A fungi hotspot deep down the ocean: explaining the presence of Gjaerumia minor in Equatorial Pacific bathypelagic waters

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A plant parasite associated with the white haze disease in apples, the Basidiomycota Gjaerumia minor, has been found in most samples of the global bathypelagic ocean. An analysis of environmental 18S rDNA sequences on 12 vertical profiles of the Malaspina 2010 expedition shows that the relative abundance of this cultured species actually increases with depth while its distribution is remarkably different between the deep waters of the Pacific and Atlantic oceans, being present in higher concentrations in the former. This is evident from sequence analysis and a microscopic survey with a species-specific newly designed TSA-FISH probe. Several hints point to the hypothesis that G. minor is transported to the deep ocean attached to particles, and the absence of G. minor in bathypelagic Atlantic waters could then be explained by the absence of this organism in surface waters of the equatorial Atlantic. The good correlation of G. minor biomass with recalcitrant carbon and free-living prokaryotic biomass in South Pacific waters, together with the identification of the observed cells as yeast and not as a resting spore (teliospore), point to the possibility that once arrived at deep layer this species keeps on growing and thriving.

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  1. Our results show, in accordance to previous works38,51, that the Bathypelagic Ocean is not an isolated environment but it is in continue connection with surface waters and with the land. In this regard the fungus G. minor shows an enormous potential to be an important active part of the global carbon cycle, pointing at the same time to the importance and necessity of more studies both on the Bathypelagic Ocean and on its fungal diversity.

    Very fascinating work! I'd never heard about these mysterious fungi before so it was fun to learn about them! Its amazing how these microbes thrive in wildly different environments! I'd be very interested to see if y'all are able to replicate the yeast-like morphology in lab settings by mimicking the marine environment. Dissecting the Atlantic vs Pacific impact further would be very cool for future studies! Thanks for sharing this neat work!

  2. TSA-FISH analysis targeting G. minor was performed on the deepest sample (between 2600 and 4000 m) of 34 stations.

    Do you think the morphological distribution would be different when taken from different ocean depths? I imagine the pressure differences could lead to morphological changes/adaptations.

    Also, are the yeast forms ever found in apples? or are those organisms most always elongated hyphae?

  3. The elongated morphotypes, present only in Pacific waters, are probably hyphae, sometimes found in chains

    I'm a bit confused. A few sentences above you said the yeast-like form never occurs in culture and now that the hyphae form is only in pacific waters. Does this mean neither morphologies are found in cultured cells?

    The cultured cells in Fig 1 appear to be elongated hyphae as well? Sorry if I'm misreading things.

    Edit: Oh! I see! Are you stating that, when in marine environments, the hyphae are only observed in the Pacific Ocean? In Fig 4 you show that there are no elongated morphotypes in the Atlantic Ocean and they are mostly observed in the Pacific Ocean; however, you do show their presence in the Indian Ocean as well, correct? I think this could be reworded for clarity