Supplementary Material for: Characterization of Two Temperate Lactobacillus paracasei Bacteriophages: Morphology, Kinetics and Adsorption

<b><i>Background/Aims:</i></b> Adsorption and kinetic parameters, latent period, burst size and burst time, are characteristics of phage/host systems and can be affected by several environmental factors. As only few studies have focused on temperate dairy phages, we characterized these parameters on temperate <i>Lactobacillus paracasei</i> phages Φ i<i>Lp</i>84 and Φ i<i>Lp</i>1308, infective for probiotic strains. <b><i>Methods:</i></b> Phages were characterized by transmission electron microscopy and genomic DNA restriction. Adsorption under different environmental conditions, phage kinetics and efficiency of plating (EOP) were determined using the double-layer titration method. <b><i>Results:</i></b> Phages Φ i<i>Lp</i>84 and Φ i<i>Lp</i>1308 belong to the <i>Siphoviridae</i> family and have genome sizes of 38 and 34 kbp, respectively. Adsorption was affected by calcium concentration, pH, temperature and host viability, and reached a limit at very high multiplicity of infection. Latency, burst time and burst size were of 85 min, 131 min and 46 for Φ i<i>Lp</i>84, and 51 min, 92 min and 28 for Φ i<i>Lp</i>1308, respectively, at 37°C. A clear influence of temperature on phage kinetics was observed. Regarding EOP, Φ i<i>Lp</i>84 produced plaques on only 1 out of 8 strains tested. <b><i>Conclusion:</i></b> Noticeable differences in adsorption, kinetics and EOP were found for two morphologically identical temperate <i>L. paracasei</i> phages of similar origin.

**研究背景与目的：** 吸附与动力学参数、潜伏期、裂解量及裂解时间均为噬菌体-宿主系统的核心特征，且可受多种环境因素调控。目前针对乳品温和噬菌体的相关研究较为匮乏，本研究针对两株可侵染益生菌菌株的副干酪乳杆菌（*Lactobacillus paracasei*）温和噬菌体ΦiLp84与ΦiLp1308，对上述参数进行了系统表征。

**研究方法：** 采用透射电子显微镜与基因组DNA限制性酶切技术完成噬菌体鉴定。通过双层平板滴定法，测定不同环境条件下的噬菌体吸附率、噬菌体动力学特征及噬斑形成效率（efficiency of plating, EOP）。

**研究结果：** ΦiLp84与ΦiLp1308均隶属于长尾噬菌体科（Siphoviridae），基因组大小分别为38 kbp与34 kbp。噬菌体吸附过程受钙离子浓度、pH值、温度及宿主活性的显著影响，且在极高感染复数下吸附率趋近于饱和。在37℃培养条件下，ΦiLp84的潜伏期、裂解时间与裂解量分别为85 min、131 min与46；ΦiLp1308的对应参数则分别为51 min、92 min与28。本研究观测到温度对噬菌体动力学特征具有显著调控作用。就噬斑形成效率（EOP）而言，ΦiLp84仅能在8株受试菌株中的1株上形成噬斑。

**研究结论：** 本研究发现，两株来源相近、形态一致的副干酪乳杆菌温和噬菌体，其吸附特性、动力学参数及噬斑形成效率存在显著差异。