Abstract
BackgroundThe filamentous fungus Penicillium oxalicum is a potential alternative to Trichoderma reesei for industrial production of a complete cellulolytic enzyme system for a bio-refinery. Comparative omics approaches can support rational genetic engineering and/or breeding of filamentous fungi with improved cellulase production capacity. In this study, comparative genomic, transcriptomic and secretomic profiling of P. oxalicum HP7-1 and its cellulase and xylanase hyper-producing mutant EU2106 were employed to screen for novel regulators of cellulase and xylanase gene expression.ResultsThe 30.62 Mb P. oxalicum HP7-1 genome was sequenced, and 9834 protein-coding genes were annotated. Re-sequencing of the mutant EU2106 genome identified 274 single nucleotide variations and 12 insertion/deletions. Comparative genomic, transcriptomic and secretomic profiling of HP7-1 and EU2106 revealed four candidate regulators of cellulase and xylanase gene expression. Deletion of these candidate genes and measurement of the enzymatic activity of the resultant mutants confirmed the identity of three regulatory genes. POX02484 and POX08522, encoding a putative Zn(II)2Cys6 DNA-binding domain and forkhead protein, respectively, were found to be novel, while PoxClrB is an ortholog of ClrB, a key transcriptional regulator of cellulolytic enzyme gene expression in filamentous fungi. ΔPOX02484 and ΔPOX08522 mutants exhibited significantly reduced β-glucosidase activity, increased carboxymethylcellulose cellulase and xylanase activities, and altered transcription level of cellulase and xylanase genes compared with the parent strain ΔPoxKu70, with Avicel as the sole carbon source.ConclusionsTwo novel genes, POX02484 and POX08522, were found and characterized to regulate the expression of cellulase and xylanase genes in P. oxalicum. These findings are important for engineering filamentous fungi to improve cellulase and xylanase production.Electronic supplementary materialThe online version of this article (doi:10.1186/s13068-016-0616-9) contains supplementary material, which is available to authorized users.
Highlights
The filamentous fungus Penicillium oxalicum is a potential alternative to Trichoderma reesei for industrial production of a complete cellulolytic enzyme system for a bio-refinery
The filamentous fungus Penicillium oxalicum secretes a complete cellulase system with a high level of BGL activity [3, 5], and P. oxalicum might be a potential alternative to T. reesei for bioenergy applications [3], cellulase production must be enhanced if P. oxalicum is to meet the demands of a commercial cellulase source
Sequencing of the P. oxalicum HP7‐1 genome Penicillium oxalicum strain HP7-1 was isolated from a decayed forest soil system in China [17]
Summary
The filamentous fungus Penicillium oxalicum is a potential alternative to Trichoderma reesei for industrial production of a complete cellulolytic enzyme system for a bio-refinery. In the native extracellular enzyme system of this organism, secretion of β-glucosidase (BGL, EC 3.2.1.21) is low [4], and cellulase preparations from derivatives of T. reesei must be supplemented with BGL from other sources to improve the efficiency of cellulose hydrolysis [3]. The filamentous fungus Penicillium oxalicum secretes a complete cellulase system with a high level of BGL activity [3, 5], and P. oxalicum might be a potential alternative to T. reesei for bioenergy applications [3], cellulase production must be enhanced if P. oxalicum is to meet the demands of a commercial cellulase source
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