Giovanetti Eleonora, Brenciani Andrea, Morroni Gianluca, Tiberi Erika, Pasquaroli Sonia, Mingoia Marina, Varaldo Pietro E
Unit of Microbiology, Department of Life and Environmental Sciences, Polytechnic University of Marche Ancona, Italy.
Unit of Microbiology, Department of Biomedical Sciences and Public Health, Polytechnic University of Marche Medical School Ancona, Italy.
Front Microbiol. 2015 Jan 8;5:746. doi: 10.3389/fmicb.2014.00746. eCollection 2014.
Φm46.1 - Streptococcus pyogenes bacteriophage carrying mef(A) and tet(O), respectively, encoding resistance to macrolides (M phenotype) and tetracycline - is widespread in S. pyogenes but has not been reported outside this species. Φm46.1 is transferable in vitro among S. pyogenes isolates, but no information is available about its transferability to other Streptococcus species. We thus investigated Φm46.1 for its ability to be transduced in vitro to recipients of different Streptococcus species. Transductants were obtained from recipients of Streptococcus agalactiae, Streptococcus gordonii, and Streptococcus suis. Retransfer was always achieved, and from S. suis to S. pyogenes occurred at a much greater frequency than in the opposite direction. In transductants Φm46.1 retained its functional properties, such as inducibility with mitomycin C, presence both as a prophage and as a free circular form, and transferability. The transductants shared the same Φm46.1 chromosomal integration site as the donor, at the 3' end of a conserved RNA uracil methyltransferase (rum) gene, which is an integration hotspot for a variety of genetic elements. No transfer occurred to recipients of Streptococcus pneumoniae, Streptococcus oralis, and Streptococcus salivarius, even though rum-like genes were also detected in the sequenced genomes of these species. A largely overlapping 18-bp critical sequence, where the site-specific recombination process presumably takes place, was identified in the rum genes of all recipients, including those of the species yielding no transductants. Growth assays to evaluate the fitness cost of Φm46.1 acquisition disclosed a negligible impact on S. pyogenes, S. agalactiae, and S. gordonii transductants and a noticeable fitness advantage in S. suis. The S. suis transductant also displayed marked overexpression of the autolysin-encoding gene atl.
噬菌体Φm46.1分别携带mef(A)和tet(O)，编码对大环内酯类抗生素的抗性（M表型）和对四环素的抗性，它在化脓性链球菌中广泛存在，但在该物种之外尚未见报道。噬菌体Φm46.1在体外可在化脓性链球菌分离株之间转移，但尚无关于其向其他链球菌物种转移能力的信息。因此，我们研究了噬菌体Φm46.1在体外转导至不同链球菌物种受体的能力。从无乳链球菌、戈登氏链球菌和猪链球菌的受体中获得了转导子。转导子总是能够再次转移，并且从猪链球菌到化脓性链球菌的转移频率比相反方向高得多。在转导子中，噬菌体Φm46.1保留了其功能特性，如对丝裂霉素C的诱导性、作为前噬菌体和游离环状形式的存在以及可转移性。转导子与供体具有相同的噬菌体Φm46.1染色体整合位点，位于保守的RNA尿嘧啶甲基转移酶（rum）基因的3'端，该位点是多种遗传元件的整合热点。即使在肺炎链球菌、口腔链球菌和唾液链球菌的测序基因组中也检测到了rum样基因，但它们的受体均未发生转移。在所有受体的rum基因中，包括那些未产生转导子的物种，都鉴定出了一个大部分重叠的18bp关键序列，推测该序列是位点特异性重组过程发生的位置。评估获得噬菌体Φm46.1的适应性代价的生长试验表明，对化脓性链球菌、无乳链球菌和戈登氏链球菌转导子的影响可忽略不计，而在猪链球菌中则具有明显的适应性优势。猪链球菌转导子还显示出自溶素编码基因atl的显著过表达。
