Investigation of the Bacteriophage Community in Induced Lysates of Undefined Mesophilic Mixed-Strain DL-Cultures Using Classical and Metagenomic Approaches

To investigate the notion that starter cultures can be a reservoir of bacteriophages (phages) in the dairy environment, strains of three DL-starters (undefined mesophilic mixed-strain starters containing Lactococcus lactis subsp. lactis biovar. diacetylactis and Leuconostoc species) were selected and induced by mitomycin C, and the whole starters were induced spontaneously as well as by mitomycin C. Frequency of induction of 17%, 26% and 12% was estimated among the isolates of the three starters, with majority of the induced phages mostly showing morphological similarity to known P335 phages, and with a fraction of them showing atypical features. Sequences of P335 quasi-species phages were found to be the most frequent entities in almost all metaviromes derived from the induced lysates. However, sequences of Sk1virus phages (previously 936 phages) were emerged as the predominant entities following spontaneous induction of one of the starters, suggesting a phage-carrier state. Sequences of other phages such as 949, 1706, C2virus (previously c2 phages) and Leuconostoc species could also be observed but with a lower relative frequency. Taken together, the majority of the P335 quasi-species phages could represent the induced viral community of the starters, while the remaining phage groups mainly represent the background ambient viral community.

为探究发酵剂培养物（starter cultures）可作为乳制品环境中噬菌体（bacteriophages，简称phages）储存库这一假说，本研究选取3种DL发酵剂（DL-starters）的菌株，该类发酵剂为包含乳酸乳球菌乳酸亚种丁二酮乳生物型与明串珠菌属物种的未定义嗜温混合菌株发酵剂，采用丝裂霉素C进行诱导；同时对完整发酵剂分别开展自发诱导与丝裂霉素C诱导。经统计，3种发酵剂的分离菌株中诱导成功率分别为17%、26%与12%；多数诱导获得的噬菌体在形态上与已知P335噬菌体相似，另有部分噬菌体呈现非典型特征。在诱导裂解液的宏病毒组（metaviromes）中，P335准种噬菌体的序列几乎是最主要的病毒实体。但在其中一种发酵剂的自发诱导样本中，Sk1病毒属噬菌体（原936噬菌体）的序列成为优势物种，这提示存在噬菌体携带状态（phage-carrier state）。其他噬菌体类群如949、1706、C2病毒属噬菌体（原c2噬菌体）以及明串珠菌属相关序列也可被检测到，但相对丰度较低。综上，多数P335准种噬菌体可代表发酵剂的诱导病毒群落，而其余噬菌体类群则主要代表背景环境中的外源病毒群落。