Surveying of acid-tolerant thermophilic lignocellulolytic fungi in Vietnam reveals surprisingly high genetic diversity

Abstract

Thermophilic fungi can represent a rich source of industrially relevant enzymes. Here, 105 fungal strains capable of growing at 50 °C and pH 2.0 were isolated from compost and decaying plant matter. Maximum growth temperatures of the strains were in the range 50 °C to 60 °C. Sequencing of the internal transcribed spacer (ITS) regions indicated that 78 fungi belonged to 12 species of Ascomycota and 3 species of Zygomycota, while no fungus of Basidiomycota was detected. The remaining 27 strains could not be reliably assigned to any known species. Phylogenetically, they belonged to the genus Thielavia , but they represented 23 highly divergent genetic groups different from each other and from the closest known species by 12 to 152 nucleotides in the ITS region. Fungal secretomes of all 105 strains produced during growth on untreated rice straw were studied for lignocellulolytic activity at different pH and temperatures. The endoglucanase and xylanase activities differed substantially between the different species and strains, but in general, the enzymes produced by the novel Thielavia spp. strains exhibited both higher thermal stability and tolerance to acidic conditions. The study highlights the vast potential of an untapped diversity of thermophilic fungi in the tropics.

Genomic and transcriptomic analysis of the thermophilic lignocellulose-degrading fungus Thielavia terrestris LPH172

“…Poor growth on Avicel could result from lack of cellulase induction or the elevated crystallinity of Avicel. Growth discrepancies between the two T. terrestris strains LPH172 and CBS 117535 corroborate previously reported differences in biomass degradation and enzyme production between strains of the same species (16). Recently, de Vries and Mäkelä reported that related fungi with similar genomic content produced highly diverse sets of enzymes, even when grown on the same plant biomass substrates.…”

“…Isolation and maintenance of fungi Samples containing decaying plant residues (compost, grasses, rice straw, mushroom ground, wood, and soil) were collected from different provinces in Northern Vietnam during 2012-2016. Fungal strains were isolated as described by Thanh et al (16) by incubation at 50 °C and under acidic conditions (pH 2.0) on medium containing untreated rice straw as the sole carbon source. After 7-10 days of incubation, fungal colonies were transferred to potato dextrose agar (PDA) plates and puri ed by hyphal tip culture at 50 °C.…”

“…We previously isolated T. terrestris strain LPH172 from compost in Northern Vietnam and showed that it could be exploited as an industrially relevant enzyme producer (16). To con rm the identity of the fungus, here, we used two common fungal household genes (37) encoding transcription elongation factor 1-α and β-tubulin.…”

“…Thielavia terrestris (syn Thermothielavioides terrestris (11)) is a well-known lamentous fungus identi ed in 1983 as a potential source of thermostable industrial enzymes based on successful (hemi)cellulase assays (12,13). The species is a thermophilic saprobic Ascomycete isolated mainly from soil and compost in Asia (14)(15)(16) and from a cave cricket species in North America (17). As described by Merino and Cherry (18), T. terrestris played a pivotal role in the discovery of lytic polysaccharide monooxygenases (LPMOs).…”

“…In recent years, it has become clear that genetic or gene expression differences between fungal strains of the same species are not uncommon (16,(33)(34)(35)(36). Here, we set out to sequence and analyse the genome and transcriptome of the newly isolated T. terrestris strain LPH172, which is characterised by superior enzymatic activity, thermostability, and pH stability (16). Our current study aimed to elucidate the fungus' lignocellulose degrading machinery in detail and identify novel carbohydrate-active enzymes (CAZymes).…”