Species Richness and Adaptation of Marine Fungi from Deep-Subseafloor Sediments

Fungi have developed unique adaptation that have allowed them to colonize a range of habitats from terrestrial to marine, as well as occupy a variety of extreme and non-extreme environmental niches. One such environmental niche is deep subseafloor sediment where fungi have been identified at depths from a few centimetres to 1740m below the sea floor (mbsf). At these kinds of depths physical and chemical properties including; low nutrient availability, salinity, hydrostatic and lithostatic pressure, amongst others, set limitations on habitability. Past studies have shown, using molecular methods and cultured isolates, that although fungi are present at great depths below the seafloor, not a lot is known about their role in these ecosystems. This study by Redou et al (2015) set out to determine the distribution of culturable communities along a deep sea sediment core, characterize their ecophysiological profiles and ability to withstand extreme abiotic conditions, and finally to test their potential in the synthesis of bioactive compounds, that could have some potential in biotechnological applications.

A sediment core was drilled 1927.5 mbsf during the Integrated Ocean Drilling Programme (IODP) in the Canterbury Basin near New Zealand. 11 subsamples that ranged from 4 – 1884 mbsf were analysed. They were grown on 5 different media at varying temperatures, pressures and nutrient availability to mimic the in situ conditions. DNA was extracted from the isolates and various methods of PCR amplification carried out for genetic identification and fingerprinting before phylogenetic analyses were carried out using BLAST. Growth rates were measured and the presence of genes involved in the production of secondary metabolites was investigated.  

10 of the 11 samples (91%) yielded culturable fungi. As expected the overall phylogenetic diversity was relatively low when compared to organic rich terrestrial and marine environments. The greatest diversity was found in the upper sediment down to 37 mbsf with 25 species accounting for 92% of the whole diversity within the entire fungal culture. At greater depths (137 – 1844 mbsf) there was only 8 species. The phyla Ascomycota dominated filamentous fungal collection and Basidiomycota dominated the yeast collection which is generally consistent with work done on deep sea sediments from the Central Indian Basin. Hydrostatic pressure increased the growth rate of a number of fungal isolates showing that some sort of adaptive mechanism is present to be able to thrive under such conditions. Under temperature and salinity tests the filamentous fungal isolates shifted from non-halophilic to halotolerant when temperatures were increased from 25-35˚C and a few isolates of Fusarium and Penicillium shifted to complete halophily with increased temperature. 96% of the isolates had at least one gene involved in secondary metabolite synthesis. As genes for secondary metabolite can evolve rapidly the authors state this may confirm their hypothesis that there is some level of ecophysiological adaptation present.

This paper was laid out well and easy to follow. It mentioned in the introduction that there could be biotechnological potential in these deep see fungal isolates but further studies would be required to assess any validity in this claim as I do not believe this study provides evidence to support it. Overall I feel this paper could have gone into better detail when discussing the results but it is a good foundation for future marine fungal studies.

Paper reviewed:

Redou, V., Navarri, M., Meslet-Cladiere, L., Barbier, G., Burgaud, G. (2015). Species Richness And Adaptation Of Marine Fungi From Deep-Subseafloor Sediments. Applied and Environmental Microbiology 81(10) 3571-3583