetic analyses of bacterial isolates were carried out using Molecular Evolutionary Genetics Analysis (MEGA 6 software). Ethanol, methanol and chloroform were used for pigments extraction and the extracted pigments were characterized using Ultraviolet-Visible spectroscopy, Fourier Transformed Infrared (FTIR) spectroscopy and thin-layer chromatography (TLC). The effects of growth medium, pH, temperature, incubation time, shaking and static conditions on pigments production was determined. The stability of the pigments was tested toward pH and temperature.

Results: Three (3) isolates that showed purple, orange and blue-green pigment were selected for pigment productions. The isolates were identified as Chromobacterium violaceum, Pseudomonas aeruginosa and Salinococcus roseus. The optimization studies revealed that the Chromobacterium violaceum produced highest purple pigment in nutrient broth at pH 8 for 96 hours of incubation at 35°C under shaking condition while Pseudomonas aeruginosa produced green pigment in nutrient broth at pH 7, 72 hours of incubation at 37°C under shaking condition and Salinococcus roseus produced highest orange pigment on nutrient broth at pH 7, after 96 hours of incubation at 40°C under shaking condition. The characteristics of the pigments corresponded to that violacein, pyocyanin and zeaxanthin based on their FTIR, UV-visible spectroscopy and TLC results. It was found that all the pigments showed good stability at the temperatures of 200°C and fairly stable at lower pH (2).

Conclusion: It therefore concluded that the soil could be the source for isolating pigment-producing bacteria that would offer various industrial applications such textile industries.