Highly divergent 16S rRNA sequences in ribosomal operons of Scytonema hyalinum (Cyanobacteria).

Jeffrey R Johansen,Jan Zima,Nicole Pietrasiak,Jan Mareš,Tomáš Hauer,Markéta Bohunická,Lenka Štenclová

doi:10.1371/journal.pone.0186393

Jeffrey R Johansen, Jan Zima + Show 5 more

Open Access

PDF Available

https://doi.org/10.1371/journal.pone.0186393

Copy DOI

Export

Save

Cite

Abstract
Highlights/Summary
Full-Text PDF
Similar Papers

Abstract

Listen

A highly divergent 16S rRNA gene was found in one of the five ribosomal operons present in a species complex currently circumscribed as Scytonema hyalinum (Nostocales, Cyanobacteria) using clone libraries. If 16S rRNA sequence macroheterogeneity among ribosomal operons due to insertions, deletions or truncation is excluded, the sequence heterogeneity observed in S. hyalinum was the highest observed in any prokaryotic species thus far (7.3–9.0%). The secondary structure of the 16S rRNA molecules encoded by the two divergent operons was nearly identical, indicating possible functionality. The 23S rRNA gene was examined for a few strains in this complex, and it was also found to be highly divergent from the gene in Type 2 operons (8.7%), and likewise had nearly identical secondary structure between the Type 1 and Type 2 operons. Furthermore, the 16S-23S ITS showed marked differences consistent between operons among numerous strains. Both operons have promoter sequences that satisfy consensus requirements for functional prokaryotic transcription initiation. Horizontal gene transfer from another unknown heterocytous cyanobacterium is considered the most likely explanation for the origin of this molecule, but does not explain the ultimate origin of this sequence, which is very divergent from all 16S rRNA sequences found thus far in cyanobacteria. The divergent sequence is highly conserved among numerous strains of S. hyalinum, suggesting adaptive advantage and selective constraint of the divergent sequence.

Highlights

Small subunit rRNA gene sequence data have become critical for understanding microbial evolution, definition of taxa, estimating metagenomic diversity in localized environments, and estimating total microbial diversity on the planet [1,2,3]
We present evidence to show that 1) localized diversity possibly indicative of horizontal gene transfer (HGT) of an entire ribosomal operon exists in this cyanobacterial species cluster, 2) this putative HGT is an event that occurred prior to speciation within this species cluster, 3) secondary structure of the ribosomal rRNA of both subunits remains intact in the horizontally transferred operon, 4) gene conversion has not reversed the heterogeneity introduced by HGT, indicating that the introduced gene may increase fitness at the genus level
A nearly complete genome scaffold of Scytonema hyalinum HK-05 was sequenced by other authors (NCBI accession AP018194), and reported with seven separate plasmids, including a 16.3 kb plasmid containing a full ribosomal operon that is discussed in this paper (NCBI accession AP018198)

Summary

Introduction

Small subunit rRNA gene sequence data have become critical for understanding microbial evolution, definition of taxa, estimating metagenomic diversity in localized environments, and estimating total microbial diversity on the planet [1,2,3]. A nearly complete genome scaffold of Scytonema hyalinum HK-05 was sequenced by other authors (NCBI accession AP018194), and reported with seven separate plasmids, including a 16.3 kb plasmid containing a full ribosomal operon that is discussed in this paper (NCBI accession AP018198).

Results

Conclusion