Changes in bacterial and archaeal communities during the concentration of brine at the graduation towers in Ciechocinek spa (Poland)

Abstract

This study evaluates the changes in bacterial and archaeal community structure during the gradual evaporation of water from the brine (extracted from subsurface Jurassic deposits) in the system of graduation towers located in Ciechocinek spa, Poland. The communities were assessed with 16S rRNA gene sequencing (MiSeq, Illumina) and microscopic methods. The microbial cell density determined by direct cell count was at the order of magnitude of 10⁷ cells/mL. It was found that increasing salt concentration was positively correlated with both the cell counts, and species-level diversity of bacterial and archaeal communities. The archaeal community was mostly constituted by members of the phylum Euryarchaeota, class Halobacteria and was dominated by Halorubrum-related sequences. The bacterial community was more diverse, with representatives of the phyla Proteobacteria and Bacteroidetes as the most abundant. The proportion of Proteobacteria decreased with increasing salt concentration, while the proportion of Bacteroidetes increased significantly in the more concentrated samples. Representatives of the genera Idiomarina, Psychroflexus, Roseovarius, and Marinobacter appeared to be tolerant to changes of salinity. During the brine concentration, the relative abundances of Sphingobium and Sphingomonas were significantly decreased and the raised contributions of genera Fabibacter and Fodinibius were observed. The high proportion of novel (not identified at 97% similarity level) bacterial reads (up to 42%) in the 16S rRNA gene sequences indicated that potentially new bacterial taxa inhabit this unique environment.

Keywords: Archaeal community; Bacterial community; Brine; Halophiles.

Fig. 1

Outlook of the sampling sites

Fig. 2

A graduation tower: a schematic diagram (a) arrows indicate the brine flow; photo (b)

Fig. 3

Phylum and genus level distribution of NGS reads within the domain Bacteria in the brine samples from Ciechocinek

Fig. 4

Phylum and genus level distribution of NGS reads within the domain Archaea in the brine samples from Ciechocinek

Fig. 5

Principal coordinates analysis (PCoA) of the bacterial (a) and archaeal (b) communities based on the Bray–Curtis distance matrix

Fig. 6

Venn diagrams of shared bacterial (a) and archaeal (b) OTUs at 0.03 dissimilarity level