A mycobacterial DivIVA domain-containing protein involved in cell length and septation

FhaA plays a key role in mycobacterial polar elongation and asymmetric growth

Mycobacteria, including pathogens like Mycobacterium tuberculosis, exhibit unique growth patterns and cell envelope structures that challenge our understanding of bacterial physiology. This study sheds light on FhaA, a conserved protein in Mycobacteriales, revealing its pivotal role in coordinating cell envelope biogenesis and asymmetric growth. The elucidation of the FhaA interactome in living mycobacterial cells reveals its participation in the protein network orchestrating cell envelope biogenesis and cell elongation/division. By manipulating FhaA levels, we uncovered its influence on cell morphology, cell envelope organization, and the localization of peptidoglycan biosynthesis machinery. Notably, fhaA deletion disrupted the characteristic asymmetric growth of mycobacteria, highlighting its importance in maintaining this distinctive feature. Our findings position FhaA as a key regulator in a complex protein network, orchestrating the asymmetric distribution and activity of cell envelope biosynthetic machinery. This work not only advances our understanding of mycobacterial growth mechanisms but also identifies FhaA as a potential target for future studies on cell envelope biogenesis and bacterial growth regulation. These insights into the fundamental biology of mycobacteria may pave the way for novel approaches to combat mycobacterial infections addressing the ongoing challenge of diseases like tuberculosis in global health.

IMPORTANCE

Mycobacterium tuberculosis, the bacterium responsible for tuberculosis, remains a global health concern. Unlike most well-studied model bacilli, mycobacteria possess a distinctive and complex cell envelope, as well as an asymmetric polar growth mode. However, the proteins and mechanisms that drive cell asymmetric elongation in these bacteria are still not well understood. This study sheds light on the role of the protein FhaA in this process. Our findings demonstrate that FhaA localizes at the septum and asymmetrically to the poles, with a preference for the fast-growing pole. Furthermore, we showed that FhaA is essential for population heterogeneity and asymmetric polar elongation and plays a role in the precise subcellular localization of the cell wall biosynthesis machinery. Mycobacterial asymmetric elongation results in a physiologically heterogeneous bacterial population which is important for pathogenicity and response to antibiotics, stressing the relevance of identifying new factors involved in these still poorly characterized processes.

A dispensable SepIVA orthologue in Streptomyces venezuelae is associated with polar growth and not cell division

BACKGROUND

SepIVA has been reported to be an essential septation factor in Mycolicibacterium smegmatis and Mycobacterium tuberculosis. It is a coiled-coil protein with similarity to DivIVA, a protein necessary for polar growth in members of the phylum Actinomycetota. Orthologues of SepIVA are broadly distributed among actinomycetes, including in Streptomyces spp.

RESULTS

To clarify the role of SepIVA and its potential involvement in cell division in streptomycetes, we generated sepIVA deletion mutants in Streptomyces venezuelae and found that sepIVA is dispensable for growth, cell division and sporulation. Further, mNeonGreen-SepIVA fusion protein did not localize at division septa, and we found no evidence of involvement of SepIVA in cell division. Instead, mNeonGreen-SepIVA was accumulated at the tips of growing vegetative hyphae in ways reminiscent of the apical localization of polarisome components like DivIVA. Bacterial two-hybrid system analyses revealed an interaction between SepIVA and DivIVA. The results indicate that SepIVA is associated with polar growth. However, no phenotypic effects of sepIVA deletion could be detected, and no evidence was observed of redundancy with the other DivIVA-like coiled-coil proteins Scy and FilP that are also associated with apical growth in streptomycetes.

CONCLUSIONS

We conclude that S. venezuelae SepIVA, in contrast to the situation in mycobacteria, is dispensable for growth and viability. The results suggest that it is associated with polar growth rather than septum formation.

Arginine methylation sites on SepIVA help balance elongation and septation in Mycobacterium smegmatis

The growth of mycobacterial cells requires successful coordination between elongation and septation. However, it is not clear which factors mediate this coordination. Here, we studied the function and post-translational modification of an essential division factor, SepIVA, in Mycobacterium smegmatis. We find that SepIVA is arginine methylated, and that alteration of its methylation sites affects both septation and polar elongation of Msmeg. Furthermore, we show that SepIVA regulates the localization of MurG and that this regulation may impact polar elongation. Finally, we map SepIVA's two regulatory functions to different ends of the protein: the N-terminus regulates elongation while the C-terminus regulates division. These results establish SepIVA as a regulator of both elongation and division and characterize a physiological role for protein arginine methylation sites for the first time in mycobacteria.

Corroboration of cross-reactivity between Mycobacterium leprae and hosts' salivary and cutaneous proteins: A hope for prognostic biomarkers for the pathogenesis of reactions in leprosy

Introduction

Immunological reactions are frequent complications that may occur either before, during, or after treatment and affect 30-50% of leprosy patients. The presence of autoantibodies like rheumatoid factor, antinuclear factor, and antibodies to host collagen, keratin, actin, myosin, endothelial cells, and myelin basic protein (MBP) has been earlier reported in leprosy patients. The purpose of this study was to identify cross-reactive proteins in clinical samples such as saliva and slit skin scrapings (SSS) of leprosy patients which could be utilised as prognostic biomarkers for Type 1 Reaction (T1R) in leprosy.

Method

A total of 10 leprosy patients in T1R and 5 healthy volunteers were recruited. The protein was extracted from their SSS and saliva samples, thereafter, isoelectric focusing (IEF) and two-dimensional PAGE were performed to analyse the proteins. Furthermore, the cross-reactivity was identified by western blotting host proteins in gel against purified IgG from Mycobacterium leprae soluble antigen (MLSA)- hyperimmunized rabbit sera, thereafter, cross-reactive proteins were identified by MS/MS. The cross-reactive host proteins were analysed for homologous bacterial proteins and B cell epitopes (BCEs) were predicted by using bioinformatic tools.

Results

A total of five spots of salivary proteins namely S100-A9, 35.3 kDa, and 41.5 kDa proteins, Serpin peptidase inhibitor (clade A), Cystatin SA-III, and four spots of SSS namely 41.4 kDa protein, Alpha-1 antitrypsin, vimentin, and keratin 1, were identified as cross-reactive. Further, a total of 22 BCEs of cross-reactive host proteins were predicted and visualised.

Discussion

This data provides strong evidence of cross-reactivity/molecular mimicry between host and pathogen in leprosy patients with reaction. These BCEs of cross-reactive proteins could be further studied to predict reactions and may be utilised as an early diagnostic biomarker for T1R in leprosy.