A new endophyte Monascus ruber SRZ112 as an efficient production platform of natural pigments using agro-industrial wastes

Abstract

A number of biopigment applications in various industrial sectors are gaining importance due to the growing consumer interest in their natural origin. Thus, this work was conducted to valorize endophytic fungi as an efficient production platform for natural pigments. A promising strain isolated from leaves of Origanum majorana was identified as Monascus ruber SRZ112 produced several types of pigments. The nature of the pigments, mainly rubropunctamine, monascin, ankaflavin, rubropunctatin, and monascorubrin in the fungal extract was studied by LC/ESI-MS/MS analyses. As a first step towards developing an efficient production of red pigments, the suitability of seven types of agro-industrial waste was evaluated. The highest yield of red pigments was obtained using potato peel moistened with mineral salt broth as a culture medium. To increase yield of red pigments, favourable culture conditions including incubation temperature, incubation period, pH of moistening agent, inoculum concentration, substrate weight and moisture level were evaluated. Additionally, yield of red pigments was intensified after the exposure of M. ruber SRZ112 spores to 1.00 KGy gamma rays. The final yield was improved by a 22.12-fold increase from 23.55 to 3351.87 AU g^-1. The anticancer and antioxidant properties of the pigment's extract from the fungal culture were also studied. The obtained data indicated activity of the extract against human breast cancer cell lines with no significant cytotoxicity against normal cell lines. The extract also showed a free radical scavenging potential. This is the first report, to our knowledge, on the isolation of the endophytic M. ruber SRZ112 strain with the successful production of natural pigments under solid-state fermentation using potato peel as a substrate.

Figure 1

Morphological characteristics of the red pigments-producing fungal strain. Colony growth was observed on Czapek–Yeast autolystae agar. The plate cultures on the left show a front view of the growth (A), and the plate cultures on the right show a reverse view (B) of the growth after incubation for 10 days at 25 °C. Appearance under light microscope (C,D).

Figure 2

Phylogenetic tree of the pigment-producing fungal strain (AUMC14390) and other closely related strains of Monascus, based on the ITS1-5.8S rRNA-ITS2 rDNA sequences.

Figure 3

Effect of different incubation temperatures (A) and effect of different incubation periods (B) on growth (mg g⁻¹) and red pigments production (AU g⁻¹) by Monascus ruber SRZ112 under SSF. Initial pH of the MSB moistening agent was adjusted to 6.0 using 1 N NaOH and HCl. Solid–state grown cultures were carried out on potato peel. All data are shown as the mean ± SD of triplicate measurements from two independent experiments.

Figure 4

Effect of adjusting the pH of the MSB to different values (A) and effect of different inoculum concentrations (B) on growth (mg g⁻¹) and red pigments production (AU g⁻¹) by Monascus ruber SRZ112 under SSF. Initial pH of the MSB moistening agent was adjusted to varying values using 1 N NaOH and HCl. Solid–state grown cultures were carried out on potato peel at 30 °C for 10 days. All data are shown as the mean ± SD of triplicate measurements from two independent experiments.

Figure 5

Effect of different weights of potato peel as substrate (A) and effect of different moisture levels (B) on growth (mg g⁻¹) and red pigments production (AU g⁻¹) by Monascus ruber SRZ112 under SSF. Initial pH of the MSB moistening agent was adjusted to 6.0 using 1 N NaOH and HCl. Solid–state grown cultures were carried out on potato peel at 30 °C for 10 days. All data are shown as the mean ± SD of triplicate measurements from two independent experiments.

Figure 6

LC/ESI–MS/MS chromatograms of pigments extracted from SSF cultures of the gamma irradiated M. ruber SRZ112. Spectrum and structure of monascin (A). Spectrum and structure of rubropunctatin (B). Spectrum and structure of ankaflavin (C). Spectrum and structure of monascorubrin (D). Spectrum and structure of rubropunctamine (E).