Shu Xia, Sun Xiting, Wang Kesu, Duan Yan, Liu Yunpeng, Zhang Ruifu
State Key Laboratory of Efficient Utilization of Arid and Semi-Arid Arable Land in Northern China, The Institute of Agricultural Resources and Regional Planning, Chinese Academy of Agricultural Sciences, Beijing 100081, China.
College of Life Science and Technology, Huazhong Agricultural University, Wuhan 430070, China.
Int J Mol Sci. 2025 Mar 13;26(6):2592. doi: 10.3390/ijms26062592.
Rhizosphere bacteria always compete intensely for ecological niches, employing various strategies to inhibit the growth of microbial competitors. One such strategy, contact-dependent inhibition (CDI), involves the direct delivery of toxic proteins into competing neighboring bacteria by a secretion system, leading to the inhibition of their growth. However, the ecological function of CDI competition in the natural environment remains unclear. In this study, we examined the role of the type VII secretion system (T7SS) substrate LXG domain-containing protein in the rhizobacterium SQR9 and found that SQR9 encodes LXG toxins mediate contact-dependent inhibition against other strains in biofilms. Transcriptional analysis revealed that the expression of these lxg genes is induced by root exudates and positively correlates with that of the T7SS gene cluster. We further confirmed that the survival of the mutants deficient of the LXG toxins was significantly decreased in natural soil. These findings highlight the critical role of T7SS and its substrate LXG toxins in competition of species in the rhizosphere, providing new insights into the ecological importance of CDI in natural environments.
根际细菌总是为争夺生态位而激烈竞争，它们采用各种策略来抑制微生物竞争者的生长。其中一种策略，即接触依赖性抑制（CDI），涉及通过分泌系统将有毒蛋白质直接传递到相邻的竞争细菌中，从而抑制它们的生长。然而，CDI竞争在自然环境中的生态功能仍不清楚。在本研究中，我们研究了根际细菌SQR9中含VII型分泌系统（T7SS）底物LXG结构域的蛋白质的作用，发现SQR9编码的LXG毒素介导生物膜中对其他菌株的接触依赖性抑制。转录分析表明，这些lxg基因的表达受根系分泌物诱导，并与T7SS基因簇的表达呈正相关。我们进一步证实，缺乏LXG毒素的突变体在天然土壤中的存活率显著降低。这些发现突出了T7SS及其底物LXG毒素在根际物种竞争中的关键作用，为CDI在自然环境中的生态重要性提供了新的见解。
