Abstract
Effective artificial microbial consortia containing microorganisms with desired biological functions have the potential to optimize the lignocellulose-based bioindustry. Thermobifida fusca was a dominant actinobacterium in high-temperature corn stalk composts, but it was unable to grow alone in corn stalk solid medium. Interestingly, T. fusca showed good growth and secreted enzymes when cocultured with Thermomyces lanuginosus. T. lanuginosus grew firstly during the initial stage, whereas T. fusca dominated the system subsequently during cocultivation. The secretome indicated that T. lanuginosus mainly degraded xylan by expressing a GH11 xylanase (g4601.t1, GenBank AAB94633.1; with relative secretion of 4.95 ± 0.65%). T. fusca was 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 of T. fusca; which may be the reason why T. fusca unable to grow alone in corn stalk solid medium. However, T. lanuginosus could utilize the XOS and xylose produced by xylanases secreted by T. fusca. During the synergistic degradation of lignocellulose by T. lanuginosus and T. fusca, xylan was rapidly consumed by T. lanuginosus, the residual cellulose could specifically induced T. fusca to 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. lanuginosus increased the secretion of cellulases from T. fusca by 19–25%. The order of T. lanuginosus and T. fusca was consistent with the multilayered structures of lignocellulose and could be regulated by different concentrations of XOS and xylose. The novel synergism of T. lanuginosus and T. fusca gave a new sight for revealing more synergetic relationships in natural environments and exploring efficient microbial inoculants and enzyme cocktails for lignocellulose degradation.
Highlights
Plant biomass is the major sink for photosynthetically fixed carbon on earth, and efficient lignocellulose degradation has proven to be crucial for the maintenance of the global carbon cycle and bioprocess development (Alessi et al, 2018)
Complementary Lignocellulose-Degrading Capabilities Between T. lanuginosus and T. fusca Revealed by Genome Analysis
When T. fusca was co-cultured with T. lanuginosus, the bands of xylanases and endocellulases secreted by T. fusca were visible in the native zymograms (Supplementary Figure S2)
Summary
Plant biomass is the major sink for photosynthetically fixed carbon on earth, and efficient lignocellulose degradation has proven to be crucial for the maintenance of the global carbon cycle and bioprocess development (Alessi et al, 2018). The multilayered complex structures of plant cell wall formed the lignocellulose recalcitrance to resist the deconstruction of lignocellulose by microorganisms and enzymes (Burton et al, 2010; McCann and Carpita, 2015; Herbaut et al, 2018; Verbanèiè et al, 2018). Many microbes have been proven to be excellent lignocellulose-degrading enzyme producers; for example, Trichoderma reesei and Penicillium oxalicum (Qian et al, 2016; Song et al, 2016). Industrial conditions, such as high temperatures and extreme pHs are usually too hash to microorganisms and enzymes of which the optimum temperatures are mesophilic. Some studies have been conducted to explore thermotolerant and/or alkaline-resistant enzymes with various industrial application potentials, such as xylanases and cellulases (De Marco et al, 2017; Kumar et al, 2018; Zheng et al, 2018)
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