Spore germination of fungi belonging to Aspergillus species under deep-sea conditions

Wind-blown dry fungal spores and mycelial fragments from the nearest landmass or terrestrial run-off may find their way to the deep sea by hitching a ride on other sinking detrital particles. Once in the deep, they are affected by elevated hydrostatic pressure, low temperature and low nutrients. We have examined effects of these on germination of spores from a few deep-sea Aspergillus isolates. Spores from most of the fungi germinated under elevated hydrostatic pressure at 30 °C. The ambient temperature of the deep sea, ∼4–5 °C, was found to inhibit spore germination totally. Sediment extracts prepared in seawater promoted spore germination as did additions of dimethylsulfoxide and sucrose, but only at 30 °C/200 bar pressure and not at 4–5 °C. Heat shock of 15 min at 50 °C helped in breaking the dormancy of the spores and induced germination at 5 °C at 1 bar pressure but not at 200 bar. More than 90% of the spores from several deep-sea Aspergillus isolates and the terrestrial isolate of Aspergillus terreus lost viability within 16–17 days of incubation at 5 °C/1 bar. About 2–3% remained viable for more than 3 months at 5 °C/1 bar. Mycelial fragments showed growth and biomass production under elevated pressure at 5 °C. These results indicate that building biomass under deep-sea conditions from spores is not a viable option for the deep-sea Aspergillus isolates. Mycelial fragments, on the other hand, are more likely to grow.