Nutrient Acquisition, Rather Than Stress Response Over Diel Cycles, Drives Microbial Transcription in a Hyper-Arid Namib Desert Soil.

Carlos León-Sobrino,Don A Cowan,Jean-Baptiste Ramond,Gillian Maggs-Kölling

doi:10.3389/fmicb.2019.01054

Carlos León-Sobrino, Don A Cowan + Show 2 more

Open Access

https://doi.org/10.3389/fmicb.2019.01054

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Abstract

Hot desert surface soils are characterized by extremely low water activities for large parts of any annual cycle. It is widely assumed that microbial processes in such soils are very limited. Here we present the first metatranscriptomic survey of microbial community function in a low water activity hyperarid desert soil. Sequencing of total mRNA revealed a diverse and active community, dominated by Actinobacteria. Metatranscriptomic analysis of samples taken at different times over 3 days indicated that functional diel variations were limited at the whole community level, and mostly affected the eukaryotic subpopulation which was induced during the cooler night hours. High levels of transcription of chemoautotrophic carbon fixation genes contrasted with limited expression of photosynthetic genes, indicating that chemoautotrophy is an important alternative to photosynthesis for carbon cycling in desiccated desert soils. Analysis of the transcriptional levels of key N-cycling genes provided strong evidence that soil nitrate was the dominant nitrogen input source. Transcriptional network analyses and taxon-resolved functional profiling suggested that nutrient acquisition processes, and not diurnal environmental variation, were the main drivers of community activity in hyperarid Namib Desert soil. While we also observed significant levels of expression of common stress response genes, these genes were not dominant hubs in the co-occurrence network.

Highlights

Arid lands are defined as having a level of precipitation (P) below the potential evapotranspiration (PET) level (P/PET < 1)
It is widely accepted that the extreme conditions in hot desert open soils limit both microbial and plant life (Pointing and Belnap, 2012; Makhalanyane et al, 2015) and that microbial activity is spatially fragmented, temporally limited and water-driven (Belnap et al, 2005; Pointing and Belnap, 2012; Collins et al, 2014)
We have demonstrated that a diverse and consistently active edaphic microbial community exists in hyperarid Namib Desert soils, and that the “active” community is dominated by non-photosynthetic bacteria

Summary

Introduction

Arid lands (deserts) are defined as having a level of precipitation (P) below the potential evapotranspiration (PET) level (P/PET < 1). Such lands cover an estimated one-third of Earth’s terrestrial surface (Laity, 2008) and are projected to expand in current climate change scenarios (Reich et al, 2001). 5 million years) continuously hyperarid (P/PET < 0.05) desert on Earth (Seely and Pallet, 2008). The microbial ecology of various Namib Desert edaphic niches has been extensively studied, highlighting the importance of water availability and soil chemistry ( phosphorus and ammonia) in microbial community assembly and function (Frossard et al, 2015; Ronca et al, 2015; Johnson et al, 2017; Scola et al, 2017)

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