Abstract
We have used RNASeq and qRT-PCR to study mRNA levels for all σ-factors in different Mycobacterium marinum strains under various growth and stress conditions. We also studied their levels in M. marinum from infected fish and mosquito larvae. The annotated σ-factors were expressed and transcripts varied in relation to growth and stress conditions. Some were highly abundant such as sigA, sigB, sigC, sigD, sigE and sigH while others were not. The σ-factor mRNA profiles were similar after heat stress, during infection of fish and mosquito larvae. The similarity also applies to some of the known heat shock genes such as the α-crystallin gene. Therefore, it seems probable that the physiological state of M. marinum is similar when exposed to these different conditions. Moreover, the mosquito larvae data suggest that this is the state that the fish encounter when infected, at least with respect to σ-factor mRNA levels. Comparative genomic analysis of σ-factor gene localizations in three M. marinum strains and Mycobacterium tuberculosis H37Rv revealed chromosomal rearrangements that changed the localization of especially sigA, sigB, sigD, sigE, sigF and sigJ after the divergence of these two species. This may explain the variation in species-specific expression upon exposure to different growth conditions.
Highlights
The transcription machinery in bacteria, RNA polymerase, is composed of several subunits referred to as the α, β, β', σ- and ω-subunits [1] where the accessory σ-factor has a key role during initiation of transcription
Compared to the M. tuberculosis H37Rv strain, the CCUG-strain has four additional σ-factor genes—MMAR0975, MMAR3276, MMAR3687 and MMAR4487 –but it lacks the σ-factor gene corresponding to the M-strain MMAR2997 σ-factor (Fig 1B)
The gene synteny for the σ-factor genes that are present in the CCUG-strain is the same as that for the M. marinum M-strain
Summary
The transcription machinery in bacteria, RNA polymerase, is composed of several subunits referred to as the α-, β-, β'-, σ- and ω-subunits [1] where the accessory σ-factor has a key role during initiation of transcription. Two sigma (σ) factor families have been well characterized in bacteria, the σ70 and σ54 families. On the basis of phylogenetic relationship, the σ70 family can be divided into four groups depending on the presence or absence of specific regions; group 1. Expression and Regulation of Sigma Factors in Mycobacteria awards to Wind River Conferences, Louisiana Graduate Fellowship award and funds for supplies and travel by the University of Louisiana Graduate Student Organization to KMR and MNC. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript
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