Spatial and temporal distribution of archaeal diversity in meromictic, hypersaline Ocnei Lake (Transylvanian Basin, Romania)

Abstract

Saline, meromictic lakes with significant depth are usually formed as a result of salt mining activity. Ocnei Lake is one of the largest Transylvanian (Central Romania) neutral, hypersaline lake of man-made origin. We aimed to survey the seasonal dynamics of archaeal diversity in the water column of Ocnei Lake by employing microbiological methods as well as molecular techniques based on the sequence analysis of the 16S rRNA gene. We found that archaeal diversity in the water column increased with depth and salinity, with 8 OTUs being detected in the epilimnion compared to 21 found in the chemocline, and 32 OTUs in the monimolimnion. Down to 3.5 m depth, the archaeal community was markedly dominated by the presence of an unclassified archaeon sharing 93% sequence identity to Halogeometricum spp. At the chemocline, the shift in archaeal community composition was associated with an increase in salinity, the main factor affecting the vertical distribution of archaeal assemblages. It appears that the microoxic and hypersaline monimolimnion is populated by several major haloarchaeal taxa, with minor fluctuations in their relative abundances throughout all seasons. The culturable diversity was reasonably correlated to the dominant OTUs obtained by molecular methods. Our results indicate that Ocnei Lake represents a relatively stable extreme habitat, accommodating a diverse and putatively novel archaeal community, as 30% of OTUs could not be classified at the genus level.

Contrasting taxonomic stratification of microbial communities in two hypersaline meromictic lakes

“…The relative abundance of Archaea in the 0.5 (~2%) and 2 m (1.2%) depth assemblages was minor, and could be attributed to the lower salinity levels found at these depths (that is,~70 g l − 1 ). Similar findings were reported in other saline lakes (Yau et al, 2013;Baricz et al, 2014) or shallow ponds (Ghai et al, 2011), and are supported by the fact that most haloarchaeal species lyse at salt concentrations of o100 g l − 1 (Andrei et al, 2012). As the salinity increased over 240 g l − 1 (at 3.5 m depth) the proportion of the Archaea in the communities was higher, ranging between~20% (at 3.5 m depth) and~40% (at 9 m depth), but nonetheless lower than the bacterial one.…”

“…Even though the bacterial abundance was comparable to that typically described for high-salt environments (Demergasso et al, 2008;Baricz et al, 2014), the fact that they constituted~78% of the monimolimnion community was unanticipated, as previous studies reported the dominance of Archaea at salinities 4300 g l − 1 (Ghai et al, 2011;Baricz et al, 2014). We assume that the increased abundance of Bacteria in the deeper water strata could be achieved by outcompeting Archaea in suboxic hypersaline conditions, as the majority of halophilic archaeal species are aerobic (Andrei et al, 2012).…”

Extreme environments: microbiology leading to specialized metabolites

“…Phylogenetically diverse halophilic and highly halotolerant archaea are common in hypersaline systems and include members of the class Halobacteria (Andrei et al ). Extreme halophilic archaea have been isolated from hypersaline lakes in the Transylvanian Basin close to the salt minos of Turda (Baricz et al , ). Novel archaea isolated from commercial salt include Halarchaeum acidophilum (Minegishi et al ) and Natronoarchaeum mannanilyticum (Shimane et al ).…”

Patterns and Determinants of Halophilic Archaea (Class Halobacteria) Diversity in Tunisian Endorheic Salt Lakes and Sebkhet Systems

“…Further, we developed a pipeline for accurate phylogenetic assignment of obtained se-quences to the genus level by comparison to a curated database of validly described Halobacteria species using BLASTN (12). Within saline and hypersaline ecosystems, the level of and spatiotemporal fluctuations in salinity obviously play an important role in selection of taxa (34), although the impact of other factors, e.g., pH, temperature, physical characteristics, availability of dissolved O 2 , redox potential, and ionic composition (35), could not be discounted.…”