Cyanobacteria and Diatoms in Biofilms of Two Karstic Streams in Germany and Changes of Their Communities Along Calcite Saturation Gradients

Abstract

Biofilms microscopically dominated by cyanobacteria and diatoms of two CO₂ degassing karst-water creeks in Germany were investigated for their diversities along a gradient of calcification using SSU rRNA gene cloning and sequencing from environmental samples. The recovered totals of 731/413 cyanobacteria/diatom clones were grouped at 97/98% similarity levels into 28/29 molecular OTUs widely spread over their corresponding sequence phylogenies forming mostly monophyletic subclades. Sequence comparisons with named reference strains from NCBI/GenBank as well as newly determined references from the SAG culture collection left about half of the cyanobacteria OTUs still unidentified. Most of the diatom OTUs could be identified at least at the generic level. To improve identification also cultures of cyanobacteria and diatoms were established that allowed even species identification of some diatoms, but also revealed additional cyanobacteria hard to identify which were not recovered in the clone libraries. A significant correlation of the relative OTU abundances in clone libraries with values of SI_calcite was found and, therefore, redundancy analysis distinguished highly calcified sites far from the spring from those less calcified closer to the spring. The noncalcified spring sites were clearly distinct from all other sites by the presence of four cyanobacteria OTUs exclusively retrieved and that no diatoms could be recovered from there. Four cyanobacteria and three diatom OTUs were recovered whose increasing relative abundance per clone library was correlated with increasing calcification. This may indicate that not only cyanobacteria, but also diatoms are more directly involved in the biogenic impact on tufa formation than assumed previously.

Keywords:

• Cyanobacteria
• Diatoms
• karst-water stromatolites
• micro-algal community structure
• molecular operational taxonomic unit (OTU)
• small subunit ribosomal Redundancy Analysis (RDA)
• RNA (SSU rRNA)

Acknowledgments

We gratefully acknowledge Anke Behnke for the generation of diatom specific primers, Svenja Bruns for the establishment of diatom cultures, Andreas Reimer for providing hydrochemical data of hard-water creeks, Dorothea Hause-Reitner for maintaining the cultures of diatoms and cyanobacteria, Dominik Hepperle (Kleinraden) for provision of 18S rRNA gene sequencing primer sequences and Maike Lorenz for valuable comments, kind provision of strains and the deposition of cultures to the SAG culture collection. We thank two anonymous reviewers for their helpful and valuable suggestions and corrections.

Supplemental Material

Supplemental data for this article can be accessed on the publisher's website.

Funding

This project is part of the Research Unit 571“Geobiology of organo- and biofilms” funded by the German Research Foundation (DFG-FOR 571, Ar 335/5, FR905/13; publication # 66).