Abstract
A high diversity of fungi was discovered on various substrates collected at the marine shallow-water Kueishan Island Hydrothermal Vent Field, Taiwan, using culture and metabarcoding methods but whether these fungi can grow and play an active role in such an extreme environment is unknown. We investigated the combined effects of different salinity, temperature and pH on growth of ten fungi (in the genera Aspergillus, Penicillium, Fodinomyces, Microascus, Trichoderma, Verticillium) isolated from the sediment and the vent crab Xenograpsus testudinatus. The growth responses of the tested fungi could be referred to three groups: (1) wide pH, salinity and temperature ranges, (2) salinity-dependent and temperature-sensitive, and (3) temperature-tolerant. Aspergillus terreus NTOU4989 was the only fungus which showed growth at 45 °C, pH 3 and 30 ‰ salinity, and might be active near the vents. We also carried out a transcriptome analysis to understand the molecular adaptations of A. terreus NTOU4989 under these extreme conditions. Data revealed that stress-related genes were differentially expressed at high temperature (45 °C); for instance, mannitol biosynthetic genes were up-regulated while glutathione S-transferase and amino acid oxidase genes down-regulated in response to high temperature. On the other hand, hydrogen ion transmembrane transport genes and phenylalanine ammonia lyase were up-regulated while pH-response transcription factor was down-regulated at pH 3, a relative acidic environment. However, genes related to salt tolerance, such as glycerol lipid metabolism and mitogen-activated protein kinase, were up-regulated in both conditions, possibly related to maintaining water homeostasis. The results of this study revealed the genetic evidence of adaptation in A. terreus NTOU4989 to changes of environmental conditions.
Highlights
Our understanding on the diversity of microorganisms of marine shallow-water and deep-sea hydrothermal vent ecosystems is improving
The Ascomycota was dominant in sulfide and black smoker samples at a deep-sea hydrothermal vent site located near the Mid-Atlantic Ridge of the South Atlantic Ocean: 129 isolates belonging to the Ascomycota and 32 isolates to the Basidiomycota [3]
Ten fungi isolated from the sediment and vent crab (Xenograpsus testudinatus) samples collected at/near the hydrothermal vent system at Kueishan Island (121 ̊57’6.01" E, 24 ̊50’30.98" N) between 2015 and 2017 on GYPS (0.4% glucose (BioShop, Ontario, Canada), 0.4% yeast extract (Oxoid, Hampshire, England), 0.4% peptone (Oxoid, Hampshire, England), 30 g sea salt, 1 L distilled water) or one-fifth strength of CDS (Czapek-Dox agar prepared with natural seawater, DifcoTM, BD, Sparks, MD, USA) were selected for the growth study [11]
Summary
Our understanding on the diversity of microorganisms of marine shallow-water and deep-sea hydrothermal vent ecosystems is improving. At various deep-sea hydrothermal vent sites in the Pacific and Atlantic Oceans, ninety-seven fungal isolates were cultured from 210 samples of animal, sediment, rock and seawater samples; most isolates belonged to the Ascomycota while only one basidiomycete was isolated (Tilletiopsis sp.) [2]. In addition to the Ascomycota and the Basidiomycota, sequence signatures of the Chytridiomycota were recovered from animal and rock samples of deep-sea hydrothermal vents at the East Pacific Rise and the Mid-Atlantic Ridge using PCR-cloning-sequencing analysis [7]. Burgaud and co-workers investigated growth of yeast isolates cultured from animals collected at a hydrothermal vent site at the Mid-Atlantic Ridge in response to different salinities and temperatures, and found that majority of the isolates grew at low salinity conditions (0–15 g/L salt) and 25 ̊C while two isolates were able to grow at high salinities (30 and 45 g/L salt) and 35 ̊C [6]
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