Insight into the adaptation mechanisms of high hydrostatic pressure in physiology and metabolism of hadal fungi from the deepest ocean sediment.

High hydrostatic pressure (HHP) influences the life processes of organisms living at depth in the oceans. While filamentous fungi are one of the essential members of deep-sea microorganisms, few works have explored their piezotolerance to HHP. Here, we obtained three homogeneous Aspergillus sydowii from terrestrial, shallow, and hadal areas, respectively, to compare their pressure resistance. A set of all-around evaluation methods including determination of growth rate, metabolic activity, and microscopic staining observation was established and indicated that A. sydowii DM1 from the hadal area displayed significant piezotolerance. Global analysis of transcriptome data under elevated HHP revealed that A. sydowii DM1 proactively modulated cell membrane permeability, hyphae morphology, and septal quantities for seeking a better livelihood under mild pressure. Besides, differentially expressed genes were mainly enriched in the biosynthesis of amino acids, carbohydrate metabolism, cell process, etc., implying how the filamentous fungi respond to elevated pressure at the molecular level. We speculated that A. sydowii DM1 could acclimatize itself to HHP by adopting several strategies, including environmental response pathway HOG-MAPK, stress proteins, and cellular metabolisms.IMPORTANCEFungi play an ecological and biological function in marine environments, while the physiology of filamentous fungi under high hydrostatic pressure (HHP) is an unknown territory due to current technologies. As filamentous fungi are found in various niches, Aspergillus sp. from deep-sea inspire us to the physiological trait of eukaryotes under HHP, which can be considered as a prospective research model. Here, the evaluation methods we constructed would be universal for most filamentous fungi to assess their pressure resistance, and we found that Aspergillus sydowii DM1 from the hadal area owned better piezotolerance and the active metabolisms under HHP indicated the existence of undiscovered metabolic strategies for hadal fungi. Since pressure-related research of marine fungi has been unexpectedly neglected, our study provided an enlightening strategy for them under HHP; we believed that understanding their adaptation and ecological function in original niches will be accelerated in the perceivable future.

High hydrostatic pressure harnesses the biosynthesis of secondary metabolites via the regulation of polyketide synthesis genes of hadal sediment-derived fungi.

Deep-sea fungi have evolved extreme environmental adaptation and possess huge biosynthetic potential of bioactive compounds. However, not much is known about the biosynthesis and regulation of secondary metabolites of deep-sea fungi under extreme environments. Here, we presented the isolation of 15 individual fungal strains from the sediments of the Mariana Trench, which were identified by internal transcribed spacer (ITS) sequence analysis as belonging to 8 different fungal species. High hydrostatic pressure (HHP) assays were performed to identify the piezo-tolerance of the hadal fungi. Among these fungi, Aspergillus sydowii SYX6 was selected as the representative due to the excellent tolerance of HHP and biosynthetic potential of antimicrobial compounds. Vegetative growth and sporulation of A. sydowii SYX6 were affected by HHP. Natural product analysis with different pressure conditions was also performed. Based on bioactivity-guided fractionation, diorcinol was purified and characterized as the bioactive compound, showing significant antimicrobial and antitumor activity. The core functional gene associated with the biosynthetic gene cluster (BGC) of diorcinol was identified in A. sydowii SYX6, named as AspksD. The expression of AspksD was apparently regulated by the HHP treatment, correlated with the regulation of diorcinol production. Based on the effect of the HHP tested here, high pressure affected the fungal development and metabolite production, as well as the expression level of biosynthetic genes which revealed the adaptive relationship between the metabolic pathway and the high-pressure environment at the molecular level.

High hydrostatic pressure shapes the development and production of secondary metabolites of Mariana Trench sediment fungi.

The hadal biosphere is one of the least understood ecosystems on our planet. Recent studies have revealed diverse and active communities of prokaryotes in hadal sediment. However, there have been few studies on fungi in hadal sediment. Here we report the first isolation and cultivation of 8 fungi from the Mariana Trench sediment. The individual colonies were isolated and identified as Stemphylium sp., Cladosporium sp., Arthrinium sp., Fusarium sp., Alternaria sp., and Aspergillus sp. High hydrostatic pressure (HHP) test was carried out to identify the piezophily of these hadal fungi. Among them, 7 out of the 8 fungal isolates exhibited the ability of germination after incubation under 40 MPa for 7 days. Vegetative growth of the isolates was also affected by HHP. Characterization of secondary metabolites under different pressure conditions was also performed. The production of secondary metabolites was affected by the HHP treatment, improving the potential of discovering novel natural products from hadal fungi. The antibacterial assay revealed the potential of discovering novel natural products. Our results suggest that fungal growth pressure plays an important role in the development and production of secondary metabolites of these hadal fungi under the extreme environment in the Mariana Trench.