Vertical stratification of bacteria and archaea in sediments of a small boreal humic lake.

Antti J Rissanen,Hannu Nykänen,Anita Mäki,Marja Tiirola,Sari Peura,Promise A Mpamah,Christina Biasi,Sami Taipale

doi:10.1093/femsle/fnz044

Antti J Rissanen, Hannu Nykänen + Show 6 more

Open Access

https://doi.org/10.1093/femsle/fnz044

Copy DOI

Abstract

ABSTRACTAlthough sediments of small boreal humic lakes are important carbon stores and greenhouse gas sources, the composition and structuring mechanisms of their microbial communities have remained understudied. We analyzed the vertical profiles of microbial biomass indicators (PLFAs, DNA and RNA) and the bacterial and archaeal community composition (sequencing of 16S rRNA gene amplicons and qPCR of mcrA) in sediment cores collected from a typical small boreal lake. While microbial biomass decreased with sediment depth, viable microbes (RNA and PLFA) were present all through the profiles. The vertical stratification patterns of the bacterial and archaeal communities resembled those in marine sediments with well-characterized groups (e.g. Methanomicrobia, Proteobacteria, Cyanobacteria, Bacteroidetes) dominating in the surface sediment and being replaced by poorly-known groups (e.g. Bathyarchaeota, Aminicenantes and Caldiserica) in the deeper layers. The results also suggested that, similar to marine systems, the deep bacterial and archaeal communities were predominantly assembled by selective survival of taxa able to persist in the low energy conditions. Methanotrophs were rare, further corroborating the role of these methanogen-rich sediments as important methane emitters. Based on their taxonomy, the deep-dwelling groups were putatively organo-heterotrophic, organo-autotrophic and/or acetogenic and thus may contribute to changes in the lake sediment carbon storage.

Highlights

A large number of small humic forest lakes are typical for the boreal region (Downing et al 2006)
As nucleic acids originate from both eukaryotes and prokaryotes and branched fatty acids (BrFA) only from bacteria, the difference in the vertical distribution of nucleic acids and BrFAs may be partially explained by steeper decrease in eukaryotic biomass than in bacterial biomass (Wurzbacher et al 2017)
Based on results from the boreal study lake and the previously studied temperate lakes, it can be concluded that lake sediment bacterial and archaeal communities generally follow a similar stratification pattern as communities in marine systems with the relative importance of poorly-known groups increasing with depth

Summary

Introduction

A large number of small humic forest lakes are typical for the boreal region (Downing et al 2006). The few existing lake sediment studies from the temperate area indicate that the stratification patterns of the abundance and composition of microbial communities differ between lakes (Koizumi, Kojima and Fukui 2003; Ye et al 2009; Borrel et al 2012; Wurzbacher et al 2017). The composition of bacterial and archaeal communities changed considerably and the abundance of microbes (concentration of DNA and cells) decreased with sediment depth in Lake Stechlin (Wurzbacher et al 2017). Further studies are needed to confirm this as well as to explore, whether and how the bacterial and archaeal community changes in the low-energy conditions below the zone dominated by methanogens

Objectives

Methods

Results

Conclusion