Abstract
Two-component regulatory systems (TCSs) play pivotal roles in bacteria sensing many different stimuli from environment. Here, we investigated the role of the LytSR TCS in spore formation in Bacillus thuringiensis (Bt) subsp. kurstaki HD73. lacZ gene fusions revealed that the transcription of the downstream genes, lrgAB, encoding two putative membrane-associated proteins, is regulated by LytSR. The sporulation efficiency of a lytSR mutant was significantly lower than that of wild-type HD73. A confocal microscopic analysis demonstrated that LytSR modulates the process of forespore engulfment. Moreover, the transcription of the lytSR operon is regulated by the mother-cell transcription factor SigE, whereas the transcription of the sporulation gene spoIIP was reduced in the lytSR mutant, as demonstrated with a β-galactosidase activity assay. These results suggest that LytSR modulates forespore engulfment by affecting the transcription of the spoIIP gene in Bt.
Highlights
As a type of specialized differentiated cell, spores are used by Bacillus to survive starvation and harsh conditions
The results of the β-galactosidase assay showed that the transcriptional activity of PlrgAB increased from T4 to T8 in the HD73 strain in SSM, whereas it did not increase dramatically in the HD lytSR mutant (Figure 1B), suggesting that the transcription of the lrgAB genes is positively regulated by LytSR during the late sporulation process
The sporulation efficiency assay and a confocal microscopic analysis showed that spore formation was unaffected in the Bacillus thuringiensis (Bt) lrgAB mutant. This differs from the dramatic impact of this mutation on sporulation efficiency observed in B. anthracis (Chandramohan et al, 2009), orthologues of the lrgAB locus of Bt HD73 are conserved in the genomes of the B. cereus group (Supplementary Figure 2)
Summary
As a type of specialized differentiated cell, spores are used by Bacillus to survive starvation and harsh conditions. ΣF and σE, are instrumental in setting the cell-specific programs of gene expression in motion. Some σE- and σF-dependent genes are involved in the prespore engulfment process (Errington, 2003). The completion of engulfment is a key event governing the later stages of spore development. A third sporulation-specific sigma factor, σG, becomes active at this time, and this sigma factor controls the final stages of development inside the spore. The final mother–cell-specific sigma factor, σK, is regulated at multiple levels and is involved in the formation of the spore coat and in spore maturation (Errington, 2003; Hilbert and Piggot, 2004)
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