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Misconception of Schizophyllum commune strain 20R-7-F01 origin from subseafloor sediments over 20 million years old

Summary

Researchers questioned whether a fungus found in ancient ocean sediments 2 km below the seafloor actually came from 20 million years ago or was modern contamination. By analyzing DNA repetitive sequences in different fungal populations, they discovered the strain was genetically almost identical to modern fungi from Asia, not ancient at all. The extreme conditions in the deep sediments would make it impossible for fungi to survive or exchange genes for millions of years, proving the fungus came from surface contamination during drilling rather than ancient times.

Background

Schizophyllum commune strain 20R-7-F01 was isolated from deep subseafloor sediments approximately 2 km below the ocean floor during Ocean Drilling Expedition 337, with sediments claimed to be over 20 million years old. The strain was proposed as a high-quality model for studying fungal evolution and environmental adaptation mechanisms in extreme deep-sea conditions.

Objective

To investigate the origin of S. commune strain 20R-7-F01 using simple sequence repeats (SSR) of DNA and determine whether the strain truly originated from ancient subseafloor sediments or represents terrestrial contamination.

Results

Strain 20R-7-F01 showed the highest genetic similarity (48.8% at trinucleotide motifs) with East Asian strains rather than temporal isolation expected from 20 million-year-old sediments. Multidimensional scaling revealed no signs of spatial and temporal isolation, with the strain clustering within modern East Asian populations and showing evidence of intensive recent genetic exchange.

Conclusion

The terrestrial origin of S. commune strain 20R-7-F01 is confirmed, with the Far East of the Russian Federation (approximately Khabarovsk, Primorsky Krai) identified as the probable place of origin. The extreme environmental conditions at 2 km depth make fungal growth and genetic exchange impossible, suggesting contamination from drilling fluid rather than indigenous ancient fungi.
  • Published in:Scientific Reports,
  • Study Type:Genomic Analysis Study,
  • Source: PMID: 39994251, DOI: 10.1038/s41598-024-84457-2
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