Biology subjects

Mariano, G.

Publications and source records attributed to Mariano, G..

3 recordsLinked to original sources

bioRxiv2022

Homologous recombination between tandem paralogues drives evolution of Type VII secretion system immunity genes in firmicute bacteria

The Type VII secretion system (T7SS) is found in many Gram-positive firmicutes and secretes protein toxins that mediate bacterial antagonism. Two T7SS toxins have been identified in Staphylococcus aureus, EsaD a nuclease toxin that is counteracted by the EsaG immunity protein, and TspA, which has membrane depolarising activity and is neutralised by TsaI. Both toxins are polymorphic, and strings of non-identical esaG and tsaI immunity genes are encoded in all S. aureus strains. To investigate the evolution of esaG repertoires, we analysed the sequences of the tandem esaG genes and their encoded proteins. We identified three blocks of high sequence similarity shared by all esaG genes and identified evidence of extensive recombination events between esaG paralogues facilitated through these conserved sequence blocks. Recombination between these blocks accounts for loss and expansion of esaG genes in S. aureus genomes and we identified evidence of such events during evolution of strains in clonal complex 8. TipC, an immunity protein for the TelC lipid II phosphatase toxin secreted by the streptococcal T7SS, is also encoded by multiple gene paralogues. Two blocks of high sequence similarity locate to the 5 and 3 end of tipC genes, and we found strong evidence for recombination between tipC paralogues encoded by Streptococcus mitis BCC08. By contrast, we found only a single homology block across tsaI genes, and little evidence for intergenic recombination within this gene family. We conclude that homologous recombination is one of the drivers for the evolution of T7SS immunity gene clusters. DATA SUMMARYAll sequence data for strains used in this study are available on NCBI under BioProject PRJNA789916. Sequences from the NCTC3000 project are available on NCBI under BioProject PRJEB6403. Supplementary data 2 and all custom scripts are available on Github: https://github.com/GM110Z/Garret-et-al.-recombination-paper. IMPACT STATEMENTThe type VII secretion system (T7SS) in firmicutes secretes polymorphic toxins that target other bacteria. To protect from the action of these toxins, bacteria carry multiple paralogous copies of immunity protein-encoding genes that are sequence-related but non-identical. To date, little is known about how T7 immunity gene families evolve. In this study we analysed a cluster of EsaG-encoding genes in Staphylococcus aureus which are found at the ess/T7 secretion locus and provide immunity against the T7 secreted nuclease toxin, EsaD. We identified three homology blocks covering esaG genes and their downstream intergenic regions, which are separated by two variable regions. We have shown that recombination can occur between these homology blocks, leading to loss or expansion of esaG genes at this locus. Using a historical dataset of closely related S. aureus strains from clonal complex 8, we identified several independent recombination events leading to changes in the esaG repertoire. We further showed that similar events are observed for an immunity protein encoded by Group B Streptococcus spp. suggesting that recombination plays a broader role in the evolution of T7SS immunity-encoding genes. We speculate that gain and loss of T7 immunity genes is weighed in response to environmental pressure and metabolic burden.

microbiology↗

bioRxiv2021

Oligomerization of the FliF domains suggests a coordinated assembly of the bacterial flagellum MS ring

The bacterial flagellum is a complex, self-assembling macromolecular machine that powers bacterial motility. It plays diverse roles in bacterial virulence, including aiding in colonization and dissemination during infection. The flagellum consists of a filamentous structure protruding from the cell, and the basal body, a large assembly that spans the cell envelope. The basal body is comprised of over 10 different proteins, forming several concentric ring structures, termed the M- S- L- P- and C-rings, respectively. In particular, the MS rings are formed by a single protein FliF, which consists of two trans-membrane helices anchoring it to the inner membrane and surrounding a large periplasmic domain. Assembly of the MS ring, through oligomerization of FliF, is one of the first steps of basal body assembly. Previous computational analysis had shown that the periplasmic region of FliF consists of three structurally similar domains, termed Ring-Building Motif (RBM)1, RBM2 and RBM3. The structure of the MS-ring has been reported recently, and unexpectedly shown that these three domains adopt different symmetries, with RBM3 having a 34-mer stoichiometry, while RBM2 adopts two distinct positions in the complex, including a 23-mer ring. This observation raises some important question on the assembly of the MS ring, and the formation of this symmetry mis-match within a single protein. In this study, we analyze the oligomerization of the individual RBM domains in isolation, in the Salmonella typhimurium FliF orthologue. We demonstrate that the periplasmic domain of FliF assembles into the MS ring, in the absence of the trans-membrane helices. We also report that the RBM2 and RBM3 domains oligomerize into ring structures, but not RBM1. Intriguingly, we observe that a construct encompassing RBM1 and RBM2 is monomeric, suggesting that RBM1 interacts with RBM2, and inhibits its oligomerization. However, this inhibition is lifted by the addition of RBM3. Collectively, this data suggests a mechanism for the controlled assembly of the MS ring.

biophysics↗

bioRxiv2019

A new family of Type VI secretion system-delivered effector proteins displays ion-selective pore-forming activity

Type VI secretion systems (T6SSs) are nanomachines widely used by bacteria to compete with rivals. T6SSs deliver multiple toxic effector proteins directly into neighbouring cells and play key roles in shaping diverse polymicrobial communities. A number of families of T6SS-dependent anti-bacterial effectors have been characterised, however the mode of action of others remains unknown. Here we report that Ssp6, an anti-bacterial effector delivered by the Serratia marcescens T6SS, is an ion-selective pore-forming toxin. In vivo, Ssp6 inhibits growth by causing depolarisation of the inner membrane of intoxicated cells and also leads to increased outer membrane permeability, whilst reconstruction of Ssp6 activity in vitro demonstrated that it forms cation-selective pores. A survey of bacterial genomes revealed that Ssp6-like effectors are widespread in Enterobacteriaceae and often linked with T6SS genes. We conclude that Ssp6 represents a new family of T6SS-delivered anti-bacterial effectors, further diversifying the portfolio of weapons available for deployment during inter-bacterial conflict.

microbiology↗