The Journal of antimicrobial chemotherapy · 2026
Intergeneric mobilization of a genomic island mediated by a helper integrative conjugative element from Streptococcus suis to Enterococcus faecalis.
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Nie Kaiwei, Zhao Jiaqi, Yin Cai, Gu Shushu, Ji Hui, Dai Xingyang, Wang Xiaoming, Wang Liping, Huang Jinhu
Аннотация
BACKGROUND AND OBJECTIVES: Mobile genetic elements drive antimicrobial-resistance dissemination in Gram-positive pathogens. In Streptococcus suis we previously identified a genomic island, GISsuJHJ17_rpsI, integrated at the conserved rpsI locus and carrying erm(B) and aadE. Here we investigated the genetic features and helper functions associated with mobilization of this island, including its transfer from S. suis to E. faecalis.
METHODS: Genetic annotation established that GISsuJHJ17_rpsI lacks a self-encoded conjugation apparatus but harbours an origin of transfer (oriT) sharing ∼85% nucleotide identity with the co-resident integrative and conjugative element (ICE). We performed filter-mating assays to test ICE-mediated mobilization in trans, constructed precise deletions of oriTGISsuJHJ17 and of the ICE relaxase, carried out complementation, and assessed fitness by growth and head-to-head competition of transconjugants.
RESULTS: Filter-mating assays showed that mobilization of GISsuJHJ17_rpsI in the S. suis recipient model required the helper-ICE relaxase and the candidate GI oriT region. Deletion of either determinant yielded no verified transconjugants under the assay conditions, whereas relaxase complementation and chromosomal oriT repair restored detectable transfer. These findings support a model in which the helper ICE provides the DNA-processing function required for GI mobilization, using the co-resident ICE transfer apparatus, as inferred from the ICE gene content. Fitness assays revealed no measurable growth defect or competitive disadvantage associated with acquisition of GISsuJHJ17_rpsI, indicating a minimal short-term fitness cost.
CONCLUSIONS: These findings show that GISsuJHJ17_rpsI can transfer from S. suis to E. faecalis and integrate at an rpsI-associated site. In the S. suis recipient model, mobilization required the helper-ICE relaxase and the GISsuJHJ17_rpsI oriT region, supporting a helper-ICE-dependent mechanism for genomic-island mobilization.
METHODS: Genetic annotation established that GISsuJHJ17_rpsI lacks a self-encoded conjugation apparatus but harbours an origin of transfer (oriT) sharing ∼85% nucleotide identity with the co-resident integrative and conjugative element (ICE). We performed filter-mating assays to test ICE-mediated mobilization in trans, constructed precise deletions of oriTGISsuJHJ17 and of the ICE relaxase, carried out complementation, and assessed fitness by growth and head-to-head competition of transconjugants.
RESULTS: Filter-mating assays showed that mobilization of GISsuJHJ17_rpsI in the S. suis recipient model required the helper-ICE relaxase and the candidate GI oriT region. Deletion of either determinant yielded no verified transconjugants under the assay conditions, whereas relaxase complementation and chromosomal oriT repair restored detectable transfer. These findings support a model in which the helper ICE provides the DNA-processing function required for GI mobilization, using the co-resident ICE transfer apparatus, as inferred from the ICE gene content. Fitness assays revealed no measurable growth defect or competitive disadvantage associated with acquisition of GISsuJHJ17_rpsI, indicating a minimal short-term fitness cost.
CONCLUSIONS: These findings show that GISsuJHJ17_rpsI can transfer from S. suis to E. faecalis and integrate at an rpsI-associated site. In the S. suis recipient model, mobilization required the helper-ICE relaxase and the GISsuJHJ17_rpsI oriT region, supporting a helper-ICE-dependent mechanism for genomic-island mobilization.