Abstract
In both natural and man-made environments, microorganisms live in mixed populations, while in laboratory conditions monocultures are mainly used. Microbial interactions are often described as antagonistic, but can also be neutral or cooperative, and are generally associated with a metabolic change of each partner and cause a change in the pattern of produced bioactive molecules. A. niger and A. oryzae are two filamentous fungi widely used in industry to produce various enzymes (e.g. pectinases, amylases) and metabolites (e.g. citric acid). The co-cultivation of these two fungi in wheat bran showed an equal distribution of the two strains forming mixed colonies with a broad range of carbohydrate active enzymes produced. This stable mixed microbial system seems suitable for subsequent commercial processes such as enzyme production. XlnR knock-out strains for both aspergilli were used to study the influence of plant cell wall degrading enzyme production on the fitness of the mixed culture. Microscopic observation correlated with quantitative PCR and proteomic data suggest that the XlnR Knock-out strain benefit from the release of sugars by the wild type strain to support its growth.
Highlights
IntroductionAspergillus represents a large genus. Several species have a long history as cell factories for enzyme production with applications in bioethanol, pulp and paper, textile and food industries (Meyer, 2008)
Among filamentous fungi, Aspergillus represents a large genus
XlnR knock-out strains for both aspergilli were used to study the influence of plant cell wall degrading enzyme production on the fitness of the mixed culture
Summary
Aspergillus represents a large genus. Several species have a long history as cell factories for enzyme production with applications in bioethanol, pulp and paper, textile and food industries (Meyer, 2008). Cellulase activity was increased by using mixed cultures of A. niger and Trichoderma reesei on sugar cane bagasse and cellulose enriched medium (Gutierrez-Correa et al, 1999), (Ahamed and Vermette, 2008). The interaction between these two fungi was recently described as competitive (Daly et al, 2017) and strongly dependent on the conditions of cultivation (Kolasa et al, 2014). Knockout mutants for the (hemi-)cellulolytic regulator XlnR are available, allowing a detailed study of the mixed culture towards plant polysaccharides degradation Both aspergilli are ascomycetes with a growth rate in the same range on various substrates. A byproduct of the flour milling industry because of its composition in polysaccharides (i.e. cellulose, hemicellulose) and aromatics (e.g. ferulic acids) (Laddomada et al, 2015) which makes it an excellent substrate to induce the production of plant biomass degrading enzymes
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