Mobilization of horizontally acquired island 2 is induced in planta in the phytopathogen Pectobacterium atrosepticum SCRI1043 and involves the putative relaxase ECA0613 and quorum sensing

Abstract

Integrative and conjugative elements (ICEs) contribute to the rapid evolution of bacterial pathogens via horizontal gene transfer of virulence determinants. ICEs have common mechanisms for transmission, yet the cues triggering this process under natural environmental or physiological conditions are largely unknown. In this study, mobilization of the putative ICE horizontally acquired island 2 (HAI2), present in the chromosome of the phytopathogen Pectobacterium atrosepticum SCRI1043, was examined during infection of the host plant potato. Under these conditions, mobilization of HAI2 increased markedly compared with in vitro cultures. In planta-induced mobilization of HAI2 was regulated by quorum sensing and involved the putative ICE-encoded relaxase ECA0613. Disruption of ECA0613 also reduced transcription of genes involved in production of coronafacic acid (Cfa), the major virulence factor harboured on HAI2, whereas their expression was unaffected in the quorum-sensing (expI) mutant. Thus, suppression of cfa gene expression was not regulated by the mobilization of the ICE per se, but was due directly to inactivation of the relaxase. The identification of genetic factors associated solely with in planta mobilization of an ICE demonstrates that this process is highly adapted to the natural environment of the bacterial host and can influence the expression of virulence determinants.

Pectobacterium atrosepticum and Pectobacterium carotovorum Harbor Distinct, Independently Acquired Integrative and Conjugative Elements Encoding Coronafacic Acid that Enhance Virulence on Potato Stems

“…In these experiments, both attP and attB 0515 were detected in all isolates ( Figure 2 ). The ratios for attP and attB 0515 were 2.25 × 10 -5 and 8.45 × 10 -6 in P. atrosepticum SCRI1043, consistent with the low frequency of HAI2 excision from the phe -tRNA gene immediately downstream of ECA0515 and the formation of the circular extrachromosomal form reported previously ( Vanga et al, 2012 , 2015 ). The relative proportion of attP compared to attB 0515 calculated using these ratios was 2.67.…”

“…HAI2 is no exception, integrated within the genome of P. atrosepticum SCRI1043 at a bacterial attachment site ( attB 0515 ) located within the phe -tRNA gene immediately downstream of ECA0515 ( Vanga et al, 2012 ). HAI2 can excise at low frequency from the chromosome ( Vanga et al, 2012 ), a process that is induced in planta ( Vanga et al, 2015 ). Mobilization and transfer of ICEs plays a central role in the evolution of pathogens by transferring large amounts of genetic information between bacteria ( Morschhäuser et al, 2000 ).…”

Pathogenicity island excision during an infection by Salmonella enterica serovar Enteritidis is required for crossing the intestinal epithelial barrier in mice to cause systemic infection

“…Several members of Enterobacteriaceae family have on their chromosome a type of excisable PAIs denominated ROD21-like islands [26,27]. This is the case of Salmonella sp (ROD21 and SPI-7) [23], Escherichia coli UPEC (PAI I536, PAI II536, and PAI V536) [36], Klebsiella pneumoniae (GIE492) [37], Vibrio cholera (VPI-2 VSP-I and VSP-I) [38], and Pectobacterium atrosepticum (HAI2) [39]. These islands have significant structural conservation, displaying an unusual G + C profile, are inserted downstream a tRNA gene (usually Asp or Ser), have DRS at the 3´end of the PAI and typically encode paralogs of H-NS (hnsB) and/or an H-NS antagonist [26,40].…”

Regulation of conjugative transfer of plasmids and integrative conjugative elements

“…One of them, horizontally acquired island 2 (HAI2) has genes involved in pathogenesis (cfa-like polyketide phytotoxin clusters) (Bell et al, 2004). Excision and transfer of HAI2 is induced in planta by unknown compounds and is also modulated by QS (Vanga et al, 2015). In Pseudomonas aeruginosa, it was described that the selftransmissible pathogenicity island PAPI-1 carries over one hundred genes with several…”