Klotz Courtney, Goh Yong Jun, O'Flaherty Sarah, Johnson Brant, Barrangou Rodolphe
Genomic Sciences Graduate Program, North Carolina State University, Raleigh, NC, United States.
Department of Food, Bioprocessing and Nutrition Sciences, North Carolina State University, Raleigh, NC, United States.
Front Microbiol. 2020 Mar 17;11:345. doi: 10.3389/fmicb.2020.00345. eCollection 2020.
Bacterial surface-layers (S-layers) are crystalline arrays of repeating proteinaceous subunits that coat the exterior of many cell envelopes. S-layers have demonstrated diverse functions in growth and survival, maintenance of cell integrity, and mediation of host interactions. Additionally, S-layers can act as scaffolds for the outward display of auxiliary proteins and glycoproteins. These non-covalently bound S-layer associated proteins (SLAPs) have characterized roles in cell division, adherence to intestinal cells, and modulation of the host immune response. Recently, IgdA (LBA0695), a SLAP that possesses a Group 3 immunoglobulin (Ig)-like domain and GW (Gly-Tryp) dipeptide surface anchor, was recognized for its high conservation among S-layer-forming lactobacilli, constitutive expression, and surface localization. These findings prompted its selection for examination within the present study. Although IgdA and corresponding orthologs were shown to be unique to host-adapted lactobacilli, the Ig domain itself was specific to vertebrate-adapted species suggesting a role in vertebrate adaptation. Using a counterselective gene replacement system, was deleted from the NCFM chromosome. The resultant mutant, NCK2532, exhibited a visibly disrupted cell surface which likely contributed to its higher salt sensitivity, severely reduced adhesive capacity, and altered immunogenicity profile. Transcriptomic analyses revealed the induction of several stress response genes and secondary surface proteins. Due to the broad impact of IgdA on the cellular physiology and probiotic attributes of , identification of similar proteins in alternative bacterial species may help pinpoint next-generation host-adapted probiotic candidates.
细菌表面层（S层）是由重复的蛋白质亚基组成的晶体阵列，覆盖许多细胞包膜的外部。S层在生长和存活、维持细胞完整性以及介导宿主相互作用方面具有多种功能。此外，S层可作为辅助蛋白和糖蛋白向外展示的支架。这些非共价结合的S层相关蛋白（SLAPs）在细胞分裂、粘附于肠道细胞以及调节宿主免疫反应中具有特定作用。最近，IgdA（LBA0695），一种具有第3组免疫球蛋白（Ig）样结构域和GW（甘氨酸-色氨酸）二肽表面锚定的SLAP，因其在形成S层的乳酸杆菌中高度保守、组成型表达和表面定位而受到关注。这些发现促使其在本研究中被选择进行检测。尽管IgdA和相应的直系同源物被证明是宿主适应性乳酸杆菌所特有的，但Ig结构域本身是脊椎动物适应性物种所特有的，这表明其在脊椎动物适应性中发挥作用。使用反选择基因替换系统，从NCFM染色体中删除了 。产生的突变体NCK2532表现出明显破坏的细胞表面，这可能导致其更高的盐敏感性、严重降低的粘附能力和改变的免疫原性谱。转录组分析揭示了几种应激反应基因和次要表面蛋白的诱导。由于IgdA对 的细胞生理学和益生菌特性有广泛影响，在其他细菌物种中鉴定类似蛋白可能有助于确定下一代宿主适应性益生菌候选物。
