CAZyome and Sugar Transportome Unveil Singular Aspects of the Lignocellulolytic Enzyme System of Penicillium echinulatum 2HH

Abstract

Background: The production of bioethanol using lignocellulosic feedstocks has proved to be a cutting-edge technology. However, this technology faces limitations such as cost and yield of enzymatic systems, required to degrade efficiently the polysaccharides of plant cell walls. Penicillium echinulatum 2HH is a widely studied ascomycete, known by its efficient cellulolytic cocktails. One strategy to improve the saccharification yields for commercial exploitation is the design of hypersecreting strains. However, molecular knowledge about the lignocellulolytic system of this specific fungus is scarce. Understanding both lignocellulolytic and sugar uptake systems is essential to obtain industrial strains with adequate efficiency for bioethanol production. Results: We report a comprehensive in silico characterization of CAZymes and sugar transporters of P. echinulatum 2HH. The CAZyome reveals an outstanding repertoire of enzymes involved in plant biomass degradation. Among them, we highlight the cellulolytic enzyme system whose genes are predominantly orthologous to P. oxalicum 114-2, demonstrating the high similarity of these phylogenetically related enzyme producers. We also report a LPMO-type enzyme of the AA16 family described for the first time in these fungi. In addition to the well-known high activity of ß-glucosidases, we found that coding genes for the AA16, GH5-4 and GH45 families comprehend the main differences in the cellulolytic complexes of P. echinulatum 2HH and P. oxalicum 114-2, when both are compared to commercial producers. Our phylogenetic analysis of the sugar transportome suggests that P. echinulatum 2HH diversity and specificity of STs include eight major families with specificity to different groups of sugars. Finally, our phylogenetic analyses enabled the identification of several iBGLs and STs potentially involved in the accumulation of intracellular cellodextrins.Conclusions: Overall, both CAZyome and sugar transportome of P. echinulatum revealed new insights into the mechanisms underlying a flexible and highly functional metabolism to degrade plant biomass. Peculiarities found in our study help to highlight the cellulolytic complex of P. echinulatum 2HH, contributing to the commercial ascendance of Penicillium spp. as cellulolytic enzyme producers. Furthermore, the first phylogenetic classification of STs and iBGLs shed new light into the role of these genes regarding the preferred carbon source during fungal growth. Along these lines, these iBGLs and STs comprise valuable gene targets to understand the regulatory mechanisms underlying cellulolytic enzymes and to design hypersecreting strains with adequate efficiency for bioethanol production in large-scale.