Bacterioplankton Community Composition Along Environmental Gradients in Lakes From Byers Peninsula (Maritime Antarctica) as Determined by Next-Generation Sequencing.

Antonio Picazo,Juan Antonio Villaescusa,Antonio Camacho,Antonio Quesada,Javier Miralles-Lorenzo,David Velázquez,Carlos Rochera

doi:10.3389/fmicb.2019.00908

Antonio Picazo, Juan Antonio Villaescusa + Show 5 more

Open Access

https://doi.org/10.3389/fmicb.2019.00908

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Abstract

This study comprises the first attempt to describe the planktonic bacterial communities of lakes from Byers Peninsula, one of the most significant limnological districts in the Maritime Antarctica, leveraging next-generation sequencing (NGS) technologies. For the survey, we selected 7 lakes covering the environmental gradient from inland to coastal lakes, some of them sampled both in surface and deep waters. Analysis provided just over 85,000 high quality sequences that were clustered into 864 unique Zero-radius Operational Taxonomic Units (ZOTUs) (i.e., 100% sequence similarity). Yet, several taxonomic uncertainties remained in the analysis likely suggesting the occurrence of local bacterial adaptations. The survey showed the dominance of the phyla Proteobacteria and Bacteroidetes. Among the former, the Gammaproteobacteria class, more specifically the order Betaproteobacteriales, was the dominant group, which seems to be a common trend in nutrient-limited Antarctic lakes. Most of the families and genera ubiquitously detected belonging to this class are indeed typical from ultra-oligotrophic environments, and commonly described as diazotrophs. On the other hand, among the members of the phylum Bacteroidetes, genera such as Flavobacterium were abundant in some of the shallowest lakes, thus demonstrating that also benthic and sediment-associated bacteria contributed to water bacterial assemblages. Ordination analyses sorted bacterial assemblages mainly based on the environmental gradients of nutrient availability and conductivity i.e., salinity. However, transient bacterial associations, that included the groups Clostridiaceae and Chloroflexi, also occurred as being forced by other drivers such as the influence of the nearby fauna and by the airborne microorganisms. As we intended, our NGS-based approach has provided a much greater resolution compared to the previous studies conducted in the area and confirmed to a large extent the previously obtained patterns, thus reinforcing the view of Byers as a hotspot of microbial biodiversity within Antarctica. This high microbial diversity allows the use of these aquatic ecosystems and their bacterial assemblages as sentinels for the monitoring of adaptive responses to climate change in this rapidly warming area.

Highlights

Environmental conditions in Antarctica impose severe restrictions to life
Historical surveys conducted in these lakes showed increasing abundances from inland to coastal sites following a trophic gradient (Figure 2), though the shallower lake of the plateau, Lake Somero, showed higher bacterial abundance as occurred for total phosphorus (TP) and Chl-a concentration
Lakes surveyed in Byers Peninsula include a variety of morphological features and trophic status ranging from ultraoligotrophic to eutrophic

Summary

Introduction

Environmental conditions in Antarctica impose severe restrictions to life. lakes there show relatively simple food webs and are dominated by microorganisms (Vincent and Laybourn-Parry(eds), 2008). The benthic compartment in these lakes has usually a main role (Quesada and Velázquez, 2012), but during the transition to the ice-free periods, the productivity in the water column is enhanced because the high availability of light and fluxes of allochthonous nutrients (López-Bueno et al, 2009; Rochera et al, 2010). During these periods, major changes are expected to occur in the composition of planktonic microbial assemblages. In a framework of global warning that affects severely to these ecosystems (Camacho et al, 2012), it arises as a need to assess to what extent these microbial communities are resilient to disturbances, and what are the major structuring forces (e.g., nutrients, dispersal, etc.)

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