Influence of Environmental Drivers and Potential Interactions on the Distribution of Microbial Communities From Three Permanently Stratified Antarctic Lakes.

Wei Li,Rachael M Morgan-Kiss

doi:10.3389/fmicb.2019.01067

Wei Li, Rachael M Morgan-Kiss

Open Access

https://doi.org/10.3389/fmicb.2019.01067

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Abstract

The McMurdo Dry Valley (MDV) lakes represent unique habitats in the microbial world. Perennial ice covers protect liquid water columns from either significant allochthonous inputs or seasonal mixing, resulting in centuries of stable biogeochemistry. Extreme environmental conditions including low seasonal photosynthetically active radiation (PAR), near freezing temperatures, and oligotrophy have precluded higher trophic levels from the food webs. Despite these limitations, diverse microbial life flourishes in the stratified water columns, including Archaea, bacteria, fungi, protists, and viruses. While a few recent studies have applied next generation sequencing, a thorough understanding of the MDV lake microbial diversity and community structure is currently lacking. Here we used Illumina MiSeq sequencing of the 16S and 18S rRNA genes combined with a microscopic survey of key eukaryotes to compare the community structure and potential interactions among the bacterial and eukaryal communities within the water columns of Lakes Bonney (east and west lobes, ELB, and WLB, respectively) and Fryxell (FRX). Communities were distinct between the upper, oxic layers and the dark, anoxic waters, particularly among the bacterial communities residing in WLB and FRX. Both eukaryal and bacterial community structure was influenced by different biogeochemical parameters in the oxic and anoxic zones. Bacteria formed complex interaction networks which were lake-specific. Several eukaryotes exhibit potential interactions with bacteria in ELB and WLB, while interactions between these groups in the more productive FRX were relatively rare.

Highlights

In aquatic ecosystems, the microbial loop plays a central role in fixation and transformation of energy and carbon, and the cycling of major nutrients
Microbial eukaryotes occupy critical roles in the McMurdo Dry Valley (MDV) food web as both the major primary producers and the top predators in the trophic cascade (Priscu et al, 1999; Bielewicz et al, 2011). This present study extends the current view of the MDV lake microbial communities by examining both bacterial and eukaryal community structure across a larger number of replicated samples collected from the entire water column of three thoroughly characterized MDV lakes
A full understanding of vertical distribution patterns in microbial communities within the stratified aquatic environment of the MDV lakes has been limited by a lack of sampling depths spanning the full water column, as well as a general absence of 18S rRNA sequences

Summary

Introduction

The microbial loop plays a central role in fixation and transformation of energy and carbon, and the cycling of major nutrients. Complex networks among the representatives of the microbial loop (viruses, Bacteria, Archaea, and microbial eukaryotes) have major implications on the global carbon cycle and other biogeochemical cycles 1998; Cotner and Biddanda, 2002; Fenchel, 2008; Jiao et al, 2010) Investigating both microbial diversity and community structure is a crucial first step in understanding ecological functioning in aquatic environments. Antarctic meromictic lakes are important sentinels of climate change and represent unique opportunities for investigating the impact of environmental drivers on microbial community structure and interactions within the microbial loop (Van Der Gucht et al, 2007; Eiler et al, 2012; Gulati et al, 2017)

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