TY - JOUR

T1 - Maintenance of the Shigella sonnei Virulence Plasmid Is Dependent on Its Repertoire and Amino Acid Sequence of Toxin-Antitoxin Systems

AU - Martyn, Jessica E.

AU - Pilla, Giulia

AU - Hollingshead, Sarah

AU - Winther, Kristoffer S.

AU - Lea, Susan

AU - McVicker, Gareth

AU - Tang, Christoph M.

N1 - Publisher Copyright: Copyright © 2022 Martyn et al.

PY - 2022

Y1 - 2022

N2 - Shigella sonnei is a major cause of bacillary dysentery and an increasing concern due to the spread of multidrug resistance. S. sonnei harbors pINV, an;210 kb plasmid that encodes a type III secretion system (T3SS), which is essential for virulence. During growth in the laboratory, avirulence arises spontaneously in S. sonnei at high frequency, hampering studies on and vaccine development against this important pathogen. Here, we investigated the molecular basis for the emergence of avirulence in S. sonnei and showed that avirulence mainly results from pINV loss, which is consistent with previous findings. Ancestral deletions have led to the loss from S. sonnei pINV of two toxin-antitoxin (TA) systems involved in plasmid maintenance, CcdAB and GmvAT, which are found on pINV in Shigella flexneri. We showed that the introduction of these TA systems into S. sonnei pINV reduced but did not eliminate pINV loss, while the single amino acid polymorphisms found in the S. sonnei VapBC TA system compared with S. flexneri VapBC also contributed to pINV loss. Avirulence also resulted from deletions of T3SS-associated genes in pINV through recombination between insertion sequences (ISs) on the plasmid. These events differed from those observed in S. flexneri due to the different distribution and repertoire of ISs. Our findings demonstrated that TA systems and ISs influenced plasmid dynamics and loss in S. sonnei and could be exploited for the design and evaluation of vaccines.

AB - Shigella sonnei is a major cause of bacillary dysentery and an increasing concern due to the spread of multidrug resistance. S. sonnei harbors pINV, an;210 kb plasmid that encodes a type III secretion system (T3SS), which is essential for virulence. During growth in the laboratory, avirulence arises spontaneously in S. sonnei at high frequency, hampering studies on and vaccine development against this important pathogen. Here, we investigated the molecular basis for the emergence of avirulence in S. sonnei and showed that avirulence mainly results from pINV loss, which is consistent with previous findings. Ancestral deletions have led to the loss from S. sonnei pINV of two toxin-antitoxin (TA) systems involved in plasmid maintenance, CcdAB and GmvAT, which are found on pINV in Shigella flexneri. We showed that the introduction of these TA systems into S. sonnei pINV reduced but did not eliminate pINV loss, while the single amino acid polymorphisms found in the S. sonnei VapBC TA system compared with S. flexneri VapBC also contributed to pINV loss. Avirulence also resulted from deletions of T3SS-associated genes in pINV through recombination between insertion sequences (ISs) on the plasmid. These events differed from those observed in S. flexneri due to the different distribution and repertoire of ISs. Our findings demonstrated that TA systems and ISs influenced plasmid dynamics and loss in S. sonnei and could be exploited for the design and evaluation of vaccines.

KW - Insertion sequences

KW - Shigella sonnei

KW - T3SS

KW - TA systems

KW - VapBC

KW - Virulence plasmid

U2 - 10.1128/jb.00519-21

DO - 10.1128/jb.00519-21

M3 - Journal article

C2 - 34978459

AN - SCOPUS:85126831054

VL - 204

JO - Journal of Bacteriology

JF - Journal of Bacteriology

SN - 0021-9193

IS - 3

M1 - e00519-21

ER -