Endolysins are produced by (bacterio)phages and play a crucial role in degrading the bacterial cell wall and the subsequent release of new phage progeny. These lytic enzymes exhibit a remarkable diversity, often occurring in a multimodular form that combines different catalytic and cell wall-binding domains, even in phages infecting the same species. Yet, our current understanding lacks insight into how environmental factors and ecological niches may have influenced the evolution of these enzymes. In this study, we focused on phages infecting Streptococcus. thermophilus, as this bacterial species has a well-defined and narrow ecological niche, namely, dairy fermentation. Among the endolysins found in phages targeting this species, we observed limited diversity, with a singular structural type dominating in most of identified S. thermophilus phages. Within this prevailing endolysin type, we discovered a novel and highly conserved calcium-binding motif. This motif proved to be crucial for the stability and activity of the enzyme at elevated temperatures. Ultimately, we demonstrated its positive selection within the host's environmental conditions, particularly under the temperature profiles encountered in the production of yogurt, mozzarella and hard cheeses that rely on S. thermophilus.

中文翻译：

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发酵实践选择噬菌体中的热稳定性内溶素

内溶素由（细菌）噬菌体产生，在降解细菌细胞壁和随后释放新噬菌体后代方面发挥着至关重要的作用。这些裂解酶表现出显着的多样性，通常以结合不同催化和细胞壁结合域的多模块形式出现，甚至在感染同一物种的噬菌体中也是如此。然而，我们目前的理解缺乏对环境因素和生态位如何影响这些酶的进化的深入了解。在这项研究中，我们重点关注感染链球菌的噬菌体。嗜热菌，因为这种细菌物种具有明确且狭窄的生态位，即乳制品发酵。在针对该物种的噬菌体中发现的内溶素中，我们观察到有限的多样性，在大多数已识别的嗜热链球菌噬菌体中，单一结构类型占主导地位。在这种流行的细胞内溶素类型中，我们发现了一种新颖且高度保守的钙结合基序。事实证明，该基序对于酶在高温下的稳定性和活性至关重要。最终，我们证明了它在宿主环境条件下的正选择，特别是在依赖嗜热链球菌生产酸奶、马苏里拉奶酪和硬奶酪时遇到的温度曲线下。