A mycobacterial DivIVA domain-containing protein involved in cell length and septation
Hayleah Pickford1, Emily Alcock2, Albel Singh1
1School of Biosciences and Institute of Microbiology and Infection, University of Birmingham, UK.
Abstract:
Mycobacterial cells elongate via polar deposition of cell wall material, similar to the filamentous Streptomyces species, which contain a tip-organizing centre. Coiled-coiled proteins such as DivIVA play an important role in this process. The genome of Mycobacterium tuberculosis, the causative agent of tuberculosis, encodes many coiled-coil proteins that are homologous to DivIVA with a potential role in mycobacterial cell elongation. Here we describe studies on Mycobacterium smegmatis MSMEG_2416, a homologue of M. tuberculosis Rv2927c. Two previous independent studies showed that MSMEG_2416 was involved in septation (subsequently referred to as sepIVA). Contrary to these previous reports, we found sepIVA to be dispensable for growth in laboratory media by generating a viable null mutant. The mutant strain did, however, show a number of differences, including a change in colony morphology and biofilm formation that could be reversed on complementation with sepIVA as well as Rv2927c, the sepIVA homologue from M. tuberculosis. However, analysis of cell wall lipids did not reveal any alterations in lipid profiles of the mutant strain. Microscopic examination of the mutant revealed longer cells with more septa, which occurred at irregular intervals, often generating mini-compartments, a profile similar to that observed in the previous studies following conditional depletion, highlighting a role for sepIVA in mycobacterial growth.
Insights
SepIVA, a coiled-coil protein in Mycobacterium smegmatis, is dispensable for growth but affects cell morphology and biofilm formation. Its homologue from Mycobacterium tuberculosis can complement these changes, suggesting a conserved role in mycobacterial growth.
Area of Science:
- Microbiology
- Cell Biology
Background:
- Mycobacterial cell elongation involves polar cell wall deposition, similar to Streptomyces, with DivIVA family coiled-coil proteins playing a key role.
- Mycobacterium tuberculosis encodes several DivIVA homologues, suggesting a potential role in cell elongation.
Purpose of the Study:
- To investigate the function of MSMEG_2416 (designated sepIVA), a DivIVA homologue in Mycobacterium smegmatis.
- To clarify the role of sepIVA in mycobacterial growth and cell division.
Main Methods:
- Generation and characterization of a viable sepIVA null mutant in Mycobacterium smegmatis.
- Complementation studies using sepIVA and its M. tuberculosis homologue Rv2927c.
- Microscopic examination of cell morphology and septation.
- Analysis of cell wall lipid profiles.
- Assessment of colony morphology and biofilm formation.
Main Results:
- The sepIVA null mutant is viable and grows in laboratory media, contrary to previous reports suggesting involvement in septation.
- Mutant strains exhibit altered colony morphology and biofilm formation, which are reversible upon complementation.
- Microscopic analysis reveals longer cells with increased, irregularly spaced septa in the mutant.
- No significant alterations in cell wall lipid profiles were observed in the mutant.
Conclusions:
- SepIVA is dispensable for Mycobacterium smegmatis growth but plays a significant role in regulating cell shape, septation, and biofilm formation.
- Rv2927c, the M. tuberculosis homologue, can functionally complement the sepIVA mutant, indicating a conserved role for these proteins in mycobacterial growth regulation.
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