Diversity and N2O Production Potential of Fungi in an Oceanic Oxygen Minimum Zone

Abstract

Fungi in terrestrial environments are known to play a key role in carbon and nitrogen biogeochemistry and exhibit high diversity. In contrast, the diversity and function of fungi in the ocean has remained underexplored and largely neglected. In the eastern tropical North Pacific oxygen minimum zone, we examined the fungal diversity by sequencing the internal transcribed spacer region 2 (ITS2) and mining a metagenome dataset collected from the same region. Additionally, we coupled 15N-tracer experiments with a selective inhibition method to determine the potential contribution of marine fungi to nitrous oxide (N2O) production. Fungal communities evaluated by ITS2 sequencing were dominated by the phyla Basidiomycota and Ascomycota at most depths. However, the metagenome dataset showed that about one third of the fungal community belong to early-diverging phyla. Fungal N2O production rates peaked at the oxic–anoxic interface of the water column, and when integrated from the oxycline to the top of the anoxic depths, fungi accounted for 18–22% of total N2O production. Our findings highlight the limitation of ITS-based methods typically used to investigate terrestrial fungal diversity and indicate that fungi may play an active role in marine nitrogen cycling.

Protein cycling in the eastern tropical North Pacific oxygen‐deficient zone: A de novo‐discovery peptidomic approach

“…Using different techniques, fungi have been found in other lowoxygen marine environments including the coastal upwelling system of Peru (hyphal chitin staining; Gutiérrez et al 2011), and in anoxic sediments of the Arabian Sea (Stief et al 2014). Recently, Peng and Valentine (2021) evaluated the diversity of free living and particle-associated (> 22 μm) fungi in the ETNP ODZ, also finding fungi to be dominated by Basidiomycota and Ascomycota at most depths, consistent with our de novodiscovery results.…”

“…Peptides specifically identifying the filamentous genus Aspergillus were found in all samples of this study except the deepest suspended POM (Table S7), as were numerous other filamentous and hyphae-producing groups of fungi and nonfungi (Actinobacteria, Oomycota). Although it is unknown how important fungal nitrogen cycling may be in the water column of the ODZ, Peng and Valentine (2021) recently demonstrated using 15 N-tracer incubations that fungal N 2 O production peaked at the upper oxic-anoxic interface in the ENTP ODZ water column. Our findings demonstrate that fungal peptides can be extracted and identified from marine POM via metaproteomic techniques.…”

The Response of Airborne Mycobiome to Dust Storms in the Eastern Mediterranean

“…Our data indicate that fungi can constitute up to 18% of the microbial community in the PM10 part of the air microbiome. This ratio is one to two orders of magnitude higher than what has been reported for the water column of the open ocean, where fungal reads were up to 0.2% of the total metagenomes [62]. This difference suggests that atmospheric transport is a potential mechanism for fungal dispersal from land to sea, an idea that has been suggested for bacterial dispersal [8,24], and is consistent with the positive correlation between the relative abundance of bacterial/archaeal reads and PM10 concentrations in this study (Figure 2).…”

Identifying the Sources and Drivers of Nitrous Oxide Accumulation in the Eddy‐Influenced Eastern Tropical North Pacific Oxygen‐Deficient Zone

“…Peng and Valentine (2021) recently suggested a potential niche for fungal denitrification in the ETNP at 0.0 < [O 2 ] < 0.93 μM and found that it contributes significantly to N 2 O production in the water column. Because fungi produce N 2 O with an SP ranging from ∼15‰ to ∼37‰ (Maeda et al., 2015; Rohe et al., 2014; Sutka et al., 2008), fungal denitrification could partly account for inferred N 2 O production via denitrification with a nonzero SP.…”