Novel Synergistic Mechanism for Lignocellulose Degradation by a Thermophilic Filamentous Fungus and a Thermophilic Actinobacterium Based on Functional Proteomics

Effective artificial microbial consortia containing microorganisms with desired biological functions have the potential to optimize the lignocellulose-based bioindustry.Thermobifida fuscawas a dominant actinobacterium in high-temperature corn stalk composts, but it was unable to grow alone in corn stalk solid medium. Interestingly,T. fuscashowed good growth and secreted enzymes when cocultured withThermomyces lanuginosus.T. lanuginosusgrew firstly during the initial stage, whereasT. fuscadominated the system subsequently during cocultivation. The secretome indicated thatT. lanuginosusmainly degraded xylan by expressing a GH11 xylanase (g4601.t1, GenBank AAB94633.1; with relative secretion of 4.95 +/- 0.65%).T. fuscawas induced by xylan mainly to secrete a xylanase from GH11 family (W8GGR4, GenBank AHK22788.1; with relative secretion of 8.71 +/- 3.83%) which could rapidly degrade xylan to xylo-oligosaccharide (XOS) and xylose within 2 min, while high concentrations (>0.5%, w/v) of XOS or xylose suppressed the growth ofT. fusca; which may be the reason whyT. fuscaunable to grow alone in corn stalk solid medium. However,T. lanuginosuscould utilize the XOS and xylose produced by xylanases secreted byT. fusca. During the synergistic degradation of lignocellulose byT. lanuginosusandT. fusca, xylan was rapidly consumed byT. lanuginosus, the residual cellulose could specifically inducedT. fuscato express a GH10 xylanase with a CBM2 domain (Q47KR6, GenBank AAZ56956.1; with relative secretion of 5.03 +/- 1.33%) and 6 cellulases (2 exocellulases and 4 endocellulases). Moreover,T. lanuginosusincreased the secretion of cellulases fromT. fuscaby 19-25%. The order ofT. lanuginosusandT. fuscawas consistent with the multilayered structures of lignocellulose and could be regulated by different concentrations of XOS and xylose. The novel synergism ofT. lanuginosusandT. fuscagave a new sight for revealing more synergetic relationships in natural environments and exploring efficient microbial inoculants and enzyme cocktails for lignocellulose degradation.