Bioconversion of potato solid waste into antifungals and biopigments using Streptomyces spp.

Heidi Schalchli,Emilio Hormazábal,María Cristina Diez,Álvaro Astudillo,Gabriela Briceño,Olga Rubilar,Vijai Gupta

doi:10.1371/journal.pone.0252113

Abstract

Potato waste was processed and used as a sole substrate for simultaneously producing antifungals and biopigments using Streptomyces spp. Out of three different Streptomyces isolates, strain SO6 stood out due to its ability to produce antifungals against economically important fungal phytopathogens and intracellular biopigments using potato waste powders without additional nutrients. This strain also showed the potential to secrete a broad range of enzymes for fermentation of eight sugars that could be involved in potato waste bioconversion. The results of the fermentation assay indicated that Streptomyces sp. strain SO6 degrades potato wastes during submerged fermentation, diminishing total dry weight and increasing reducing sugars from 0.3 to 3.6 mg·mL−1 and total proteins from 70.6 to 187.7 μg·mL−1. The results showed that Streptomyces strain SO6 was able to convert the potato waste into 0.96 mg·g−1 of diffusible antifungals and 1.75 mg·g−1 of reddish-purple biopigments. On the contrary, an absence of pigment production was observed during the fermentation of the commercial medium used as reference. According to our results, replacement of commercial culture media with available low-cost agroindustrial wastes for producing bioactive chemicals is a real opportunity to enhance the Streptomyces pigment production and antibiotic sustainability with cost-competitiveness. To our knowledge, this is the first report on the simultaneous production of biopigments and diffusible antifungal antibiotics produced by Streptomyces spp. using potato solid waste as the sole nutrient source.

Highlights

The agri-food sector generates large amounts of wastes that require sustainable eco-friendly alternatives for utilization rather than waste disposal [1]
We aimed to evaluate the use of potato solid waste as a nutrient source for the simultaneous production of antifungal antibiotics and biopigments by Streptomyces spp. under submerged fermentation
Streptomyces pigments were produced after the third day of submerged fermentation in potato waste, when total protein and reducing sugar contents began to increase

Summary

Introduction

The agri-food sector generates large amounts of wastes that require sustainable eco-friendly alternatives for utilization rather than waste disposal [1]. According to the Food and Agriculture Organization (FAO) [2], one-third of food produced for human consumption is lost every year or wasted throughout the supply chain (~1.3 billion tons). Bioconversion of potato waste into microbial bioproducts be used for synthetizing valuable bioactive compounds [3]. These include enzymes, antibiotics, and biopigments that can be produced by submerged and/or solid fermentation of nutrientrich wastes [3,4,5]. Studies on the replacement of traditional culture media with agro-industrial wastes demonstrated increments of up to 50% pigment production by fungi [6]. Most bacterial pigments are still at the research and development stage; it is necessary to intensify the research on bacterial pigment production to make them available on the market [7]

Objectives

Methods

Results

Discussion

Conclusion