Bassi D, Cappa F, Gazzola S, Orrù L, Cocconcelli P S
Istituto di Microbiologia, Centro Ricerche Biotecnologiche, Università Cattolica del Sacro Cuore, Piacenza and Cremona, Italy.
Consiglio per la Ricerca e la Sperimentazione in Agricoltura e l'Analisi dell'Economia Agraria, Centro di Ricerca per la Genomica Vegetale (CREA-GPG), Fiorenzuola d'Arda, Italy.
Appl Environ Microbiol. 2017 Mar 31;83(8). doi: 10.1128/AEM.02840-16. Print 2017 Apr 15.
In , gene transfer events and loss of ancestral traits over the years contribute to its high level of adaptation to milk environments. Biofilm formation capacity, a phenotype that is lost in the majority of strains, plays a role in persistence in dairy environments, such as milk pasteurization and cheese manufacturing plants. To investigate this property, we have studied UC8547, a fast-acidifying dairy starter culture selected for its high capacity to form biofilm on stainless steel under environmental conditions resembling the dairy environment. Using a dynamic flow cell apparatus, it was shown that UC8547 biofilm formation on stainless steel depends on the presence of milk proteins. From this strain, which harbors the gene for the cell wall protease and shows an aggregative phenotype, spontaneous mutants with impaired biofilm capacity can be isolated at high frequency. These mutants lack the PrtS expendable island, as confirmed by comparison of the genome sequence of UC8547Δ3 with that of the parent strain. The island excision occurs between two 26-bp direct repeats located in the two copies of the IS flanking this genomic island. The central role of PrtS was confirmed by analyzing the derivative strain UC8547Δ16, whose gene was interrupted by an insertional mutation, thereby making it incapable of biofilm formation. PrtS, acting as a binding substance between the milk proteins adhered to stainless steel and cell envelopes, mediates biofilm formation in dairy environments. This feature provides with an ecological benefit for its survival and persistence in this environment. The increased persistence of biofilm has consequences in the dairy environment: if, on the one hand, the release of this microorganism from biofilm can promote the fermentation of artisanal cheeses, under industrial conditions it may lead to undesirable contamination of dairy products. The study of the molecular mechanism driving biofilm formation provides increased knowledge on how an ancestral trait affects relevant phenotypes, such as persistence in the environment and efficiency of growth in milk. This study provides insight into the genetic factors affecting biofilm formation at dairy plants.
多年来，基因转移事件和祖先性状的丧失促成了其对牛奶环境的高度适应性。生物膜形成能力是大多数菌株中丧失的一种表型，在乳制品环境（如牛奶巴氏杀菌厂和奶酪制造厂）的持久性方面发挥着作用。为了研究这一特性，我们研究了UC8547，这是一种快速酸化的乳制品发酵剂培养物，因其在类似于乳制品环境的条件下在不锈钢上形成生物膜的高能力而被选择。使用动态流动池装置表明，UC8547在不锈钢上的生物膜形成取决于牛奶蛋白的存在。从这个携带细胞壁蛋白酶基因并表现出聚集表型的菌株中，可以高频分离出生物膜能力受损的自发突变体。通过比较UC8547Δ3与亲本菌株的基因组序列证实，这些突变体缺乏PrtS可消耗岛。该岛切除发生在位于该基因组岛两侧的IS的两个拷贝中的两个26bp直接重复序列之间。通过分析衍生菌株UC8547Δ16证实了PrtS的核心作用，其基因被插入突变中断，从而使其无法形成生物膜。PrtS作为粘附在不锈钢上的牛奶蛋白与细胞包膜之间的结合物质，介导乳制品环境中的生物膜形成。这一特性为其在该环境中的生存和持久性提供了生态益处。生物膜的持久性增加在乳制品环境中会产生后果：一方面，如果这种微生物从生物膜中释放可以促进手工奶酪的发酵，在工业条件下它可能会导致乳制品的不良污染。对驱动生物膜形成的分子机制的研究增加了对祖先性状如何影响相关表型（如在环境中的持久性和在牛奶中的生长效率）的认识。这项研究深入了解了影响乳制品厂生物膜形成的遗传因素。
