Liu Xiaodong, Luo Yantao, Li Zhefei, Wei Gehong
State Key Laboratory of Crop Stress Biology in Arid Areas, Shaanxi Key Laboratory of Agricultural and Environmental Microbiology, College of Life Sciences, Northwest Agriculture & Forestry University, Yangling, China.
Front Microbiol. 2018 Feb 20;9:263. doi: 10.3389/fmicb.2018.00263. eCollection 2018.
CCNWXJ12-2, isolated from root nodules of the desert plant , contains two type III secretion systems (T3SSs). T3SSs are specialized machinery with wide distribution in bacteria that inject effector proteins into target cells. Our previous study showed that the expression of T3SS1 is upregulated in high-salt conditions. Here, phylogenetic analysis of T3SS1 using the core protein RhcU suggested that T3SS1 belongs to the α-Rhc II subgroup of the Rhc T3SS family. To elaborate the function of CCNWXJ12-2 T3SS1 in stress adaption, two T3SS1 mutants ( and ) were constructed and analyzed. β-galactosidase transcriptional fusion assays showed that activity of the promoter of T3SS1 was induced by salts. Mutant was more sensitive to NaCl and LiCl than the wild-type, but was not. Both mutants were more sensitive to KCl than the wild-type. The intracellular Na concentration in in high-NaCl conditions (0.4 M) increased by 37% compared to that of the wild-type strain, while the Na concentration in increased by 13%. The K concentration in both mutants increased by 16% compared to the wild-type in high-KCl conditions (0.3 M). Strain showed decreased survival compared to the wild-type after treatment with HO, while the survival rate of was almost the same as that of the wild-type. Antioxidant enzyme activities in were lower than those in the wild-type strain, but this was not the case for . Our data elucidate the beneficial effects of T3SS1 in the adaption of CCNWXJ12-2 to stress.
从沙漠植物根瘤中分离得到的CCNWXJ12-2含有两个III型分泌系统（T3SSs）。T3SSs是在细菌中广泛分布的特殊机制，可将效应蛋白注入靶细胞。我们之前的研究表明，T3SS1在高盐条件下表达上调。在此，利用核心蛋白RhcU对T3SS1进行系统发育分析表明，T3SS1属于Rhc T3SS家族的α-Rhc II亚组。为阐明CCNWXJ12-2 T3SS1在应激适应中的功能，构建并分析了两个T3SS1突变体（ 和 ）。β-半乳糖苷酶转录融合分析表明，T3SS1启动子的活性受盐诱导。突变体 对NaCl和LiCl比野生型更敏感，但 不是。两个突变体对KCl都比野生型更敏感。在高NaCl条件（0.4 M）下， 中的细胞内Na浓度比野生型菌株增加了37%，而 中的Na浓度增加了13%。在高KCl条件（0.3 M）下，两个突变体中的K浓度比野生型增加了16%。用HO处理后，菌株 的存活率比野生型降低，而 的存活率与野生型几乎相同。 中的抗氧化酶活性低于野生型菌株，但 并非如此。我们的数据阐明了T3SS1在CCNWXJ12-2适应应激中的有益作用。
