Gao Lijuan, Tan Yahong, Zhang Weican, Qi Qingsheng, Lu Xuemei
State Key Laboratory of Microbial Technology, Shandong University, Qingdao, China.
Front Microbiol. 2021 Feb 12;12:628555. doi: 10.3389/fmicb.2021.628555. eCollection 2021.
The type IX secretion system (T9SS) is a novel protein secretion system, which is found in and confined to the phylum . T9SS is involved in the secretion of virulence factors, cell surface adhesins, and complex biopolymer degrading enzymes to the cell surface or extracellular medium. is a widely distributed bacterium, which is able to efficiently digest cellulose and rapidly glide along the solid surfaces. has a full set of orthologs of T9SS components. However, the functions of most homologous proteins have not been verified. In . , CHU_0029 and CHU_2709 are similar in sequence to T9SS components SprA and SprT, respectively. In this study, the single deletion mutants of () and () were obtained using a complex medium with the addition of Ca and Mg. Single deletion of or resulted in defects in cellulose utilization and gliding motility. Moreover, the Δ and Δ mutants showed growth defects in Ca- and Mg-deficient media. The results of ICP-MS test showed that both the whole cell and intracellular concentrations of Ca were dramatically reduced in the Δ and Δ mutants, indicating that SprA and SprT are both important for the assimilation of trace amount of Ca. While the assimilation of Mg was not obviously influenced in the Δ and Δ mutants. Through proteomics analysis of the cell surface proteins of the wild type and mutants, we found that the Δ and Δ mutants were defective in secretion of the majority of T9SS substrates. Together, these results indicate that SprA and SprT are both essential components of . T9SS, which is required for protein secretion, Ca acquisition, cellulose degradation, and gliding motility in Our study shed more light on the functions of SprA and SprT in T9SS, and further proved the link between the T9SS and Ca uptake system.
IX型分泌系统（T9SS）是一种新型蛋白质分泌系统，存在于特定门类中且局限于此。T9SS参与将毒力因子、细胞表面黏附素和复杂生物聚合物降解酶分泌到细胞表面或细胞外介质中。[细菌名称]是一种广泛分布的细菌，能够高效消化纤维素并沿固体表面快速滑行。[细菌名称]拥有T9SS组分的全套直系同源物。然而，大多数同源蛋白的功能尚未得到验证。在[细菌名称]中，CHU_0029和CHU_2709的序列分别与T9SS组分SprA和SprT相似。在本研究中，通过添加钙和镁的复合培养基获得了[细菌名称]中chu_0029（Δchu_0029）和chu_2709（Δchu_2709）的单缺失突变体。单独缺失chu_0029或chu_2709会导致纤维素利用和滑行运动缺陷。此外，Δchu_0029和Δchu_2709突变体在缺钙和缺镁培养基中表现出生长缺陷。电感耦合等离子体质谱（ICP-MS）测试结果表明，Δchu_0029和Δchu_2709突变体的全细胞和细胞内钙浓度均显著降低，表明SprA和SprT对微量钙的同化均很重要。而Δchu_0029和Δchu_2709突变体中镁的同化没有受到明显影响。通过对野生型和突变体细胞表面蛋白的蛋白质组学分析，我们发现Δchu_0029和Δchu_2709突变体在大多数T9SS底物的分泌方面存在缺陷。综上所述，这些结果表明SprA和SprT都是[细菌名称]T9SS的必需组分，该系统对于[细菌名称]中的蛋白质分泌、钙获取、纤维素降解和滑行运动是必需的。我们的研究进一步揭示了SprA和SprT在T9SS中的功能，并进一步证明了T9SS与钙摄取系统之间的联系。
