Maturing Mycobacterium smegmatis peptidoglycan requires non-canonical crosslinks to maintain shape
- Harvard TH Chan School of Public Health, United States
- Harvard Medical School, United States
- Swiss Federal Institute of Technology in Lausanne (EPFL), Switzerland
- Texas A&M University, United States
- Yale School of Medicine, United States
Abstract
In most well studied rod-shaped bacteria, peptidoglycan is primarily crosslinked by penicillin-binding proteins (PBPs). However, in mycobacteria, crosslinks formed by L,D-transpeptidases (LDTs) are highly abundant. To elucidate the role of these unusual crosslinks, we characterized Mycobacterium smegmatis cells lacking all LDTs. We find that crosslinks generate by LDTs are required for rod shape maintenance specifically at sites of aging cell wall, a byproduct of polar elongation. Asymmetric polar growth leads to a non-uniform distribution of these two types of crosslinks in a single cell. Consequently, in the absence of LDT-mediated crosslinks, PBP-catalyzed crosslinks become more important. Because of this, Mycobacterium tuberculosis (Mtb) is more rapidly killed using a combination of drugs capable of PBP- and LDT- inhibition. Thus, knowledge about the spatial and genetic relationship between drug targets can be exploited to more effectively treat this pathogen.
Data availability
Sequencing data were deposited into NCBI's Sequence Read Archive (SRA) under SRA study- SRP141343 https://www.ncbi.nlm.nih.gov/Traces/study/?acc=SRP141343
Article and author information
Author details
Catherine Baranowski
Haig A Eskandarian
Thomas G Bernhardt
Funding
National Institutes of Health (U19 AI107774)
- Thomas R Ioerger
- Eric J Rubin
National Institutes of Health (R01 GM76710)
- Suzanne Walker
National Institutes of Health (R01AI083365)
- Thomas G Bernhardt
National Institutes of Health (F32GM123579)
- Michael A Welsh
Swiss National Science Foundation (205321_134786)
- Georg E Fantner
Innovative Medicines Initiative (115337)
- John McKinney
EU-FP7/Eurostars (E!8213)
- Georg E Fantner
European Molecular Biology Organization (750-2016)
- Haig A Eskandarian
National Science Foundation (DGE0946799)
- Karen J Kieser
National Institutes of Health (U19AI109764)
- Thomas G Bernhardt
Swiss National Science Foundation (205320_152675)
- Georg E Fantner
Burroughs Wellcome Fund (Career Award at the Scientific Interface)
- E Hesper Rego
American Heart Association (14POST18480014)
- Lok-To Sham
Simons Foundation (Fellow of the Life Sciences Research Foundation Award)
- Hoong C Lim
Swiss National Science Foundation (310030_156945)
- John McKinney
European Union (FP7/2007-2013/ERC Grant agreement No. 307338 (NaMic))
- Georg E Fantner
European Molecular Biology Organization (191-2014)
- Haig A Eskandarian
National Science Foundation (DGE1144152)
- Karen J Kieser
National Institutes of Health (F32AI104287)
- E Hesper Rego
The funders had no role in study design, data collection and interpretation, or the decision to submit the work for publication.
Copyright
© 2018, Baranowski et al.
This article is distributed under the terms of the Creative Commons Attribution License permitting unrestricted use and redistribution provided that the original author and source are credited.
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Maturing Mycobacterium smegmatis peptidoglycan requires non-canonical crosslinks to maintain shape
eLife 7:e37516.
https://doi.org/10.7554/eLife.37516
Further reading
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- Epidemiology and Global Health
- Microbiology and Infectious Disease
A better understanding of the mechanisms underpinning the growth of mycobacteria could help identify targets for new antibiotics.
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- Genetics and Genomics
- Microbiology and Infectious Disease
The sustained success of Mycobacterium tuberculosis as a pathogen arises from its ability to persist within macrophages for extended periods and its limited responsiveness to antibiotics. Furthermore, the high incidence of resistance to the few available antituberculosis drugs is a significant concern, especially since the driving forces of the emergence of drug resistance are not clear. Drug-resistant strains of Mycobacterium tuberculosis can emerge through de novo mutations, however, mycobacterial mutation rates are low. To unravel the effects of antibiotic pressure on genome stability, we determined the genetic variability, phenotypic tolerance, DNA repair system activation, and dNTP pool upon treatment with current antibiotics using Mycobacterium smegmatis. Whole-genome sequencing revealed no significant increase in mutation rates after prolonged exposure to first-line antibiotics. However, the phenotypic fluctuation assay indicated rapid adaptation to antibiotics mediated by non-genetic factors. The upregulation of DNA repair genes, measured using qPCR, suggests that genomic integrity may be maintained through the activation of specific DNA repair pathways. Our results, indicating that antibiotic exposure does not result in de novo adaptive mutagenesis under laboratory conditions, do not lend support to the model suggesting antibiotic resistance development through drug pressure-induced microevolution.
