Transcriptional analysis of ftsZ within the dcw cluster in Bacillus mycoides

Tiziana Santini,Luana Turchi,Carmen Di Franco,Giulia Ceccarelli,E Beccari

doi:10.1186/1471-2180-13-27

Abstract

BackgroundIn Bacillus mycoides, as well as in other members of the B. cereus group, the tubulin-like protein of the division septum FtsZ is encoded by the distal gene of the cluster division and cell wall (dcw). Along the cluster the genes coding for structural proteins of the division apparatus are intermingled with those coding for enzymes of peptidoglycan biosynthesis, raising the possibility that genes with this different function might be coexpressed. Transcription of ftsZ in two model bacteria had been reported to differ: in B. subtilis, the ftsZ gene was found transcribed as a bigenic mRNA in the AZ operon; in E. coli, the transcripts of ftsZ were monogenic, expressed by specific promoters. Here we analyzed the size and the initiation sites of RNAs transcribed from ftsZ and from other cluster genes in two B. mycoides strains, DX and SIN, characterized by colonies of different chirality and density, to explore the correlation of the different morphotypes with transcription of the dcw genes.ResultsIn both strains, during vegetative growth, the ftsZ-specific RNAs were composed mainly of ftsZ, ftsA-ftsZ and ftsQ-ftsA-ftsZ transcripts. A low number of RNA molecules included the sequences of the upstream murG and murB genes, which are involved in peptidoglycan synthesis. No cotranscription was detected between ftsZ and the downstream genes of the SpoIIG cluster. The monogenic ftsZ RNA was found in both strains, with the main initiation site located inside the ftsA coding sequence. To confirm the promoter property of the site, a B. mycoides construct carrying the ftsA region in front of the shortened ftsZ gene was inserted into the AmyE locus of B. subtilis 168. The promoter site in the ftsA region was recognized in the heterologous cellular context and expressed as in B. mycoides.ConclusionsThe DX and SIN strains of B. mycoides display very similar RNA transcription specificity. The ftsZ messenger RNA can be found either as an independent transcript or expressed together with ftsA and ftsQ and, in low amounts, with genes that are specific to peptidoglycan biosynthesis.

Highlights

In Bacillus mycoides, as well as in other members of the B. cereus group, the tubulin-like protein of the division septum FtsZ is encoded by the distal gene of the cluster division and cell wall
The ftsZ DNA probe detected three main RNA components in SIN and DX: the shortest one, found just below the position of the 16S B. mycoides ribosomal RNA (1530 nucleotides), was the size of the monogenic transcript, since the ftsZ coding region spans 1155 nucleotides from the starting ATG to the termination triplet; the second hybridization band, below the 23S ribosomal RNA (2907 nucleotides), harbored transcripts with the length of ftsA plus ftsZ; the third band, in the upper part of the gel, carried RNAs corresponding to the size of three genes, ftsQ-ftsA-ftsZ since ftsZ is not cotranscribed with downstream genes
The fastest one migrated slightly less than the monogenic ftsZ RNA band, which is in keeping with the 144 bp longer coding sequence of the ftsA gene; the second ftsA-specific band colocalized with the ftsZ bicistronic transcripts; the third band in the uppermost position was broader and more intense than the other two bands, indicating that ftsA was abundant in long transcripts, mostly ftsQ-ftsAftsZ RNA

Summary

Introduction

In Bacillus mycoides, as well as in other members of the B. cereus group, the tubulin-like protein of the division septum FtsZ is encoded by the distal gene of the cluster division and cell wall (dcw). A Gram positive soil rod bacillus of the B. cereus species-group [1], is characterized by hyphal colonies with cells connected at the poles in long filaments. These filaments converge into bundles that mainly curve clock- or counter-clockwise in two kinds of bacilli, both of which were attributed to B. mycoides [2]. A very limited number of DX and SIN nucleotides differs along the dcw region This points to a close evolutionary relationship between the two strains as well as between the members of the B. cereus group. Comparative genome analysis of a large number of bacilli attributed to the group recently led to the proposal that they should be classified as a single species [1]

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Conclusion