Table_8_Comparative Genomics of Streptococcus thermophilus Support Important Traits Concerning the Evolution, Biology and Technological Properties of the Species.docx

Streptococcus thermophilus is a major starter for the dairy industry with great economic importance. In this study we analyzed 23 fully sequenced genomes of S. thermophilus to highlight novel aspects of the evolution, biology and technological properties of this species. Pan/core genome analysis revealed that the species has an important number of conserved genes and that the pan genome is probably going to be closed soon. According to whole genome phylogeny and average nucleotide identity (ANI) analysis, most S. thermophilus strains were grouped in two major clusters (i.e., clusters A and B). More specifically, cluster A includes strains with chromosomes above 1.83 Mbp, while cluster B includes chromosomes below this threshold. This observation suggests that strains belonging to the two clusters may be differentiated by gene gain or gene loss events. Furthermore, certain strains of cluster A could be further subdivided in subgroups, i.e., subgroup I (ASCC 1275, DGCC 7710, KLDS SM, MN-BM-A02, and ND07), II (MN-BM-A01 and MN-ZLW-002), III (LMD-9 and SMQ-301), and IV (APC151 and ND03). In cluster B certain strains formed one distinct subgroup, i.e., subgroup I (CNRZ1066, CS8, EPS, and S9). Clusters and subgroups observed for S. thermophilus indicate the existence of lineages within the species, an observation which was further supported to a variable degree by the distribution and/or the architecture of several genomic traits. These would include exopolysaccharide (EPS) gene clusters, Clustered Regularly Interspaced Short Palindromic Repeats (CRISPRs)-CRISPR associated (Cas) systems, as well as restriction-modification (R-M) systems and genomic islands (GIs). Of note, the histidine biosynthetic cluster was found present in all cluster A strains (plus strain NCTC12958T) but was absent from all strains in cluster B. Other loci related to lactose/galactose catabolism and urea metabolism, aminopeptidases, the majority of amino acid and peptide transporters, as well as amino acid biosynthetic pathways were found to be conserved in all strains suggesting their central role for the species. Our study highlights the necessity of sequencing and analyzing more S. thermophilus complete genomes to further elucidate important aspects of strain diversity within this starter culture that may be related to its application in the dairy industry.

乳酸链球菌热压变种是乳制品工业的主要启动菌，具有重要的经济价值。本研究分析了乳酸链球菌热压变种的23个全序列基因组，旨在突出该物种在进化、生物学和工艺特性方面的新颖方面。全基因组分析揭示了该物种拥有大量保守基因，并且全基因组可能即将闭合。根据全基因组系统发育和平均核苷酸一致性（ANI）分析，大多数乳酸链球菌热压变种菌株被分为两大类群（即类群A和类群B）。具体而言，类群A包括染色体大于1.83 Mbp的菌株，而类群B包括染色体小于此阈值的菌株。这一观察结果表明，属于两个类群的菌株可能通过基因获得或基因丢失事件而分化。此外，类群A中的某些菌株还可以进一步细分为亚群，例如亚群I（ASCC 1275、DGCC 7710、KLDS SM、MN-BM-A02和ND07）、亚群II（MN-BM-A01和MN-ZLW-002）、亚群III（LMD-9和SMQ-301）以及亚群IV（APC151和ND03）。在类群B中，某些菌株形成了一个独特的亚群，即亚群I（CNRZ1066、CS8、EPS和S9）。观察到的乳酸链球菌热压变种的类群和亚群表明，物种内部存在谱系，这一观察结果通过多种基因组特征的分布和/或结构在某种程度上得到了进一步的支持。这些特征包括外多糖（EPS）基因簇、成簇规律间隔短回文重复序列（CRISPRs）-CRISPR相关（Cas）系统、限制修饰（R-M）系统和基因组岛（GIs）。值得注意的是，组氨酸生物合成簇存在于所有类群A菌株（包括NCTC12958T菌株）中，但在所有类群B菌株中均不存在。其他与乳糖/半乳糖分解代谢、尿素代谢、氨肽酶、大多数氨基酸和肽转运蛋白以及氨基酸生物合成途径相关的位点在所有菌株中均被发现是保守的，这表明它们在物种中的核心作用。本研究强调了测序和分析更多乳酸链球菌热压变种完整基因组的重要性，以进一步阐明该启动菌中菌株多样性的重要方面，这些方面可能与其在乳制品工业中的应用有关。