MamA essentiality in Mycobacterium smegmatis is explained by the presence of an apparent cognate restriction endonucleas
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BMC Research Notes Open Access
RESEARCH NOTE
MamA essentiality in Mycobacterium smegmatis is explained by the presence of an apparent cognate restriction endonuclease Samantha E. Randall1†, Maria Carla Martini1†, Ying Zhou1, Samantha R. Joubran1 and Scarlet S. Shell1,2*
Abstract Objective: Restriction-Modification (R-M) systems are ubiquitous in bacteria and were considered for years as rudimentary immune systems that protect bacterial cells from foreign DNA. Currently, these R-M systems are recognized as important players in global gene expression and other cellular processes such us virulence and evolution of genomes. Here, we report the role of the unique DNA methyltransferase in Mycobacterium smegmatis, which shows a moderate degree of sequence similarity to MamA, a previously characterized methyltransferase that affects gene expression in Mycobacterium tuberculosis and is important for survival under hypoxic conditions. Results: We found that depletion of mamA levels impairs growth and produces elongated cell bodies. Microscopy revealed irregular septation and unevenly distributed DNA, with large areas devoid of DNA and small DNA-free cells. Deletion of MSMEG_3214, a predicted endonuclease-encoding gene co-transcribed with mamA, restored the WT growth phenotype in a mamA-depleted background. Our results suggest that the mamA-depletion phenotype can be explained by DNA cleavage by the apparent cognate restriction endonuclease MSMEG_3214. In addition, in silico analysis predicts that both MamA methyltransferase and MSMEG_3214 endonuclease recognize the same palindromic DNA sequence. We propose that MamA and MSMEG_3214 constitute a previously undescribed R-M system in M. smegmatis. Keywords: Mycobacterium smegmatis, MamA, Restriction-Modification system, DNA methylation, Methyltransferase Introduction The primary role of bacterial Restriction-Modification (R-M) systems has typically been viewed as protection from foreign DNA, such as plasmids and phages. However, further work revealed these systems can have other important functions, including regulation of gene
*Correspondence: [email protected] † Samantha E. Randall and Maria Carla Martini contributed equally to this work 1 Department of Biology & Biotechnology, Worcester Polytechnic Institute, Worcester, MA, USA Full list of author information is available at the end of the article
expression and promoting bacterial evolution by enhancing DNA recombination [1–4]. To date, no complete R-M systems have been defined in M. tuberculosis, the causative agent of tuberculosis, or in its non-pathogenic relative M. smegmatis, a model system widely used to study the basic biology of M. tuberculosis. We previously identified and characterized one of the three predicted DNA methyltransferases in M. tuberculosis, MamA [5], which is non-essential for M. tuberculosis survival in vitro and during infection [6–8]. We and others showed that MamA is an adenine methyltransferase that affects expression of a number of genes in M. tuberculosis during log phase growth and promot
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