title: The deletion of rnhB in Mycobacterium smegmatis does not affect the level of RNase HII substrates or influence genome stability.
abstract: RNase HII removes RNA from RNA/DNA hybrids, such as single ribonucleotides and RNA primers generated during DNA synthesis. Both, RNase HII substrates and RNase HII deficiency have been associated with genome instability in several organisms, and genome instability is a major force leading to the acquisition of drug resistance in bacteria. Understanding the mechanisms that underlie this phenomenon is one of the challenges in identifying efficient methods to combat bacterial pathogens. The aim of the present study was set to investigate the role of rnhB, presumably encoding RNase HII, in maintaining genome stability in the M. tuberculosis model organism Mycobacterium smegmatis. We performed gene replacement through homologous recombination to obtain mutant strains of Mycobacterium smegmatis lacking the rnhB gene. The mutants did not present an altered phenotype, according to the growth rate in liquid culture or susceptibility to hydroxyurea, and did not show an increase in the spontaneous mutation rate, determined using the Luria-Delbrück fluctuation test for streptomycin resistance in bacteria. The mutants also did not present an increase in the level of RNase HII substrates, measured as the level of alkaline degradation of chromosomal DNA or determined through immunodetection. We conclude that proteins other than RnhB proteins efficiently remove RNase HII substrates in M. smegmatis. These results highlight differences in the basic biology between Mycobacteria and eukaryotes and between different species of bacteria.
authors.affiliation: Department of Genetics and Physiology of Mycobacterium, Institute of Medical Biology, Polish Academy of Sciences, Lodz, Poland; Department of Microbiology, Biotechnology and Immunology, University of Lodz, Lodz, Poland.
authors.forename: Alina E
authors.initials: AE
authors.lastname: Minias
authors.affiliation: Department of Genetics and Physiology of Mycobacterium, Institute of Medical Biology, Polish Academy of Sciences, Lodz, Poland.
authors.forename: Anna M
authors.initials: AM
authors.lastname: Brzostek
authors.affiliation: Department of Teacher Training and Biodiversity Studies, University of Lodz, Lodz, Poland.
authors.forename: Piotr
authors.initials: P
authors.lastname: Minias
authors.affiliation: Department of Genetics and Physiology of Mycobacterium, Institute of Medical Biology, Polish Academy of Sciences, Lodz, Poland.
authors.forename: Jaroslaw
authors.initials: J
authors.lastname: Dziadek
mesh_terms: D000595:Amino Acid Sequence; D017353:Gene Deletion; D016680:Genome, Bacterial; D042822:Genomic Instability; D008969:Molecular Sequence Data; D009154:Mutation; D020102:Mycobacterium smegmatis / Q000235:genetics* / Q000378:metabolism*; D010641:Phenotype; D054730:Protein Interaction Domains and Motifs; D016914:Ribonuclease H / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism*; D016415:Sequence Alignment; D013379:Substrate Specificity
chemical_list: C091139:ribonuclease HII; D016914:Ribonuclease H