The Integrative Conjugative Element (ICE) of Mycoplasma agalactiae : Key Elements Involved in Horizontal Dissemination and Influence of Coresident ICEs

Abstract

The discovery of integrative conjugative elements (ICEs) in wall-less mycoplasmas and the demonstration of their role in massive gene flows within and across species have shed new light on the evolution of these minimal bacteria. Of these, the ICE of the ruminant pathogen Mycoplasma agalactiae (ICEA) represents a prototype and belongs to a new clade of the Mutator-like superfamily that has no preferential insertion site and often occurs as multiple chromosomal copies. Here, functional genomics and mating experiments were combined to address ICEA functions and define the minimal ICEA chassis conferring conjugative properties to M. agalactiae. Data further indicated a complex interaction among coresident ICEAs, since the minimal ICEA structure was influenced by the occurrence of additional ICEA copies that can trans-complement conjugation-deficient ICEAs. However, this cooperative behavior was limited to the CDS14 surface lipoprotein, which is constitutively expressed by coresident ICEAs, and did not extend to other ICEA proteins, including the cis-acting DDE recombinase and components of the mating channel whose expression was detected only sporadically. Remarkably, conjugation-deficient mutants containing a single ICEA copy knocked out in cds14 can be complemented by neighboring cells expressing CDS14. This result, together with those revealing the conservation of CDS14 functions in closely related species, may suggest a way for mycoplasma ICEs to extend their interaction outside their chromosomal environment. Overall, this report provides a first model of conjugative transfer in mycoplasmas and offers valuable insights into understanding horizontal gene transfer in this highly adaptive and diverse group of minimal bacteria.

Genomic Islands in Mycoplasmas

“…This finding was supported by several direct and indirect evidences, including the monitoring of the integration of a mini-artificial ICE construct in M. agalactiae, genome sequencing of MICE flanking sequences and comparative genomics of MICEs in different species [30,31]. As identified by transposon mutagenesis or BLAST searches, a large portion of MICE genes are involved in the horizontal self-dissemination of the element [46]. MICEs also carry several hypothetical genes with no predicted function or no homology, with some being specific to a single mycoplasma species.…”

An emerging role for cyclic dinucleotide phosphodiesterase and nanoRNase activities in Mycoplasma bovis: Securing survival in cell culture

“…A notable exception is a group of proteins encoded by mobile elements in mycoplasmas that share similarities with type IV secretion systems [12][13][14][15]. These elements are responsible for massive exchanges of chromosomal material within and across mycoplasma species and contribute to the horizontal dissemination of new phenotypic traits [13,[15][16][17]. The paucity of secretion systems in mycoplasmas is consistent with the limited number of toxins so far identified in pathogenic species.…”

“…DNA constructions and oligonucleotide primers used in the present study are listed in S2 Table. Plasmid pOH/P was used as a backbone for complementation studies [16]. This plasmid was derived from p20-1miniO/T by replacing (i) the tetM region by the pac gene encoding a puromycin N-acetyltransferase [12], and (ii) the replication origin of M. agalactiae by its counterpart in HB0801 [33,51].…”

Mbov_0503 Encodes a Novel Cytoadhesin that Facilitates Mycoplasma bovis Interaction with Tight Junctions

“…Plasmid pMT85, which contains a modified version of transposon Tn4001 (mTn), was originally developed by Zimmerman and Herrmann [26]. Plasmid pOH/P was derived from p20-1miniO/T [27] by replacing (i) the tetM region by the pac gene, encoding a puromycin N-acetyltransferase [28], and (ii) the origin of replication of Mycoplasma agalactiae by its counterparts in M. bovis strain HB0801 [6]. For the complementation of M. bovis mutant T4.4, a DNA fragment containing the Mbov_0503 sequence under the control of M. agalactiae P40 promoter was synthesized (Beijing Tianyi Huiyuan Bioscience & Technology Inc.).…”

“…4. DNA constructions were verified by DNA sequencing and introduced in M. bovis by transformation, as previously described [27]. Plasmid pET-30a (Novagen, Darmstadt, Germany) was used for the expression of Mbov_0503 in Escherichia coli.…”