Table_6_Comparative Genomics of Streptococcus thermophilus Support Important Traits Concerning the Evolution, Biology and Technological Properties of the Species.XLSX

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行业的重要起始菌种，具有极高的经济价值。本研究分析了乳酸链球菌热压变种的23个完全测序基因组，旨在凸显该物种进化、生物学特性及工艺特性的新视角。全基因组分析揭示，该物种拥有大量保守基因，且其全基因组可能即将封闭。根据全基因组系统发育和平均核苷酸同源性（ANI）分析，大多数乳酸链球菌热压变种菌株被分为两大主要簇（即簇A和簇B）。具体而言，簇A包括染色体长度超过1.83兆碱基对（Mbp）的菌株，而簇B包括染色体长度低于此阈值的菌株。这一观察结果提示，两个簇的菌株可能通过基因获得或丢失事件而有所区别。此外，簇A中某些菌株还可进一步细分为亚组，例如亚组I（ASCC 1275、DGCC 7710、KLDS SM、MN-BM-A02和ND07）、II（MN-BM-A01和MN-ZLW-002）、III（LMD-9和SMQ-301）以及IV（APC151和ND03）。簇B中某些菌株形成了一个独特的亚组，即亚组I（CNRZ1066、CS8、EPS和S9）。观察到的乳酸链球菌热压变种的簇和亚组表明，该物种内部存在世系，这一发现通过多个基因组性状的分布和/或结构得到不同程度的支持。这些性状包括胞外多糖（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）系统以及基因组岛（GIs）。值得注意的是，组氨酸生物合成簇存在于所有簇A菌株（包括NCTC12958T菌株）中，但在簇B的所有菌株中均不存在。其他与乳糖/半乳糖降解和尿素代谢、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起着核心作用。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，以进一步阐明该起始菌种内菌株多样性的重要方面，这些方面可能与它在乳制品行业中的应用相关。