Transcriptome analysis of Aspergillus niger grown on sugarcane bagasse

Abstract

BackgroundConsidering that the costs of cellulases and hemicellulases contribute substantially to the price of bioethanol, new studies aimed at understanding and improving cellulase efficiency and productivity are of paramount importance. Aspergillus niger has been shown to produce a wide spectrum of polysaccharide hydrolytic enzymes. To understand how to improve enzymatic cocktails that can hydrolyze pretreated sugarcane bagasse, we used a genomics approach to investigate which genes and pathways are transcriptionally modulated during growth of A. niger on steam-exploded sugarcane bagasse (SEB).ResultsHerein we report the main cellulase- and hemicellulase-encoding genes with increased expression during growth on SEB. We also sought to determine whether the mRNA accumulation of several SEB-induced genes encoding putative transporters is induced by xylose and dependent on glucose. We identified 18 (58% of A. niger predicted cellulases) and 21 (58% of A. niger predicted hemicellulases) cellulase- and hemicellulase-encoding genes, respectively, that were highly expressed during growth on SEB.ConclusionsDegradation of sugarcane bagasse requires production of many different enzymes which are regulated by the type and complexity of the available substrate. Our presently reported work opens new possibilities for understanding sugarcane biomass saccharification by A. niger hydrolases and for the construction of more efficient enzymatic cocktails for second-generation bioethanol.

Transcriptional Regulation and Responses in Filamentous Fungi Exposed to Lignocellulose

“…HSIPs include proteins such as hydrophobins and other proteins with similar functional properties. Genes that encoded HSIPs, were induced in A. niger in response to wheat straw [31], willow [68] and sugar cane bagasse [69] and in T. reesei in response to wheat straw [135]. The induction of HSIPs suggests a possible role for HSIPs in improving the efficiency of saccharification of lignocellulose.…”

“…The responses to two polysaccharides which are components of lignocellulose (oat spelt xylan and arabinan) were studied by Andersen et al [70] and compared to cultures where monomers (xylose and arabinose) were the carbon source. There were many similarities in the CAZy transcriptional responses of A. niger to wheat straw (at the later time point), willow and pretreated bagasse [31,68,69]. Most of the genes encoding the CAZymes required to break down cellulose and the hemicellulose backbones and side chains were induced.…”

“…Andersen et al [70] described differences in the response of A. niger to different polysaccharide substrates including CAZyme-encoding genes that were only induced on arabinan [70]. Comparisons between the study with the defined polysaccharides [70] to the lignocellulose studies [31,42,68,69] is complicated because the concentrations of xylose in the xylan cultures at the time of sampling have the potential to have a repressing effect on some CAZymeencoding genes as well as an inducing effect on others. A previous study in A.…”

“…For A. niger, there are studies that examine the transcriptional response to the lignocellulosic substrates wheat straw (at two time points) [31,42], willow [68] and pre-treated sugar cane bagasse [69]. The responses to two polysaccharides which are components of lignocellulose (oat spelt xylan and arabinan) were studied by Andersen et al [70] and compared to cultures where monomers (xylose and arabinose) were the carbon source.…”

Integrated Approaches for Assessment of Cellular Performance in Industrially Relevant Filamentous Fungi

“…Transcriptomics also has an important role to play in the identification of genes required for efficient catabolism of carbon sources present in complex and waste substrates. 68,[71][72][73][74] Due to the abundance of xylose in hemicellulose, the regulatory mechanisms involved in using this carbon source as opposed to glucose have been investigated in three different Aspergilli. One study developed and validated a method for transcriptome analysis of Aspergilli, and allowed identification of conserved gene responses to growth on glucose and xylose in A. niger, A. oryzae, and A. nidulans.…”