Abstract
The thermophilic fungus Humicola insolens produces cellulolytic enzymes that are of great scientific and commercial interest; however, few reports have focused on its cellulase expression regulation mechanism. In this study, we constructed a creA gene (carbon catabolite repressor gene) disruption mutant strain of H. insolens that exhibited a reduced radial growth rate and stouter hyphae compared to the wild-type (WT) strain. The creA disruption mutant also expressed elevated pNPCase (cellobiohydrolase activities), pNPGase (β-glucosidase activities), and xylanase levels in non-inducing fermentation with glucose. Unlike other fungi, the H. insolens creA disruption mutant displayed lower FPase (filter paper activity), CMCase (carboxymethyl cellulose activity), pNPCase, and pNPGase activity than observed in the WT strain when fermentation was induced using Avicel, whereas its xylanase activity was higher than that of the parental strain. These results indicate that CreA acts as a crucial regulator of hyphal growth and is part of a unique cellulase expression regulation mechanism in H. insolens. These findings provide a new perspective to improve the understanding of carbon catabolite repression regulation mechanisms in cellulase expression, and enrich the knowledge of metabolism diversity and molecular regulation of carbon metabolism in thermophilic fungi.
Highlights
The thermophilic fungus Humicola insolens produces an array of enzymes to degrade cellulose and hemicellulose [1,2,3,4,5]
A 1260-bp, full-length creA gene was isolated from H. insolens Y1; it encoded a predicted polypeptide of 419 aammiino aacciiddss iinn lleennggtthh
After six days of fermentation, the maximum Filter paper cellulase (FPase) activity of the creA disruption mutant was observed at 7.89 U/mL, representing 80.43% of the 9.81 U/mL shown by the IWnt.TJ
Summary
The thermophilic fungus Humicola insolens produces an array of enzymes to degrade cellulose and hemicellulose [1,2,3,4,5]. H. insolens exhibits a higher optimal growth temperature (45 ◦C), faster growth rate, and stronger secretion capacity of cellulases [6]. Cellulases produced by H. insolens are active under high temperatures and neutral conditions, and exhibit good thermostability and a wide pH adaptation range, resulting in great application potential in biomass degradation and in the textile, brewing, and feed industries [2,6,7,8]. H. insolens can produce large amounts of foreign proteins. H. insolens is expected to become an excellent cellulase industrial production strain and protein expression system. IInn tthhiiss ssttuuddyy,, ttoo eexxpplloorree tthhee rreegguullaattiioonn bbyy ccrreeAA ggeennee dduurriinngg HH.. TThhiiss iiss tthhee ffiirrsstt rreeppoorrtt ooff ggeennee kknnoocckkoouutt iinn HH.. WWee aallssoo eexxpplloorreedd ccrreeAA ggeennee ffuunnccttiioonn iinn HH.. WWee aallssoo eexxpplloorreedd ccrreeAA ggeennee ffuunnccttiioonn iinn HH.. iinnssoolleennss tthhrroouugghh aann iinntteennssiivvee aannaalylysissisofodfiffdeirffeenrceensciens pihnenpohteynpoetsy, pheysp,hhalymphoarlphmoolorgpyh,oalnodgyc,ellaunldaseceplrloudlauscetiopnrobdeutwcteioenn tbheetwweieldn-ttyhpeew(iWldT-t)ysptrea(iWn,Tth) estcrraeiAn,gtehneecdreiAsrugpentieondimsruutpatniot,nanmductarenAt, caonmdpclreemAecnotmsptrlaeimnse.nFtisntdrainingss. fFrionmdinthgiss sfrtoumdy tehnisricshtuoduyr uennrdicehrstoaunrdiunngdoefrsthtaenmdionlgecouflarthme emchoalnecisumlasr omf eecffihcaineinstmlsignoof ceeflfliuclioesnet dliegcnoomceplolusliotisoen dbeycHom. inpsooslietnios,nanbdy cHon. sitnitsuolteenas,vaanludabcloenfsotuitnudteatiaonvafoluraitbslefufrothuenrdgaetnioenticfoimr pitrsovfuemrthenert tgoenenethicanimcepcreolvluelmaseenpt rtoodeunchtaionnc.e cellulase production
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