Hypersaline sapropels act as hotspots for microbial dark matter

Abstract

Present-day terrestrial analogue sites are crucial ground truth proxies for studying life in geochemical conditions close to those assumed to be present on early Earth or inferred to exist on other celestial bodies (e.g. Mars, Europa). Although hypersaline sapropels are border-of-life habitats with moderate occurrence, their microbiological and physicochemical characterization lags behind. Here, we study the diversity of life under low water activity by describing the prokaryotic communities from two disparate hypersaline sapropels (Transylvanian Basin, Romania) in relation to geochemical milieu and pore water chemistry, while inferring their role in carbon cycling by matching taxa to known taxon-specific biogeochemical functions. The polyphasic approach combined deep coverage SSU rRNA gene amplicon sequencing and bioinformatics with RT-qPCR and physicochemical investigations. We found that sapropels developed an analogous elemental milieu and harbored prokaryotes affiliated with fifty-nine phyla, among which the most abundant were Proteobacteria, Bacteroidetes and Chloroflexi. Containing thirty-two candidate divisions and possibly undocumented prokaryotic lineages, the hypersaline sapropels were found to accommodate one of the most diverse and novel ecosystems reported to date and may contribute to completing the phylogenetic branching of the tree of life.

Limnology and plankton diversity of salt lakes from Transylvanian Basin (Romania): A review

“…), extremely halophilic heterotrophic clostridia (Halanaerobiaceae, Halanaerobacteroidaceae, and Clostridiaceae) and spirochaetes (Spirochaetaceae) dominated among dnA metabarcodinginferred taxa. intriguingly, sequences pertaining to uncultured or unclassified bacterial divisions (e.g., oP1/Acetothermia, od1/Parcubacteria) were found at significant (1-2%) abundances in the water columns and organic-rich sediments of ursu and Fără Fund lakes (Andrei et al, 2015;2017b). to our knowledge, the transylvanian deep, hypersaline, and perennially stratified aquatic systems have no match with analogous lakes worldwide.…”

“…), Msbl1 candidate division, and thermoplasmata (Máthé et al, 2014;Andrei et al, 2015) N o n -c o m m e r c i a l u s e o n l y 27 Plankton diversity in transylvanian salt lakes in ursu and Fără Fund lakes, whereas reads related to uncultured archaeal divisions were detected in anaerobic layers of ursu (Parvarchaea), Fără Fund (Parvarchaea and nanohaloarchaea) (Andrei et al, 2015) and brâncoveanu (nanohaloarchaea) (Andrei et al, 2017a) lakes, respectively. Additionally, Parvarchaea was suggested as abundant component of microbial communities from hypersaline organic-rich sediments (sapropels) of ursu and Fără Fund lakes (Andrei et al, 2017b). the ultrasmall-sized (<0.8 μm) nanohaloarchaea were identified by de novo assembly of metagenomes from hypersaline lakes (lake tyrell, Australia) and halite nodules (Atacama desert) where they appear to thrive under aerobic and hypersaline conditions alongside members of Halobacteria (Ghai et al, 2011;narasingarao et al, 2012;Podell et al, 2013;crits-cristoph et al, 2016).…”

“…were isolated from the shallow and moderately saline Mierlei and roșu lakes (2-15% salinity, 2 m maximum depth) as well as from the mixolimnion of ursu lake (2-10% total salinity) (borsodi et al, 2013;crognale et al, 2013;Máthé et al, 2014). insights into bacterial community composition were further retrieved by 16s rrnA gene clone library and dGGe in Mierlei, roșu, and ursu lakes (borsodi et al, 2013;crognale et al, 2013;Máthé et al, 2014) whereas a deeper resolution of microbial diversity along the water columns and sediments of ursu and Fără Fund was gained by dnA metabarcoding analysis (Andrei et al, 2015;Andrei et al, 2017b). thus, in the oxic, moderately saline (2-13% salinity) water horizon of investigated lakes (Mierlei, roșu, ursu) in sovata, Tab.…”

Bioturbation of peanut worms Sipunculus nudus on the composition of prokaryotic communities in a tidal flat as revealed by 16S rRNA gene sequences

“…In the present study, Proteobacteria was also the most dominant phylum (Figure a), and a similar situation was found in other studies (Andrei et al, ; Ma et al, ; Shen et al, ; Zhang, Hu, Ren, & Zhang, ; Zhu, Wang, Zhang, Zhu, & Zou, ). However, the total number of bacterial phyla was similar to that in sandy tidal flat (18 phyla), wetland (20 phyla) and early biofilms (11 phyla) (Peng, Li, Lu, Xiao, & Yang, ; Shen et al, ; Zhu et al, ), but less than that in mudflats (53), hypersaline sapropels (59 phyla) and mangrove mudflats (57 phyla) (Ma et al, ; Andrei et al, ; Zhang, Hu, Ren, & Zhang, ), most likely because of the differences in the physicochemical properties and disturbances in the environments. The main reason for these relationships might also be that the organic matter content was lower, and the oxygen content was higher in the sandy tidal flat than in the other mudflat habitats.…”

The Saline Organic-Rich Sediments: a Short Overview

“…Surprisingly, the SSU rDNA metabarcoding analysis of environmental samples further suggested that representatives of thirty-two candidate divisions and possibly undocumented prokaryotic lineages might be present in the hypersaline sapropels of both lakes. Among the most abundant MDM members detected were OP1 ('Acetothermia'), OP3 ('Omnitrophica'), OD1 ('Parcubacteria'), WWE1 ('Cloacimonetes') and Parvarchaeota (Andrei et al, 2017). These microbes might be involved in the iron-cycling (Parvarchaeota (Fig.…”