Abstract
Microorganisms play a vital role in bioethanol production whose usage as fuel energy is increasing worldwide. The filamentous fungus Neurospora crassa synthesize and secrete the major enzymes involved in plant cell wall deconstruction. The production of cellulases and hemicellulases is known to be affected by the environmental pH; however, the regulatory mechanisms of this process are still poorly understood. In this study, we investigated the role of the pH regulator PAC-3 in N. crassa during their growth on sugarcane bagasse at different pH conditions. Our data indicate that secretion of cellulolytic enzymes is reduced in the mutant Δpac-3 at alkaline pH, whereas xylanases are positively regulated by PAC-3 in acidic (pH 5.0), neutral (pH 7.0), and alkaline (pH 10.0) medium. Gene expression profiles, evaluated by real-time qPCR, revealed that genes encoding cellulases and hemicellulases are also subject to PAC-3 control. Moreover, deletion of pac-3 affects the expression of transcription factor-encoding genes. Together, the results suggest that the regulation of holocellulase genes by PAC-3 can occur as directly as in indirect manner. Our study helps improve the understanding of holocellulolytic performance in response to PAC-3 and should thereby contribute to the better use of N. crassa in the biotechnology industry.
Highlights
The filamentous fungus Neurospora crassa is an appealing microorganism for use by the bioethanol industry, because it degrades biomass releasing fermentable sugars [1]
To determine whether PAC-3 affects the secretion of hollocellulolytic enzymes by the fungus, we analyzed the profile of total cellulolytic (FPase), endoglucanase (CMCase), and xylanolytic activities in strains 74A, Δpac-3, and Δmus-52 (Fig 2)
They observed that total cellulolytic activity was higher in the mutant strain ΔTrpac1 at neutral pH, as we showed for N. crassa, suggesting that T. reesei and N. crassa may share a similarity in PAC-3
Summary
The filamentous fungus Neurospora crassa is an appealing microorganism for use by the bioethanol industry, because it degrades biomass releasing fermentable sugars [1]. Many isolates of this species were collected from sugarcane plantations [2,3,4] exhibiting the synthesis and secretion of holocellulolytic enzymes involved in plant cell wall degradation [5].
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