Abstract
Fungal contributions to ecosystem processes are well documented for terrestrial systems yet oceans, which account for most of the Earth’s surface, have remained poorly explored with regards to organisms in this kingdom. Here, we demonstrate that, although in low relative abundance (i.e,. fungal reads made up 1.4-2.9% of the metagenomes), fungi contribute to both phylogenetic and functional microbial diversity with a conserved fungal presence in global marine samples. Universally distributed taxa and functions implicate them in complex carbon and fatty acid metabolism, with depth stratification along pelagic zones. Functional differences in observed genes between epipelagic and mesopelagic waters indicate changes in UV protection, shift to carbohydrate limited diets, as well as alternative energy sources. Metagenomic data also provided evidence for a latitudinal gradient in fungal diversity linked to temperature shifts. Our results suggest that fungi contribute to multiple biogeochemical cycles in the pelagic ocean, and could be integral for ecosystem functioning through provision of key nutrients.
Highlights
Modern marine microbial ecology has focused on the prokaryotic component, with other organisms such as fungi being understudied in comparison to their terrestrial counterparts
From the Microbial Observatory Time-Series (MOTS) transect, four samples were utilized for metagenomic sequencing representative of biological duplicates for surface waters within the nutrient-poor subtropical waters (STW) and the cold, macronutrient rich subAntarctic waters (SAW)
The “MOTS transect” has recently been used as a model system to study gradients at small scales leading to the identification of oceanic fronts as boundaries for microbial community changes (Baltar et al, 2015, 2016)
Summary
Modern marine microbial ecology has focused on the prokaryotic component, with other organisms such as fungi being understudied in comparison to their terrestrial counterparts. Despite detection of fungi in many different marine environments via metabarcoding, from sub-seafloor sediments to open ocean waters (Nagahama et al, 2003; Pang and Mitchell, 2005; Bass et al, 2007; Zuccaro et al, 2008; Gao et al, 2010; Jebaraj et al, 2010; Edgcomb et al, 2011; Amend et al, 2012; Jones and Pang, 2012; Richards et al, 2012; Burgaud et al, 2013; Rama et al, 2014; Wang et al, 2014; Yarden, 2014; Gutiérrez et al, 2016; Taylor and Cunliffe, 2016), their diversity and functions in the ocean remains largely unknown.
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