Abundant Taxa and Favorable Pathways in the Microbiome of Soda-Saline Lakes in Inner Mongolia.

Dahe Zhao,Songnian Hu,Jian Zhou,Junyu Chen,Yanning Zheng,Ming Li,Feiyue Cheng,Hua Xiang,Qiong Xue,Haiying Yu,Yaxin Zhu,Shengjie Zhang,Shuangjiang Liu

doi:10.3389/fmicb.2020.01740

Abstract

Soda-saline lakes are a special type of alkaline lake in which the chloride concentration is greater than the carbonate/bicarbonate concentration. Due to the high pH and a usually higher osmotic pressure than that of a normal soda lake, the microbes may need more energy to thrive in such a double-extreme environment. In this study, we systematically investigated the microbiome of the brine and sediment samples of nine artificially separated ponds (salinities from 5.5% to saturation) within two soda-saline lakes in Inner Mongolia of China, assisted by deep metagenomic sequencing. The main inorganic ions shaped the microbial community in both the brines and sediments, and the chloride concentration exhibited the most significant effect. A total of 385 metagenome-assembled genomes (MAGs) were generated, in which 38 MAGs were revealed as the abundant species in at least one of the eighteen different samples. Interestingly, these abundant species also represented the most branches of the microbiome of the soda-saline lakes at the phylum level. These abundant taxa were close relatives of microorganisms from classic soda lakes and neutral saline environments, but forming a combination of both habitats. Notably, approximately half of the abundant MAGs had the potential to drive dissimilatory sulfur cycling. These MAGs included four autotrophic Ectothiorhodospiraceae MAGs, one Cyanobacteria MAG and nine heterotrophic MAGs with the potential to oxidize sulfur, as well as four abundant MAGs containing genes for elemental sulfur respiration. The possible reason is that reductive sulfur compounds could provide additional energy for the related species, and reductions of oxidative sulfur compounds are more prone to occur under alkaline conditions which support the sulfur cycling. In addition, a unique 1,4-alpha-glucan phosphorylation pathway, but not a normal hydrolysis one, was found in the abundant Candidatus Nanohaloarchaeota MAG NHA-1, which would produce more energy in polysaccharide degradation. In summary, this work has revealed the abundant taxa and favorable pathways in the soda-saline lakes, indicating that efficient energy regeneration pathway may increase the capacity for environmental adaptation in such saline-alkaline environments. These findings may help to elucidate the relationship between microbial metabolism and adaptation to extreme environments.

Highlights

A soda lake is a type of saline lake with extremely high pH and salinity mainly due to high concentrations of carbonate/bicarbonate (Grant and Sorokin, 2011; Boros and Kolpakova, 2018)
CO32− and HCO3− concentrations ranged from 78.33 to 820 mM and from 80.33 to 385.25 mM, respectively, while the chloride concentrations were 1.5–2.4 times as much as the sum of both. Both DK and HC were classified as soda-saline lakes of the chloridecarbonate-sulfate type (Boros and Kolpakova, 2018) and will be called soda-saline lakes in the text
We summarized the metabolic potential of these abundant metagenomeassembled genomes (MAGs) in Supplementary Table 6

Summary

Introduction

A soda lake is a type of saline lake with extremely high pH and salinity mainly due to high concentrations (exceeding an equivalent percentage of 25) of carbonate/bicarbonate (Grant and Sorokin, 2011; Boros and Kolpakova, 2018). It is defined as “soda” type when the sum of bicarbonate and carbonate concentrations are the first in the rank of dominant ions, and is “soda-saline” type when the concentration of other ions is higher than that of bicarbonate/carbonate (Boros and Kolpakova, 2018) In these saline and alkaline environments, microorganisms exhibit surprisingly high biodiversity (Grant, 2006; Mesbah et al, 2007; Asao et al, 2011; Lanzen et al, 2013), relatively high primary productivity rates (Melack and Kilham, 1974; Melack, 1981; Kompantseva et al, 2009; Antony et al, 2013; Zorz et al, 2019), vigorous oxidation and reduction reactions of sulfur (Sorokin et al, 2010, 2011; Stam et al, 2010; Tourova et al, 2013; Vavourakis et al, 2019), and elevated metabolic activity of cellulose, methane, nitrogen and arsenic (Iversen et al, 1987; Carini and Joye, 2008; Oremland et al, 2017; Phitsuwan et al, 2019). This would support the microbes inhabiting such alkaline and saline environments, and playing important roles in the elemental cycling (Sorokin et al, 2014)

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Conclusion